Various repair events following CRISPR/Cas9-based mutational correction of an infertility-related mutation in mouse embryos

PURPOSE

Unpredictable genetic modifications and chromosomal aberrations following CRISPR/Cas9 administration hamper the efficacy of germline editing. Repair events triggered by double-strand DNA breaks (DSBs) besides non-homologous end joining and repair template-driven homology-directed repair have been insufficiently investigated in mouse. In this work, we are the first to investigate the precise repair mechanisms triggered by parental-specific DSB induction in mouse for paternal mutational correction in the context of an infertility-related mutation.

METHODS

We aimed to correct a paternal 22-nucleotide deletion in Plcz1, associated with lack of fertilisation in vitro, by administrating CRISPR/Cas9 components during intracytoplasmic injection of Plcz1-null sperm in wild-type oocytes combined with assisted oocyte activation. Through targeted next-generation sequencing, 77 injected embryos and 26 blastomeres from seven injected embryos were investigated. In addition, low-pass whole genome sequencing was successfully performed on 17 injected embryo samples.

RESULTS

Repair mechanisms induced by two different CRISPR/Cas9 guide RNA (gRNA) designs were investigated. In 13.73% (7/51; gRNA 1) and 19.05% (4/21; gRNA 2) of the targeted embryos, only the wild-type allele was observed, of which the majority (85.71%; 6/7) showed integrity of the targeted chromosome. Remarkably, for both designs, only in one of these embryos (1/7; gRNA 1 and 1/4; gRNA2) could repair template use be detected. This suggests that alternative repair events have occurred. Next, various genetic events within the same embryo were detected after single-cell analysis of four embryos.

CONCLUSION

Our results suggest the occurrence of mosaicism and complex repair events after CRISPR/Cas9 DSB induction where chromosomal integrity is predominantly contained.

Live birth rate per transfer is not impacted by the proportion of smooth endoplasmatic reticulum aggregates oocytes

BACKGROUND

Despite the data published to date, prognostic factors and the clinical impact of ICSI cycles with smooth endoplasmatic reticulum aggregates (SERa) positive oocytes remain unclear.

OBJECTIVE

Are the clinical outcomes of an ICSI cycle impacted by the proportion of oocytes with SERa?

MATERIALS AND METHODS

Retrospective study (2016-2019), including data from 2468 ovum pick-ups, performed in a tertiary university hospital. Cases are categorised based on the rate of SERa positive oocytes compared to the total number of MII oocytes: 0% (n=2097), <30% (n=262) and ≥30% (n=109).

MAIN OUTCOME MEASURES

Patient characteristics, cycle characteristics and clinical outcomes are compared between the groups.

RESULTS

Compared to SERa negative cycles, women with ≥30% SERa positive oocytes are older (36.2y vs. 34.5y, p<0.001), have lower anti-mullerian hormone levels (AMH) (1.6ng/ml vs. 2.3ng/ml, p<0.001), have received more gonadotropins (3227U vs. 2858IU, p=0.003), have a lower number of good quality day 5 blastocysts (1.2 vs. 2.3, p<0.001) and face more blastocyst transfer cancellation (47.7 vs. 23.7%, p<0.001). Women with <30% SERa positive oocytes are younger (33.8y, p=0.04), have higher AMH levels (2.6ng/ml, p<0.001), have more oocytes retrieved (15.1, p<0.001), have a higher number of good quality day 5 blastocysts (3.2, p<0.001) and have less transfer cancellations (14.9%, p<0.001) compared to SERa negative cycles A multivariate analysis shows no significant difference in cycle outcomes between the categories.

WHAT IS NEW?

Treatment cycles with ≥30% SERa positive oocytes are less likely to result in an embryo transfer when only non-SER oocytes are used. However, live birth rate per transfer is not affected by the proportion of SERa positive oocytes.

Characterization of ovarian tissue oocytes from transgender men reveals poor calcium release and embryo development, which might be overcome by spindle transfer

STUDY QUESTION

Can spindle transfer (ST) overcome inferior embryonic development of in vitro matured ovarian tissue oocytes (OTO-IVM) originating from testosterone-treated transgender men?

SUMMARY ANSWER

ST shows some potential to overcome the embryo developmental arrest observed in OTO-IVM oocytes from transgender men.

WHAT IS KNOWN ALREADY

OTO-IVM is being applied as a complementary approach to increase the number of oocytes/embryos available for fertility preservation during ovarian tissue cryopreservation in cancer patients. OTO-IVM has also been proposed for transgender men, although the potential of their oocytes remains poorly investigated. Currently, only one study has examined the ability of OTO-IVM oocytes originating from transgender men to support embryo development, and that study has shown that they exhibit poor potential.

STUDY DESIGN, SIZE, DURATION

Both ovaries from 18 transgender men undergoing oophorectomy were collected for the purposes of this study, from November 2020 to September 2022. The patients did not wish to cryopreserve their tissue for fertility preservation and donated their ovaries for research. All patients were having testosterone treatment at the time of oophorectomy and some of them were also having menses inhibition treatment.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Sibling ovaries were collected in either cold or warm medium, to identify the most optimal collection temperature. Cumulus oocyte complexes (COCs) from each condition were isolated from the ovarian tissue and matured in vitro for 48 h. The quality of OTO-IVM oocytes was assessed by calcium pattern releasing ability, embryo developmental competence following ICSI, and staining for mitochondrial membrane potential. In vitro matured metaphase I (MI) oocytes, germinal vesicle (GV) oocytes, and in vivo matured oocytes with aggregates of smooth endoplasmic reticulum (SERa) were donated from ovarian stimulated women undergoing infertility treatment and these served as Control oocytes for the study groups. ST was applied to overcome poor oocyte quality. Specifically, enucleated mature Control oocytes served as cytoplasmic recipients of the OTO-IVM spindles from the transgender men. Embryos derived from the different groups were scored and analysed by shallow whole genome sequencing for copy number variations (CNVs).

MAIN RESULTS AND THE ROLE OF CHANCE

In total, 331 COCs were collected in the cold condition (OTO-Cold) and 282 were collected in the warm condition (OTO-Warm) from transgender men. The maturation rate was close to 54% for OTO-Cold and 57% for OTO-Warm oocytes. Control oocytes showed a calcium releasing ability of 2.30 AU (n = 39), significantly higher than OTO-Cold (1.47 AU, P = 0.046) oocytes (n = 33) and OTO-Warm (1.03 AU, P = 0.036) oocytes (n = 31); both values of calcium release were similar between the two collection temperatures. Mitochondrial membrane potential did not reveal major differences between Control, OTO-Warm, and OTO-Cold oocytes (P = 0.417). Following ICSI, 59/70 (84.2%) of Control oocytes were fertilized, which was significantly higher compared to 19/47 (40.4%) of OTO-Cold (P < 0.01) and 24/48 (50%) of OTO-Warm oocytes (P < 0.01). In total, 15/59 (25.4%) blastocysts were formed on Day 5 in the Control group, significantly higher than 0/19 (0%) from the OTO-Cold (P = 0.014) and 1/24 (4.1%) in OTO-Warm oocytes (P = 0.026). Application of ST rescued the poor embryo development, by increasing the Day 5 blastocyst rate from 0% (0/19) to 20.6% (6/29) (P = 0.034), similar to that in the ICSI-Control group (25.4%, 15/59). A normal genetic profile was observed in 72.7% (8/11) of OTO-Cold, 72.7% (8/11) of OTO-Warm and 64.7% (11/17) of Control Day 3-Day 5 embryos. After ST was applied for OTO-IVM oocytes, 41.1% (7/17) of the embryos displayed normal genetic patterns, compared to 57.1% (4/7) among ST-Control Day 3-Day 5 embryos.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Due to the limited access to human oocytes and ovarian tissue, our results should be interpreted with some caution, as only a limited number of human oocytes and embryos could be investigated.

WIDER IMPLICATIONS OF THE FINDINGS

The results of this study, clearly indicate that OTO-IVM oocytes originating from transgender patients are of inferior quality, which questions their use for fertility preservation. The poor quality is likely to be related to cytoplasmic factors, supported by the increased blastocyst numbers following application of ST. Future research on OTO-IVM from transgender men should focus on the cytoplasmic content of oocytes or supplementation of media with factors that promote cytoplasmic maturation. A more detailed study on the effect of the length of testosterone treatment is also currently missing for more concrete guidelines and guidance on the fertility options of transgender men. Furthermore, our study suggests a potentially beneficial role of experimental ST in overcoming poor embryo development related to cytoplasmic quality.

STUDY FUNDING/COMPETING INTEREST(S)

A.C. is a holder of FWO grants (1S80220N and 1S80222N). A.B. is a holder of an FWO grant (1298722N). B.H. and A.V.S. have been awarded with a special BOF (Bijzonder Onderzoeksfonds), GOA (Geconcerteerde onderzoeksacties) and 2018000504 (GOA030-18 BOF) funding. B.H. has additional grants from FWO-Vlaanderen (Flemish Fund for Scientific Research, G051516N and G1507816N) and Ghent University Special Research Fund (Bijzonder Onderzoeksfonds, BOF funding (BOF/STA/202109/005)), and has been receiving unrestricted educational funding from Ferring Pharmaceuticals (Aalst, Belgium). The authors declare that they have no conflict of interest.

TRIAL REGISTRATION NUMBER

N/A.

Assisted oocyte activation does not overcome recurrent embryo developmental problems

STUDY QUESTION

Can recurrent embryo developmental problems after ICSI be overcome by assisted oocyte activation (AOA)?

SUMMARY ANSWER

AOA did not improve blastocyst formation in our patient cohort with recurrent embryo developmental problems after ICSI.

WHAT IS KNOWN ALREADY

The use of AOA to artificially induce calcium (Ca2+) rises by using Ca2+ ionophores (mainly calcimycin and ionomycin) has been reported as very effective in overcoming fertilization failure after ICSI, especially in patients whose Ca2+ dynamics during fertilization are deficient. However, there is only scarce and contradictory literature on the use of AOA to overcome embryo developmental problems after ICSI, and it is not clear whether abnormal Ca2+ patterns during fertilization disturb human preimplantation embryo development. Moreover, poor embryo development after ICSI has also been linked to genetic defects in the subcortical maternal complex (SCMC) genes.

STUDY DESIGN, SIZE, DURATION

This prospective cohort single-center study compared ICSI-AOA cycles and previous ICSI cycles in couples with normal fertilization rates (≥60%) but impaired embryonic development (≤15% blastocyst formation) in at least two previous ICSI cycles. In total, 42 couples with embryo developmental problems were included in this study from January 2018 to January 2021.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Of the 42 couples included, 17 underwent an ICSI-AOA cycle consisting of CaCl2 injection and double ionomycin exposure. Fertilization, blastocyst development, pregnancy, and live birth rates after ICSI-AOA were compared to previous ICSI cycles. In addition, the calcium pattern induced by the male patient's sperm was investigated by mouse oocyte calcium analysis. Furthermore, all 42 couples underwent genetic screening. Female patients were screened for SCMC genes (TLE6, PADI6, NLRP2, NLRP5, NLRP7, and KHDC3L) and male patients were screened for the sperm-oocyte-activating factor PLCZ1.

MAIN RESULTS AND THE ROLE OF CHANCE

We compared 17 AOA cycles to 44 previous ICSI cycles from the same patient cohort. After AOA, a total fertilization rate of 68.95% (131/190), a blastocyst development rate of 13.74% (18/131), a pregnancy rate of 29.41% (5/17), and a live birth rate of 23.53% (4/17) were achieved, which was not different from the previous ICSI cycles (76.25% (321/421, P-value = 0.06); 9.35% (30/321, P-value = 0.18), 25.00% (11/44, P-value = 0.75), and 15.91% (7/44, P-value = 0.48), respectively). Calcium analysis showed that patient's sperm induced calcium patterns similar to control sperm samples displaying normal embryo developmental potential. Genetic screening revealed 10 unique heterozygous variants (in NLRP2, NLRP5, NLRP7, TLE6, and PADI6) of uncertain significance (VUS) in 14 females. Variant NLRP5 c.623-12_623-11insTTC (p.?) was identified in two unrelated individuals and variant NLRP2 c.1572T>C (p.Asp524=) was identified in four females. Interestingly, we identified a previously reported homozygous mutation PLCZ1, c.1499C>T (p.Ser500Leu), in a male patient displaying impaired embryonic development, but not showing typical fertilization failure.

LIMITATIONS, REASONS FOR CAUTION

Our strict inclusion criteria, requiring at least two ICSI cycles with impaired embryo development, reduced cycle-to-cycle variability, while the requirement of a lower blastocyst development not influenced by a poor fertilization excluded couples who otherwise would be selective cases for AOA; however, these criteria limited the sample size of this study. Targeted genetic screening might be too restricted to identify a genetic cause underlying the phenotype of poor embryo development for all patients. Moreover, causality of the identified VUS should be further determined.

WIDER IMPLICATIONS OF THE FINDINGS

Strong evidence for AOA overcoming impaired embryonic development is still lacking in the literature. Thus far, only one article has reported a beneficial effect of AOA (using calcimycin) compared to previous ICSI cycles in this patient population, whilst two more recent sibling-oocyte control studies (one using calcimycin and the other ionomycin) and our research (using ionomycin) could not corroborate these findings. Although no major abnormalities have been found in children born after AOA, this technique should be reserved for couples with a clear Ca2+-release deficiency. Finally, genetic screening by whole-exome sequencing may reveal novel genes and variants linked to embryo developmental problems and allow the design of more personalized treatment options, such as wild-type complementary RNA or recombinant protein injection.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the Flemish Fund for Scientific Research (grant FWO.OPR.2015.0032.01 to B.H. and grant no. 1298722N to A.B.). A.C.B., D.B., A.B., V.T., R.P., F.M., I.D.C., L.L., D.S., P.D.S., P.C., and F.V.M. have nothing to disclose. B.H. reports a research grant from the Flemish Fund for Scientific Research and reports being a board member of the Belgian Society for Reproductive Medicine and the Belgian Ethical Committee on embryo research.

TRIAL REGISTRATION NUMBER

NCT03354013.

TEAD4 regulates trophectoderm differentiation upstream of CDX2 in a GATA3-independent manner in the human preimplantation embryo

STUDY QUESTION

What is the role of transcriptional-enhanced associate (TEA) domain family member 4 (TEAD4) in trophectoderm (TE) differentiation during human embryo preimplantation development in comparison to mouse?

SUMMARY ANSWER

TEAD4 regulates TE lineage differentiation in the human preimplantation embryo acting upstream of caudal-type homeobox protein 2 (CDX2), but in contrast to the mouse in a GATA-binding protein 3 (GATA3)-independent manner.

WHAT IS KNOWN ALREADY

Tead4 is one of the earliest transcription factors expressed during mouse embryo preimplantation development and is required for the expression of TE-associated genes. Functional knock-out studies in mouse, inactivating Tead4 by site-specific recombination, have shown that Tead4-targeted embryos have compromised development and expression of the TE-specific Cdx2 and Gata3 is downregulated. Cdx2 and Gata3 act in parallel pathways downstream of Tead4 to induce successful TE differentiation. Downstream loss of Cdx2 expression, compromises TE differentiation and subsequent blastocoel formation and leads to the ectopic expression of inner cell mass (ICM) genes, including POU Class 5 homeobox 1 (Pou5f1) and SRY-box transcription factor (Sox2). Cdx2 is a more potent regulator of TE fate in mouse as loss of Cdx2 expression induces more severe phenotypes compared with loss of Gata3 expression. The role of TEAD4 and its downstream effectors during human preimplantation embryo development has not been investigated yet.

STUDY DESIGN, SIZE, DURATION

The clustered regularly interspaced short palindromic repeats-clustered regularly interspaced short palindromic repeats (CRISPR)-associated genes (CRISPR-Cas9) system was first introduced in pronuclei (PN)-stage mouse zygotes aiming to identify a guide RNA (gRNA), yielding high editing efficiency and effective disruption of the Tead4 locus. Three guides were tested (gRNA1-3), each time targeting a distinct region of Exon 2 of Tead4. The effects of targeting on developmental capacity were studied in Tead4-targeted embryos (n = 164-summarized data from gRNA1-3) and were compared with two control groups; sham-injected embryos (n = 26) and non-injected media-control embryos (n = 51). The editing efficiency was determined by next-generation sequencing (NGS). In total, n = 55 (summarized data from gRNA1-3) targeted mouse embryos were analysed by NGS. Immunofluorescence analysis to confirm successful targeting by gRNA1 was performed in Tead4-targeted embryos, and non-injected media-control embryos. The downregulation of secondary TE-associated markers Cdx2 and Gata3 was used as an indirect confirmation of successful Tead4-targeting (previously shown to be expressed downstream of Tead4). Additional groups of gRNA1 Tead4-targeted (n = 45) and media control (n = 36) embryos were cultured for an extended period of 8.5 days, to further assess the developmental capacity of the Tead4-targeted group to develop beyond implantation stages. Following the mouse investigation, human metaphase-II (MII) oocytes obtained by IVM were microinjected with gRNA-Cas9 during ICSI (n = 74) to target TEAD4 or used as media-control (n = 33). The editing efficiency was successfully assessed in n = 25 TEAD4-targeted human embryos. Finally, immunofluorescence analysis for TEAD4, CDX2, GATA3 and the ICM marker SOX2 was performed in TEAD4-targeted (n = 10) and non-injected media-control embryos (n = 29).

PARTICIPANTS/MATERIALS, SETTING, METHODS

A ribonucleoprotein complex consisting of a gRNA-Cas9 mixture, designed to target Exon 2 of Tead4/TEAD4, was microinjected in mouse PN stage zygotes or human IVM MII oocytes along with sperm. Generated embryos were cultured in vitro for 4 days in mouse or 6.5 days in human. In mouse, an additional group of Tead4-targeted and media-control embryos was cultured in vitro for an extended period of 8.5 days. Embryonic development and morphology were assessed daily, during culture in vitro of mouse and human embryos and was followed by a detailed scoring at late blastocyst stage. Targeting efficiency following gRNA-Cas9 introduction was assessed via immunostaining and NGS analysis.

MAIN RESULTS AND THE ROLE OF CHANCE

NGS analysis of the Tead4-targeted locus revealed very high editing efficiencies for all three guides, with 100% of the mouse embryos (55 out of 55) carrying genetic modifications resulting from CRISPR-Cas9 genome editing. More specifically, 65.22% (15 out 23) of the PN zygotes microinjected with gRNA1-Cas9, which exhibited the highest efficiency, carried exclusively mutated alleles. The developmental capacity of targeted embryos was significantly reduced (data from gRNA1), as 44.17% of the embryos arrested at the morula stage (2.5 days post coitum), coincident with the initiation of TE lineage differentiation, compared with 8.51% in control and 12.50% in sham control groups. High-quality blastocyst formation rates (Grade 3) were 8.97% in the gRNA1-targeted group, compared with 87.23% in the media-control and 87.50% in the sham group. Immunofluorescence analysis in targeted embryos confirmed downregulation of Tead4, Cdx2, and Gata3 expression, which resulted from successful targeting of the Tead4 locus. Tead4-targeted mouse embryos stained positive for the ICM markers Pou5f1 and Sox2, indicating that expression of ICM lineage markers is not affected. Tead4-targeted embryos were able to cavitate and form a blastocoel without being able to hatch. Extended embryo culture following zona pellucida removal, revealed that the targeted embryos can attach and form egg-cylinder-like structures in the absence of trophoblast giant cells. In human embryos, Exon 2 of TEAD4 was successfully targeted by CRISPR-Cas9 (n = 74). In total, 25 embryos from various developmental stages were analysed by NGS and 96.00% (24 out of 25) of the embryos carried genetic modifications because of gRNA-Cas9 editing. In the subgroup of the 24 edited embryos, 17 (70.83%) carried only mutant alleles and 11 out of these 17 (64.70%) carried exclusively frameshift mutations. Six out of 11 embryos reached the blastocyst stage. In contrast to mice, human-targeted embryos formed blastocysts at a rate (25.00%) that did not differ significantly from the control group (23.81%). However, blastocyst morphology and TE quality were significantly compromised following TEAD4-targeting, showing grade C TE scores, with TE containing very few cells. Immunofluorescence analysis of TEAD4-targeted embryos (n = 10) confirmed successful editing by the complete absence of TEAD4 and its downstream TE marker CDX2, but the embryos generated retained expression of GATA3, which is in contrast to what we have observed and has previously been reported in mouse. In this regard, our results indicate that GATA3 acts in parallel with TEAD4/CDX2 towards TE differentiation in human.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

CRISPR-Cas9 germline genome editing, in some cases, induces mosaic genotypes. These genotypes are a result of inefficient and delayed editing, and complicate the phenotypic analysis and developmental assessment of the injected embryos. We cannot exclude the possibility that the observed differences between mouse and human are the result of variable effects triggered by the culture conditions, which were however similar for both mouse and human embryos in this study. Furthermore, this study utilized human oocytes obtained by IVM, which may not fully recapitulate the developmental behaviour of in vivo matured oocytes.

WIDER IMPLICATIONS OF THE FINDINGS

Elucidation of the evolutionary conservation of molecular mechanisms that regulate the differentiation and formation of the trophoblast lineage can give us fundamental insights into early implantation failure, which accounts for ∼15% of human conceptions.

STUDY FUNDING/COMPETING INTEREST(S)

The research was funded by the FWO-Vlaanderen (Flemish fund for scientific research, Grant no. G051516N), and Hercules funding (FWO.HMZ.2016.00.02.01) and Ghent University (BOF.BAS.2018.0018.01). G.C. is supported by FWO-Vlaanderen (Flemish fund for scientific research, Grant no. 11L8822N). A.B. is supported by FWO-Vlaanderen (Flemish fund for scientific research, Grant no. 1298722 N). We further thank Ferring Pharmaceuticals (Aalst, Belgium) for their unrestricted educational grant. The authors declare no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

No difference in cumulative live birth rates between cleavage versus blastocyst transfer in patients with four or fewer zygotes: results from a retrospective study

STUDY QUESTION

Is the cumulative live birth rate (CLBR) per oocyte collection cycle (OCC) comparable after cleavage-stage or blastocyst-stage transfer in combination with supernumerary blastocyst vitrification on Day 5 (D5) in patients with four or fewer zygotes on Day 1?

SUMMARY ANSWER

The CLBR in a fresh blastocyst-transfer or cleavage-stage transfer policy followed by vitrification on D5 is comparable in patients with four or fewer zygotes.

WHAT IS KNOWN ALREADY

Blastocyst transfer enhances the self-selection of the embryo and shortens the time to pregnancy in patients with normal or high ovarian response. Whether these advantages are also present in patients with a low ovarian response and/or a limited number of available zygotes is a continuous debate.

STUDY DESIGN, SIZE, DURATION

This was a retrospective, observational cohort study of 2359 consecutive OCCs between January 2014 and December 2018. According to a shift in transfer policy in our center, 571 OCCs had been scheduled for a fresh transfer on Day 3 (D3) and 1788 on D5. The D5 group was matched to the D3 group by propensity score (PS) matching according to multiple maternal baseline covariates. After PS matching, there were 571 OCCs in each group.

PARTICIPANTS/MATERIALS, SETTING, METHODS

OCCs scheduled for a D3 transfer (n = 571) or for a D5 transfer (n = 1788) were matched by PS matching in a 1:1 ratio accounting for potential confounding factors associated with CLBR. The model included patient characteristics, such as maternal age and cycle rank, as well as treatment characteristics such as GnRH analog regimen and ovarian response. Embryological variables included the number of zygotes and the number of 6- to 7- and 8-cell embryos on D3. The delivery outcomes of the fresh treatment cycle and the consecutive vitrified-warmed embryo transfers were analyzed up to the first live birth. The primary endpoint of this study was CLBR per OCC. Secondary outcomes were live birth rate per fresh transfer and embryo implantation rate per transferred embryo.

MAIN RESULTS AND THE ROLE OF CHANCE

The CLBR per OCC was comparable between the D5 and D3 groups (16.8% versus 17.7%, respectively, P = 0.600). Live birth rates per OCC did not differ between a cleavage-stage transfer and blastocyst-stage transfer policy (15.2% versus 12.4%, respectively, P = 0.160). In the D5 group, 201 cycles did not result in a blastocyst to perform an embryo transfer or cryopreservation; in the D3 group, only 59 cycles did not have an embryo transfer because of poor embryo quality (35.2% versus 10.3%, respectively; P < 0.001). A significantly higher number of fresh double embryo transfers were performed in the D3 group compared to D5 (23.8% versus 7.0%, respectively, P < 0.001).

LIMITATIONS, REASONS FOR CAUTION

Although adjusted for important confounders in the PS matching, BMI and embryo quality of the transferred embryo(s) were not taken into account. This study is limited by its retrospective design and is a single-center study, which may limit the generalizability of our findings.

WIDER IMPLICATIONS OF THE FINDINGS

The CLBR in a fresh blastocyst-transfer or cleavage-stage transfer policy followed by vitrification on D5 is comparable. A fresh embryo transfer on D3 can still be considered in patients with a poor ovarian response and/or limited number of zygotes when combined with blastocyst vitrification without impacting the overall CLBR of the cycle.

STUDY FUNDING/COMPETING INTEREST(S)

No external funding was obtained for this study. There are no conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

This retrospective study was approved by the local ethical committee at Ghent University Hospital (B 670201731234).

O-216 CRISPR/Cas9 mediated knock-out (KO) reveals a divergent role for trophectoderm markers GATA2/3 in the mouse and human preimplantation embryo

Study question

What is the effect of CRISPR/Cas9-mediated KO of trophectoderm (TE) markers GATA2/3 on embryo development and lineage commitment in both mouse and human preimplantation embryos?

Summary answer

CRISPR/Cas9-mediated KO of GATA2/3 points to interspecies differences in TE regulation and potential cross-talk between trophectoderm and inner cell mass (ICM) in mouse preimplantation embryos.

What is known already

GATA3 and its isoform GATA2 are major TE markers regulating the first lineage segregation, operating downstream of the HIPPO-pathway. Although recent evidence suggests that the HIPPO-pathway is conserved across mouse and human, it is unknown whether GATA2/3 share similar interspecies function during preimplantation development. GATA3 RNA depletion experiments in mouse embryos revealed a compensatory upregulation of GATA2, that potentially masked the observed phenotype. Upon double KO (DKO), the phenotype appeared more severe, as embryos were unable to cavitate. However, the precise effect of the (D)KO on embryo development was not investigated thoroughly, and should be expanded towards human preimplantation embryos.

Study design, size, duration

Mouse embryonic stem cells (mESCs), mouse zygotes and donated human spare oocytes were targeted. CRISPR/Cas9 ribonucleoprotein complexes, either targeting Gata3/GATA3, Gata2 or both, were delivered via nucleofection, electroporation or co-injected with sperm, in mESCs, mouse zygotes or human oocytes, respectively. Appropriate non-targeted control groups were included. Morphological analysis, immunofluorescence and next-generation sequencing were applied to check for gene editing efficiency and the impact of KO on embryonic development.

Participants/materials, setting, methods

The targeted embryos and controls were cultured for 4.5 (mouse) or 6.5 days (human) in vitro. They were stained for different developmental markers, including TEAD4 and CDX2 (TE), OCT4 and SOX2 (early ICM), NANOG (epibast, EPI) and SOX17 (hypoblast, PrE). Immunostaining was used to determine cell number, TE/ICM fraction, marker localization and fluorescence intensity. Embryos were subjected to genetic analysis to determine on-target efficiency, while in silico predicted off-target sites were evaluated in targeted mESCs.

Main results and the role of chance

GATA3 KO mouse embryos exhibited morula arrest (94%; n = 16). All GATA3-edited mouse embryos exhibited a reduction of CDX2-positive cells. From the 12 full KO embryos, four showed a decreased number of NANOG-positive blastomeres. No effect was observed for TEAD4 and OCT4. Complete KO morulas were devoid of SOX2 expression.

GATA2 KO mouse embryos could still form blastocysts (19% morula arrest, n = 21 embryos), even when harboring 100% frameshift mutations. KO did not noticeably influence cell number nor the expression of GATA3 or NANOG.

GATA2/3 DKO mouse embryos could still form blastocysts (38% morula arrest, n = 21), showing a milder phenotype compared to GATA3 KO embryos. In the presumed DKO blastocysts, the whole ICM is NANOG-positive and increased in cell number. SOX2 expression was still retained in the ICM, but presumed polar TE was also SOX2-positive.

Three out of four GATA3 KO human embryos harboring 100% frameshift mutations, were surprisingly able to form blastocysts. In one embryo, no morphological TE could be formed, while the others showed one or two CDX2-positive cells in TE. No effect was observed for TEAD4 and OCT4. In addition, all KO embryos displayed an increase in ICM/TE fraction. Some outer cells in KO blastocysts were NANOG-positive.

Limitations, reasons for caution

CRISPR/Cas9 is limited by the occurrence of mosaicism (more than one genotype present in an embryo) and potential off-target editing, which we will assess at in silico predicted off-target sites via NGS in mESCs. The observations of the study will be consolidated by increasing the sample size, especially in human.

Wider implications of the findings

Gene editing studies enable us to unravel the molecular interactions that are required for human preimplantation development. Obtaining novel insights into the molecular networks of the GATA transcription factor family could significantly improve our understanding of several pregnancy-related complications related to trophectoderm specification, such as early miscarriage or preeclampsia.

Trial registration number

NA

P-457 Spindle transfer rescues poor embryo development of in vitro matured ovarian tissue oocytes from transgender men

Study question

Could collection temperature and spindle transfer (ST) potentially improve development of embryos derived from in vitro matured (IVM) ovarian tissue oocytes (OTO) of transgender men?

Summary answer

Spindle transfer, but not collection temperature, significantly improved embryo development of OTO-IVM oocytes from transgender men.

What is known already

For transgender men, the fertility preservation strategy of ovarian stimulation may interfere with the desired masculine characteristics and enhance gender dysphoria. Alternatively, ovarian tissue oocytes collected ex vivo could serve as potential gametes, not requiring ovarian stimulation. Oocytes can be collected during gender affirming surgery, matured, and vitrified. Ovarian tissue oocyte in vitro maturation (OTO-IVM) has successfully been used for cancer patients, as live births have been reported. OTO-IVM in transgender men demonstrated sufficient maturation rates and survival following vitrification. Nevertheless, a decreased fertilization potential of these oocytes and severely compromised embryonic development have been observed.

Study design, size, duration

Patients between 18-24 years were recruited for this study from November 2020 to September 2021. Ovaries from 14 transgender men were collected in either cold (4oC, OTO-Cold) or warm (37oC, OTO-Warm) collection medium, to verify the best collection method. Following ovarian manipulation, cumulus oocyte complexes (COCs) were harvested from spent medium and underwent maturation for 48hrs. ST was performed to overcome inferior fertilization and embryonic development.

Participants/materials, setting, methods

Injected IVM oocytes underwent calcium imaging or were monitored for embryonic developmental potential. In vitro matured GV (germinal vesicle), MI (metaphase I) and in vivo matured oocytes with clusters of smooth endoplasmic reticulum (SERa) served as controls and cytoplasmic recipients for ST. OTO-IVM or control oocytes were used as spindle donors (ST-OTO or Control-ST respectively). Genetic analysis was performed to detect chromosomal abnormalities in embryos from all groups.

Main results and the role of chance

In total, we collected 252 OTO-Cold and 230 OTO-Warm oocytes, showing similar maturation rates (53%). For calcium imaging, 39 control, 33 OTO-cold and 31 OTO-warm oocytes were analysed, determining the product of amplitude per frequency, in arbitrary units (AU). The average value for control oocytes was 2.30AU, significantly higher than OTO-Cold (1.47AU, p=0.046) and OTO-Warm oocytes (1.03AU, p=0.036). Calcium release was similar between OTO-Cold and OTO-Warm oocytes. Following ICSI, 19/47 OTO-Cold and 24/48 OTO-Warm oocytes normally fertilized, significantly lower than the control group (42/52) (p &lt; 0.001 and p = 0.001 respectively). Blastocyst formation was significantly higher in control oocytes (13/42,31%) when compared to OTO-Cold (1/19, p=0.027) and OTO-Warm (2/24, p=0.035). No statistically significant difference in fertilization rate and embryo development was detected between OTO-Cold and OTO-Warm oocytes. ST was performed to overcome poor embryo development in the OTO-Cold group. Following ST, 12/19 ST-OTO-Cold and 24/38 Control-ST oocytes were normally fertilized. Blastocyst development was similar between the two groups (4/12 and 7/24 respectively), but significantly higher than blastocyst development in OTO-Cold ICSI oocytes (p = 0.038 and p = 0.045). Genetic analysis revealed that 4/10 OTO-Cold, 4/11 OTO-Warm, 4/11 ICSI control, and 4/7 Control-ST embryos were chromosomally abnormal while 6/8 OTO-ST were abnormal, and 2/8 showed a suggestive low-grade mosaicism.

Limitations, reasons for caution

A major limitation of our study is the lack of ovaries from cis women. Control oocytes used in this study originate from infertility patients that underwent ovarian stimulation. High abnormality rate in ST-OTO embryos might be concerning for the safety of ST, but the number of embryos analysed is limited.

Wider implications of the findings

Our data indicate that OTO-IVM oocytes from transgender men display poor cytoplasmic quality, demonstrated by embryonic arrest and calcium imaging. ST was able to overcome poor embryo development, and it could be of interest to use freshly donated oocytes as cytoplasmic recipients for this.

Trial registration number

Not applicable

O-075 Implicit bias in diagnosing mosaicism amongst preimplantation genetic testing providers: results from a large multicenter analysis of 36395 blastocysts

Study question

Does the diagnosis of mosaicism affect ploidy rates across different providers offering preimplantation genetic testing for aneuploidies (PGT-A)?

Summary answer

Our analysis of 36395 blastocyst biopsies across 8 genetic testing laboratories revealed that euploidy rates were significantly higher in providers reporting low rates of mosaicism.

What is known already

Diagnoses consistent with chromosomal mosaicism have emerged as a third category of possible options for embryo ploidy outcomes in PGT-A. However, diagnosing mosaicism using current PGT-A platforms remains hindered by several biological and technical factors. This has led to substantial variability in mosaicism rates amongst genetic testing laboratories. Furthermore, reservations regarding the clinical value of diagnosing mosaicism have led to varying practices in reporting mosaic calls amongst providers. Critically, it remains unknown whether these differences impact the number of euploid embryos available for transfer. Ultimately, this may significantly affect clinical outcomes, with important implications for PGT-A patients.

Study design, size, duration

Retrospective, international, multicenter cohort study of 10875 PGT-A cycles conducted between October 2015 and October 2021. A total of 18 IVF centers associated with 8 PGT-A providers, across 5 countries and 3 continents participated in the study, which included 36395 blastocysts, tested using trophectoderm biopsy and next generation sequencing (NGS). Both autologous and donation cycles were assessed. Preimplantation genetic testing for structural rearrangements (PGT-SR) cycles were excluded from the analysis.

Participants/materials, setting, methods

Ploidy rates were analyzed using multilevel mixed linear regression. Providers were categorized (A to H), with the most frequent provider used as the reference for statistical analysis. Analyses were adjusted for maternal age, paternal age, donor status, number of embryo biopsied and day of biopsy, as appropriate. The overall significance of categorical variables in the regression models was tested using a Chi-squared test. P-values &lt;0.05 were considered significant. Data analysis was performed using STATA, v.15.0.

Main results and the role of chance

The mean maternal age(+SD) across all providers was 36.9(±5.1). As expected, maternal age and day of biopsy had a significant impact on euploidy rates (p &lt; 0.0001). Mosaicism rates were associated with PGT-A provider and independent of all other parameters (maternal age, paternal age, donor status, number of embryos biopsied and day of biopsy). Out of the 8 providers, 7 reported chromosomal mosaicism. Amongst these 7 providers, the rate of mosaic calls varied from 2.9% to 23.9%. After adjusting for confounders, two providers reported significantly higher mosaicism rates compared to the reference (4.2%): Provider-C 10.4% (OR = 2.43, 95%CI: 1.84-4.25) and Provider-F 23.9% (OR = 4.47, 95%CI: 2.92-6.86), while euploidy and aneuploidy rates did not differ. Conversely, the chance of diagnosing mosaicism was lower in Provider-B (OR = 0.34, 95%CI: 0.22-0.54) and Provider-E (OR = 0.59, 95%CI: 0.38-0.90). Here, aneuploidy rates were comparable to the reference, yet the chance of diagnosing a euploid embryo was significantly higher: Provider-B (OR = 2.38, 95%CI: 1.87-3.03) and Provider-E (OR = 1.62, 95%CI: 1.28-2.05). Compared to the reference, euploidy rates were also higher when mosaicism was not reported: 53.5% vs. 44.2% (OR = 2.04, 95% CI: 1.60-2.59). Moreover, the chance of having at least one euploid blastocyst available for transfer significantly increased when mosaicism was not diagnosed (OR = 1.30, 95%CI: 1.13-1.50).

Limitations, reasons for caution

Due to the retrospective nature of the study, associations can be ascertained, however causality cannot be established. Certain parameters were not available in the dataset, therefore full elucidation of all potential confounders accounting for the variability may not be possible.

Wider implications of the findings

Our findings highlight the significant impact of the genetic testing provider on PGT-A results. We demonstrate that reporting mosaicism primarily comes at the expense of euploid diagnoses, raising concerns regarding the accuracy of mosaicism predictions and their impact on clinical outcomes. Moving forward, greater standardization amongst providers will be essential.

Trial registration number

NA

O-159 Uniform communication by nurses and midwives in anticipation of an IVF treatment

Study question

How do patients perceive the pre-IVF treatment communication by the nursing and midwifery team and how do they evaluate implemented optimization?

Summary answer

Patient satisfaction with the pre-IVF treatment communication by the nursing and midwifery team improved from 86% to 98% after implementation of standardized written patient information.

What is known already

Nurses are the main point of contact for patients undergoing medically assisted reproduction techniques (Applegarth et al., 2008). Morris (2001) suggested that infertility nurses could more specifically be involved in informative counselling in anticipation of the fertility treatment. Specific training for nurses and midwives would be required in order to achieve that central role in effective fertility counselling (Applegarth et al., 2012). However, little has been published in peer reviewed literature on how to assess and improve these pre-IVF treatment information sessions.

Study design, size, duration

The pre-IVF communication by the nurse/midwife was assessed by female patients with a self-developed questionnaire (cohort 1). The nursing and midwifery team was subsequently informed about the results of the questionnaire and efforts were undertaken to optimise future patient communication. Four years later, a follow-up questionnaire assessed patient satisfaction about the intervention (cohort 2). Each cohort comprised fifty patients and nurses and midwives were blinded for patient participation to the study.

Participants/materials, setting, methods

The study was performed at an academic fertility centre and was approved by the Investigational Review Board. Data were collected with SurveyMonkey (pre intervention) and REDCap (post intervention). A descriptive analysis of the cohorts and patient feedback was performed. The intervention consisted of (1) the optimization of patient information documents if needed (2) providing a training to the nursing and midwifery staff, and (3) a follow-up questionnaire in a second cohort of female fertility patients.

Main results and the role of chance

The first questionnaire revealed that overall, patients were satisfied with the informative counselling session in anticipation of the IVF treatment. However, some patients indicated that they received a lot of information at once and that specific information that was of relevance for the further treatment (e.g. oocyte pick-up) was sometimes missed. Also, the data showed that not all patients received the same information. Therefore, all information that patients needed during an IVF treatment was gathered into a patient binder. It was supplemented with a timeline of the whole IVF trajectory, QR codes to movies explaining the administration of medication, and answers to common patients’ questions. It was possible to individualize the content of the binder per patient. Ideally, patients received this binder before the informative counselling session so they could read the content in advance. The binder was developed by a member of the nursing and midwifery team and was reviewed by the medical, laboratory, and administrative staff. Then, the nursing and midwifery team was trained on the use of the patient binder. The follow-up questionnaire revealed that patient satisfaction with the pre-IVF treatment counselling was 98% after the optimization of patient documentation (compared to 86% before the optimization).

Limitations, reasons for caution

Eligible patients were recruited by the treating physician. As no records were kept of the number of solicited patients for this study, no assessment of the response rate is possible. The cohorts were self-selected and limited in size and could therefore not reflect the general patient population.

Wider implications of the findings

A patient questionnaire and follow-up is a useful tool for a centre specific assessment and improvement of pre-IVF nurse/midwife communication with patients. Clinics could make efforts to invest in complete and written information and ask colleagues of the nursing and midwifery team to be involved in its creation.

Trial registration number

NCT04420169

P-274 Cycles with a high proportion of smooth endoplasmatic reticulum aggregates oocytes have a higher risk of transfer cancellation, but similar clinical outcomes after embryo transfer

Study question

Are the clinical outcomes of an ICSI cycle impacted by the proportion of oocytes with smooth endoplasmatic reticulum aggregates (SERa)?

Summary answer

In terms of fertilization, blastocyst formation and live birth there is no difference between SERa- and SERa+ cycles, regardless of the proportion of SERa+ oocytes.

What is known already

It is not certain yet whether the presence of oocytes with SERa may impact the clinical outcome of an ICSI cycle. The majority of studies compare the outcome of SERa positive (SERa+) versus SERa negative (SERa-) cycles. It is not clear whether the proportion of SERa+ oocytes may play a role on cycles overall outcome, and which patients are at risk of harvesting a higher proportion of SERa+ oocytes. Limited data suggests that the duration of stimulation, the total dose of gonadotropins, the serum hormone levels and the number of oocytes are positively correlated with the presence of SERa+ oocytes.

Study design, size, duration

Retrospective study (2016-2019), including data from 2468 ovum pick-ups, performed in a tertiary university-based referral center. Results from fresh plus cryopreserved embryo transfers are included. In total, 2097 SERa- and 371 SERa+ cycles are included in the analysis.

Participants/materials, setting, methods

Cases are categorized based on the rate of SERa+ oocytes compared to the total number of metaphase II oocytes: SERa- (N = 2097), low SERa + (&lt;30%) (N = 262), and high SERa + (≥30%) (N = 109). Baseline patient characteristics, treatment cycle parameters and clinical outcome per cycle are compared between the groups. According to the local protocol, SERa+ oocytes are not used for ICSI.

Main results and the role of chance

Women with high SERa+ proportion are older (36.15y for the SERa+ group vs. 34.49y for the high SERa- group, p &lt; 0.001), have lower anti mullerian hormone levels (AMH) (1.60ng/ml vs. 2.28ng/ml, p &lt; 0.001), received a higher total dose of gonadotropins (3227.01IU vs. 2858IU, p = 0.003), have fewer oocytes retrieved (9.13 vs. 11.08, p &lt; 0.001), have a lower number of good quality day 5 blastocysts (1.17 vs. 2.33, p &lt; 0.001) and face more often transfer cancellation (23.7% vs. 47.7%, p &lt; 0.001).

Compared to women with SERa- cycles, women with &lt;30% SERa oocytes are younger (33.76y, p = 0.04), have higher AMH levels (2.56ng/ml, p &lt; 0.001), have more oocytes retrieved (15.11, p &lt; 0.001), have a higher number of good quality day 5 blastocysts (3.17, p &lt; 0.001) and less transfer cancellations (14.9%, p &lt; 0.001).

A multivariate regression model adjusted for age, progesterone level at ovulation trigger and the type of pituitary suppression shows that cycles with a high proportion of SERa+ still have a lower amount of day 5 blastocysts (p &lt; 0.001), a higher chance of transfer cancellation (p &lt; 0.001), but no difference in the amount of retrieved oocytes (p = 0.097), fertilization (p = 0.813), blastocyst formation rate (0.975), implantation (p = 0.105) and live birth rate (p = 0.615).

Limitations, reasons for caution

The SERa+ oocytes in this analysis were not used for ICSI, which could have affected the result between SERa+ and SERa- cycles.

Wider implications of the findings

A low proportion of SERa+ oocytes (&lt;30%) is common in young and high responders, without hampering clinical outcome. Contrary, &gt;30% SERa+ oocytes leads to a higher risk of transfer cancellation, when these oocytes are not used for ICSI. Therefore, the inclusion of SERa+ oocytes for ICSI should be further investigated.

Trial registration number

not applicable

P-196 Assessing human embryo implantation competence through analysis of extracellular vesicles and their contents

Study question

Could extracellular vesicles (EVs) derived from spent media serve as a non-invasive quality marker for embryo implantation and pregnancy?

Summary answer

EVs isolated from spent media derived from human blastocysts that either did or didn’t establish a pregnancy after transfer differ in size, concentration, miRNA expression.

What is known already

EVs are important for communication from one cell to another, influencing the translation of genes to proteins. They play a regulating role during biological processes, including pregnancy. We hypothesized that EVs released by a high-quality human embryo, which has the potential to create a pregnancy after the transfer, differ from EVs released by poor quality non-implanting embryos.

Study design, size, duration

Patients scheduled for a fresh single blastoycst transfer in IVF/ICSI cycles using own gametes consented to sampling of spent culture media (n = 102). Spent media from the transferred blastocyst (25 μl) were collected from implanted (hCG+/ET) (n = 45) and non-implanted (hCG-/ET) (n = 51). Spent media from degenerated embryos (n = 21) were collected from 6 patients. Media samples were pooled randomly into three replicates for each group (implanted (I), non-implanted (NI), degenerated (DG)).

Participants/materials, setting, methods

Extracellular vesicles were isolated by qEV single size exclusion column(SEC):a maximum of 200 µl of implanted or non-implanted or degenerated spent media was loaded onto the qEV SEC. Identification and characterization of EVs was performed by nanoparticle tracking analysis, transmission electron microscopy, and western blotting (CD9, CD63). Next, EV-RNA isolation was performed on these three groups (three replicates from each group) by Norgen Biotek Exosomal RNA Purification Kit, followed by RT-qPCR, and further data analysis.

Main results and the role of chance

Extracellular vesicles isolated from the SEC column are referred to as I-EVs, NI –EVs, and DG-EVs (implanted, non-implanted, and degenerated, respectively). Western blot confirmed the presence of EV-specific markers (CD63, CD9) in all EV samples (I-EVs, NI-EVs, and DG-EVs). By NTA, a higher particle concentration was observed in I-EVs (2.69±1.9 × 1010 particles/mL) compared to NI-EVs (6.13±0.2 × 1010 particles/mL) (p &lt; 0.05), whereas DG-EVs particle concentration (4.97±0. 2 × 109 particles/mL) was significantly (P &lt; 0.01). I-EVs were also characterized by a larger particle size with an average mean diameter of 180.3±5.4 nm, whereas NI-EVs displayed a smaller particle size with a mean diameter of 141.5±2.5 nm (p &lt; 0.05). TEM confirmed the presence of larger-sized vesicles in I-EVs (≥ 200 nm) compared with NI and DG samples. During earlier work in EVs from bovine blastocysts we found miR-378a-3p to be typically present in blastocyst EVs, with a prominent role in the hatching process of the blastocyst. Here, we compared miR-378a-3p expression levels by RT-qPCR in I-EVs vs. NI-EVs vs DG-EVs. Higher expression of miR-378a-3p was identified in NI-EVs and I-EVs, compared to DG-EVs (log2fc= 30.10, log2fc = 8.94 p &lt; 0.001 respectively), but was not correlated with implantation rate.

Limitations, reasons for caution

Currently, the methodology is unable to study EVs from a single droplet of spent media, hence pooling of the samples is necessary. As a consequence, data on EV-miRNA from individual blastocyst is lost.

Wider implications of the findings

Our data demonstrated that EVs and their cargo (miRNAs) have potential to be used as a non-invasive method to predict embryo implantation:miR-378a-3p has been associated with hatching in bovine embryos, but was not related with human implantion. Other embryo-derived miRNAs may be tested as a possible biomarker for human pregnancy.

Trial registration number

EC 2018/0266 – B670201835577

P-238 Treatment options to overcome impaired fertilization and embryonic development caused by an oocyte-related deficiency in the Patl2-/- mouse model

Study question

Can assisted oocyte activation (AOA) or spindle transfer (ST) overcome the lower fertilization and blastocyst rates observed in the Patl2-/- mouse model?

Summary answer

ST, but not AOA, has the potential to restore both normal fertilization and blastocyst rates in a mouse model with an oocyte-related deficiency.

What is known already

PATL2 is an RNA-transcriptional repressor involved in the regulation of maternal mRNAs during oocyte maturation. Mutations in PATL2 have been detected in patients with oocyte maturation arrest, reduced fertilization and embryo developmental arrest. Consequently, these patients are mostly referred to oocyte donation. Both AOA, inducing artificially calcium oscillations by calcium ionophores, and ST, replacing bad-quality oocyte cytoplasm with healthy cytoplasm, have been proposed to treat oocyte-related infertility. However, there is a lack of studies showing which oocyte-related infertility indications may benefit from which specific treatment. The Patl2-/- mouse model offers a unique opportunity to study the efficiency of these treatments.

Study design, size, duration

An experimental study using C57BL/6NTac-Patl2tm1a mice was conducted between April to December 2021. Breeding of heterozygous C57BL/6NTac-Patl2tm1a mice resulted in a total of 156 pups, from which 22 were homozygous C57BL/6NTac-Patl2tm1a ( Patl2-/-) females. Metaphase II (MII) oocytes were collected from Patl2-/- (test group) and Patl2+/+ (control group) females and used to evaluate different oocyte quality markers, as well as the efficiency of AOA and ST treatments to improve the oocyte-related subfertility observed in Patl2-/- mice.

Participants/materials, setting, methods

Four- to 12-week-old mice were subjected to ovarian hyperstimulation and oocyte collection, where oocyte maturation was assessed. Afterwards, MII oocytes were used to evaluate oocyte diameter, spindle abnormalities, activation rate (AR) and blastocyst rate (BR) after PIEZO-ICSI and calcium releasing capacity after SrCl2 exposure. Finally, Patl2-/- MII oocytes were treated with AOA, by direct exposure to SrCl2, or ST treatment, by transferring the Patl2-/- spindle to Patl2+/+ cytoplasm (previously enucleated) followed by SrCl2 exposure.

Main results and the role of chance

No difference in the number of cumulus-oocyte complexes (COCs) and mature MII oocytes was observed between 6 Patl2-/- mice (128 MII/159 COCs) and 5 Patl2+/+ mice (108 MII/132 COCs). However, Patl2-/- MII oocytes showed a significantly lower cytoplasm diameter (68,11 ± 2,25, n = 79) than Patl2+/+ oocytes (75,19 ± 2,09, n = 77, p-value&lt;0,001), suggesting that Patl2 affects oocyte growth but does not seem to affect oocyte maturation. Nuclear maturity was not compromised either, as a similar percentage of oocytes with normal spindle was observed in Patl2-/- (48,4%, 15/31) and Patl2+/+ MII oocytes (50%, 18/36). Activation and blastocyst rates after PIEZO-ICSI were lower in Patl2-/- (AR = 45,5%, 5/11 and BR = 20,0%, 1/5) than in Patl2+/+(AR = 75,0%, 21/28 and BR = 52,4%, 11/21).

In addition, total calcium released during oocyte activation after SrCl2 exposure was not different between Patl2-/- (AxF=6,88 AU, n = 30) and Patl2+/+ MII oocytes (AxF=5,04 AU, n = 28, p-value=0,087). In line with these results, AOA treatment did not improve activation and blastocyst rates in Patl2-/- oocytes (AR = 66,7%, 44/66 and BR = 45,5%, 20/44) compared to Patl2+/+ oocytes (AR = 96,5%, 110/114 and BR = 79,1%, 87/110, p-value&lt;0,001). Nonetheless, when performing ST using Patl2-/- as spindle donors and Patl2+/+ as cytoplasm recipients, activation (8/8, 100,0%) and blastocyst rate (6/8, 75,0%) were restored to normal values.

Limitations, reasons for caution

This study describes preliminary results and is limited by its small sample size. In addition, we did not identify an increased number of immature oocytes and spindle abnormalities in Patl2-/- female mice in contrast to previously published reports.

Wider implications of the findings

ST could be offered to treat PATL2- related female-infertility caused by a cytoplasmic deficiency, to increase both fertilization and blastocyst rates. AOA would not be beneficial for these patients as calcium releasing capacity of Patl2-/- oocytes does not seem to be affected, suggesting a deficiency independent from calcium releasing machinery.

Trial registration number

Not applicable

P-802 Distinct genetic impact of CRISPR/Cas9 gene correction in human embryos compared to induced pluripotent stem cells

Study question

Does CRISPR/Cas9 gene editing have a distinct genetic impact in human embryos compared to induced pluripotent stem cells (iPSCs)?

Summary answer

IPSCs display a difference in repair events, such as template usage, compared to the germline which indicates a distinct genetic impact by CRISPR/Cas9 gene editing.

What is known already

CRISPR/Cas9 is utilized to induce targeted DNA editing. To introduce specific changes, such as mutational correction, a DNA template is generally administered, stimulating homology-directed repair. Recent human germline editing studies aiming for mutational repair created a moderate amount of embryos which solely carried wild-type alleles. Remarkably, no template use was observed, but instead loss-of-heterozygosity (LOH) was demonstrated. This is the presence of only one (the wild-type) allele, either caused by gene conversion events using the wild type allele or chromosome loss. Up to date, no iPSCs studies have evaluated LOH events when attempting to correct a heterozygous mutation.

Study design, size, duration

A guide RNA targeting the mutant allele, and a repair template containing the wild-type allele and a synonymous variant to track template usage were designed. For iPSCs targeting, the components were nucleofected after which DNA was extracted from the whole well (n = 3) or from individual colonies (n = 33). For human embryo targeting, the components were injected simultaneously with sperm into donated spare oocytes (n = 32). DNA was extracted from embryos after 3-6 days of in vitro culture.

Participants/materials, setting, methods

Sperm and renal cells, from which the iPSCs were derived, were donated by a patient with a heterozygous base pair substitution in PLCZ1 (c.136-1G&gt;C) causing fertilization failure. To overcome fertilization failure, assisted oocyte activation was employed during ICSI. For the embryos, next-generation sequencing (NGS), short tandem repeat (STR) analysis and a whole genome single nucleotide polymorphism (SNP) assay were performed. For the iPSCs, NGS and a targeted SNP assay were carried out.

Main results and the role of chance

The genetic events in embryos originating from mutant sperm (n = 32) displayed following distribution: 19% showed the untargeted mutant allele, 56% showed additional mutagenesis and 25% showed only the wild-type allele. In the latter group, the template was never utilized, pointing to LOH. STR analysis indeed revealed LOH events of different lengths in these embryos. SNP analysis of one embryo, originating from mutant sperm but displaying the wild-type allele, did not demonstrate LOH (with a detection limit of 500bp). These findings suggest the occurrence of gene conversion, which rejects the formerly stated hypothesis that the observed LOH in human embryos can mostly be attributed to chromosome loss. In the iPSCs, whole-well (n = 3) and single colony (n = 33) data demonstrated a similar trend in genetic event distribution compared to the embryos, with the main difference that in 30% of the corrected reads/colonies, template use was observed. LOH was further analysed in nineteen single colonies. In all the colonies (3/3) corrected with the template, no LOH was present. When the colonies displayed additional mutagenesis, 7% (1/13) contained LOH events. In 33% (1/3) of the colonies showing only the wild-type allele (without signs of template use), LOH was observed.

Limitations, reasons for caution

SNP assays have a higher resolution compared to STR analysis, and enable distinction of LOH events between ‘gene conversion’ and ‘chromosome loss’. Therefore, more embryos and iPSC colonies will be analysed with SNP assays. However, informative SNPs define the resolution of our assay (currently 500 bp from Cas9 cut site).

Wider implications of the findings

Our results show that template usage seems to differ between human embryos and iPSCs, but that iPSCs do not solely rely on template use as well. This demonstrates that embryo experiments to study the genetic impact of CRISPR/Cas9 cannot fully be replaced by iPSCs experiments.

Trial registration number

Not Applicable

O-099 TEAD4 regulates trophectoderm differentiation upstream of CDX2 in human preimplantation embryos

Study question

What is the main pathway regulating trophectoderm (TE) differentiation during pre-implantation development in mouse versus human embryos?

Summary answer

TEAD4 is acting upstream of CDX2 and is involved in TE differentiation, as TEAD4-null human embryos exhibit compromised TE lineage differentiation.

What is known already

TEAD4 is the earliest transcription factor during early embryo development, required for the expression of TE-associated genes leading to successful TE differentiation and subsequent blastocoel formation in mouse. Functional knock-out studies in mouse, inactivating Tead4 by site-specific recombination have shown that Tead4-null embryos do not express TE specific genes, including Caudal-Type Homeobox Protein 2 (Cdx2) and GATA Binding Protein 3 (Gata3), but expression of inner cell mass (ICM)-specific genes, remains unaffected. Furthermore, ablation of Tead4 compromises embryonic development and subsequent blastocoel formation in mouse. The role of TEAD4, during human pre-implantation development has not been functionally characterized yet.

Study design, size, duration

CRISPR-Cas9 was introduced in mouse zygotes and editing efficiency was evaluated by next-generation sequencing (NGS) on 4.5dpc embryos (n = 55). Developmental kinetics were monitored in CRISPR-Cas9 targeted (n = 83), sham-injected (n = 26) and non-injected media-control (n = 51) mouse embryos. Immunofluorescence analysis was performed in Tead4 targeted (n = 57) and non-injected media-control embryos (n = 94). The same methodology was applied in human donated in vitro matured (IVM) metaphase-II (MII) oocytes, which were CRISPR-Cas9 targeted (n = 74) during ICSI or used as media-Control (n = 33).

Participants/materials, setting, methods

A gRNA-Cas9 mixture targeting exon 2 of Tead4/TEAD4 was microinjected in respectively mouse 2PN (pronuclear) stage zygotes, or human IVM MII oocytes along with the sperm. Generated embryos were cultured in vitro for 4 days in mouse or 6.5 days in human. Embryonic development and morphology were assessed daily, followed by a detailed scoring at the late blastocyst stage. Successful targeting following CRISPR-Cas9 introduction was assessed by immunostaining and NGS analysis of the targeted locus.

Main results and the role of chance

In mouse, we confirmed previous findings, as the developmental capacity of Tead4 targeted embryos was significantly reduced starting from the morula stage and blastocyst formation rates were 8.97% in the targeted group, compared to 87.23% in the control and 87.50% in the sham group, respectively. Immunofluorescence analysis of late morula and blastocyst stage embryos confirmed the absence of Tead4, Cdx2 and Gata3, resulting from the successful interruption of the Tead4 locus (n = 57). Exon 2 of TEAD4 was successfully targeted in human. In total, 21 embryos from various developmental stages were successfully NGS analyzed and 90,48% (19 out of 21) of the embryos carried genetic modifications as a result of CRISPR-Cas9 genome editing and seven blastocysts were identified carrying exclusively frameshift mutations. In contrast to mouse, the developmental capacity of human targeted embryos (25%) did not differ significantly from the control group (23%). However, the blastocyst morphology and quality were compromised in the targeted group showing mostly grade C TE scores, containing very few cells. Immunofluorescence analysis of targeted blastocysts (n = 6) confirmed successful editing by complete absence of TEAD4 and its downstream TE marker CDX2.

Limitations, reasons for caution

CRISPR-Cas9 germline genome editing results in multiple editing outcomes with variable phenotypic penetrance, the mosaic nature of which complicates the phenotypic analysis and developmental behaviour of the injected embryos.

Wider implications of the findings

Elucidation of the evolutionary conserved molecular mechanisms that regulate self-renewal of the trophoblast lineage can give us fundamental insights on early implantation failure.

Trial registration number

Not Applicable

P–429 Calcium analysis and embryonic development of in vitro matured oocytes from transgender men

Study question

Can oocytes isolated from transgender men after oophorectomy support embryonic development?

Summary answer

Embryo developmental arrest at 4–8cell stage (day 3 embryos) indicates poor quality of in vitro matured oocytes from transgender men.

What is known already

Gender affirming surgery for transgender men leads to permanent infertility, as it involves bilateral oophorectomy. Current approaches for fertility preservation, such as oocyte freezing following ovarian hyperstimulation, may interfere with the wanted masculine characteristics and enhance gender dysphoria. In vitro matured oocytes (IVM) isolated following oophorectomy have been proposed as a source of potential gametes to ensure fertility preservation for transgender men with a child wish. From previous studies, it has been shown that these oocytes are able to undergo maturation and display normal spindles, but their competence to be fertilized and support embryonic development has not been addressed yet.

Study design, size, duration

We evaluated the quality of in vitro matured oocytes isolated from ovaries of transgender men by applying calcium imaging and monitoring fertilization and embryonic development following intracytoplasmic sperm injection (ICSI). Ovaries were collected in cold (4oC) or warm (37oC) medium, to investigate the best collection procedure. So far, results from four transgender men have been included. Participants/materials, setting, methods: Ovaries from four transgender men undergoing testosterone treatment were collected after oophorectomy in cold or warm medium. Cumulus oocyte complexes (COCs) were isolated and cultured in maturation medium for 48hrs. Mature oocytes were injected with donated sperm and assessed either by calcium imaging, measuring the total calcium release following injection, or following embryonic development. Donated in vitro matured oocytes, germinal vesicle(GV) or metaphase I(MI) origin, from other patients undergoing IVF treatment were used as controls.

Main results and the role of chance

In total, 179 COCs were collected from ovaries (n = 8) of four transgender men. From the COCs collected in warm medium, 73/105(69%) survived and 33/73(45%) reached metaphase II (MII). Of 21 MII injected with sperm, 13/21(62%) fertilized, 9/21(43%) formed 2 pronuclei (PN), 8/9(89%) reached the 2-cell stage, 3/9(33%) reached 4–8cell stage but arrested. From 74 COCs isolated in cold medium, 57/74(77%) survived and 28/57(49%) matured. Of the 11 MII injected with sperm, 7/11(64%) fertilized, 6/11(54%) formed 2PN, 6/6(100%) reached the 2-cell stage, 4/6(67%) reached 4–8cell but arrested. In the control group, 10/13 oocytes injected with the same sperm sample, were normally fertilized (77%), 8/10(80%) reached the 2-cell stage, 7/10(70%) reached the 4–8cell stage and 4/10(40%) became blastocysts. From the warm, cold and control conditions, respectively 12,14 and 17 MII oocytes were used for calcium imaging. The product of amplitude and frequency of calcium peaks, representing total calcium release, was calculated. Oocytes showed an average release of 0.66AU and 1.69AU for the warm and cold condition, respectively. The average value for control oocytes was 2.19AU.

Limitations, reasons for caution

One major limitation of our study is the lack of ovaries from cis women as control group. Our control oocytes originated from women undergoing IVF treatment and have undergone ovarian stimulation. Furthermore, the number of oocytes analysed and number of patients per group was limited and is being increased.

Wider implications of the findings: Our data indicate that in vitro matured oocytes from transgender men ovaries display poor quality, as demonstrated by the poor embryonic development. In the future, we will apply nuclear transfer technology as a mean to overcome embryonic developmental arrest in this group of oocytes.

Trial registration number

Not applicable

O-090 Correcting a PLCζ mutation in the human germ line to overcome hereditary infertility

Study question

Can clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 gene editing result in the correction of a single base pair substitution that causes male infertility?

Summary answer

CRISPR/Cas9 administration during intracytoplasmic sperm injection (ICSI) leads to correction attempts of mutant phospholipase C zeta (PLCζ), howeverc loss-of-heterozygosity (LOH).

What is known already

Failed fertilization after ICSI can be caused by mutations in the sperm-related oocyte factor PLCζ which can be overcome by assisted oocyte activation (AOA). In this way, children may inherit the infertility-causing mutation. Mutation transmission can be overcome through CRISPR/Cas9 delivery during ICSI. In previous studies using CRISPR/Cas9 in the human germline for mutation correction, loss-of-heterozygosity (LOH, loss of the allele of one of the parents) was observed. Two different explanations were given, namely partial or complete paternal chromosomal loss or the correction of the mutation by using the maternal wild-type allele instead of the exogeneous supplied repair template.

Study design, size, duration

We injected a gRNA-Cas9 protein complex to target the PLCζ mutant allele, a repair template harboring the desired nucleotide substitution and an additional synonymous variant to track template usage, together with patient’s sperm. To overcome fertilization failure, AOA was applied during ICSI. After a culture period of maximal 6 days the embryos were collected. At day 3, some embryos were dissociated in individual blastomeres. The extracted DNA was analyzed through different genetic sequencing techniques.

Participants/materials, setting, methods

Donated sperm of a patient experiencing complete fertilization failure after routine ICSI, harboring a heterozygous base pair substitution in PLCZ1 (c.136-1G&gt;C), was utilized. Sperm was injected in donated in vitro matured oocytes or in vivo matured oocytes containing clusters of smooth endoplasmic reticulum. Next-generation sequencing was used to assess correction potential. Short tandem repeat (STR) and single nucleotide polymorphism (SNP) assays were used to determine whether the sperm contained the mutation and to evaluate LOH.

Main results and the role of chance

CRISPR/Cas9 injections had no significant impact (p &gt; 0.05) on embryonic development. Due to the heterozygous nature of the mutation, 47% (27/58) of the embryos originated from mutated sperm injection. The CRISPR components showed a high specificity with absence of insertions/deletions in 97% of the embryos originating from wild-type sperm (n = 31). Embryos originating from mutant sperm (n = 27) fall into three categories:(1) 22% showed the untargeted mutant allele, (2) 52% showed additional mutagenesis and (3) 26% showed the wild-type allele, which could be explained by correction. Mosaicism, defined as various editing events, was present in 17% (1), 21% (2) and 71% (3) of the embryos. The low occurrence of the synonymous variant, incorporated in the repair template, suggests that the template is not used during correction attempts. In only 29% (2/7) and 14% (1/7) of the ‘corrected embryos’, respectively long (&gt;18Mb) or medium width LOH (4Mb) was observed through STR analysis. SNP analysis in closer proximity showed in 71% (5/7) of the embryos LOH, even in the absence of LOH through STR, suggesting also the occurrence of short width LOH. These results will be studied in more detail before definitive conclusions can be made. Chromosomal LOH will be studied by ddRADseq.

Limitations, reasons for caution

The occurrence of mosaicism and LOH might complicate the use of traditional CRISPR/Cas9 in human embryos and should be studied in detail to draw definite conclusions on its potential future use. To this end, genomic data have been produced from both individual blastomeres and whole-embryos which will be further analyzed.

Wider implications of the findings

Our findings demonstrate caution to use CRISPR/Cas9 to correct mutations in the germ line. They seem to contradict other reports that show predominant lack of mosaicism and presence of long width LOH. A deeper evaluation will be undertaken to define the length and type of LOH in this study.

Trial registration number

Not Applicable

Comparative analysis of mouse and human preimplantation development following POU5F1 CRISPR/Cas9 targeting reveals interspecies differences

STUDY QUESTION

What is the role of POU class 5 homeobox 1 (POU5F1) in human preimplantation development and how does it compare with the mouse model?

SUMMARY ANSWER

POU5F1 is required for successful development of mouse and human embryos to the blastocyst stage as knockout embryos exhibited a significantly lower blastocyst formation rate, accompanied by lack of inner cell mass (ICM) formation.

WHAT IS KNOWN ALREADY

Clustered regularly interspaced short palindromic repeats-CRISPR associated genes (CRISPR-Cas9) has previously been used to examine the role of POU5F1 during human preimplantation development. The reported POU5F1-targeted blastocysts always retained POU5F1 expression in at least one cell, because of incomplete CRISPR-Cas9 editing. The question remains of whether the inability to obtain fully edited POU5F1-targeted blastocysts in human results from incomplete editing or the actual inability of these embryos to reach the blastocyst stage.

STUDY DESIGN, SIZE, DURATION

The efficiency of CRISPR-Cas9 to induce targeted gene mutations was first optimized in the mouse model. Two CRISPR-Cas9 delivery methods were compared in the B6D2F1 strain: S-phase injection (zygote stage) (n = 135) versus metaphase II-phase (M-phase) injection (oocyte stage) (n = 23). Four control groups were included: non-injected media-control zygotes (n = 43)/oocytes (n = 48); sham-injected zygotes (n = 45)/oocytes (n = 47); Cas9-protein injected zygotes (n = 23); and Cas9 protein and scrambled guide RNA (gRNA)-injected zygotes (n = 27). Immunofluorescence analysis was performed in Pou5f1-targeted zygotes (n = 37), media control zygotes (n = 19), and sham-injected zygotes (n = 15). To assess the capacity of Pou5f1-null embryos to develop further in vitro, additional groups of Pou5f1-targeted zygotes (n = 29) and media control zygotes (n = 30) were cultured to postimplantation stages (8.5 dpf). Aiming to identify differences in developmental capacity of Pou5f1-null embryos attributed to strain variation, zygotes from a second mouse strain-B6CBA (n = 52) were targeted. Overall, the optimized methodology was applied in human oocytes following IVM (metaphase II stage) (n = 101). The control group consisted of intracytoplasmically sperm injected (ICSI) IVM oocytes (n = 33). Immunofluorescence analysis was performed in human CRISPR-injected (n = 10) and media control (n = 9) human embryos.

PARTICIPANTS/MATERIALS, SETTING, METHODS

A gRNA-Cas9 protein mixture targeting exon 2 of Pou5f1/POU5F1 was microinjected in mouse oocytes/zygotes or human IVM oocytes. Reconstructed embryos were cultured for 4 days (mouse) or 6.5 days (human) in sequential culture media. An additional group of mouse-targeted zygotes was cultured to postimplantation stages. Embryonic development was assessed daily, with detailed scoring at late blastocyst stage. Genomic editing was assessed by immunofluorescence analysis and next-generation sequencing.

MAIN RESULTS AND THE ROLE OF CHANCE

Genomic analysis in mouse revealed very high editing efficiencies with 95% of the S-Phase and 100% of the M-Phase embryos containing genetic modifications, of which 89.47% in the S-Phase and 84.21% in the M-Phase group were fully edited. The developmental capacity was significantly compromised as only 46.88% embryos in the S-Phase and 19.05% in the M-Phase group reached the blastocyst stage, compared to 86.36% in control M-Phase and 90.24% in control S-Phase groups, respectively. Immunofluorescence analysis confirmed the loss of Pou5f1 expression and downregulation of the primitive marker SRY-Box transcription factor (Sox17). Our experiments confirmed the requirement of Pou5f1 expression for blastocyst development in the second B6CBA strain. Altogether, our data obtained in mouse reveal that Pou5f1 expression is essential for development to the blastocyst stage. M-Phase injection in human IVM oocytes (n = 101) similarly resulted in 88.37% of the POU5F1-targeted embryos being successfully edited. The developmental capacity of generated embryos was compromised from the eight-cell stage onwards. Only 4.55% of the microinjected embryos reached the late blastocyst stage and the embryos exhibited complete absence of ICM and an irregular trophectoderm cell layer. Loss of POU5F1 expression resulted in absence of SOX17 expression, as in mouse. Interestingly, genetic mosaicism was eliminated in a subset of targeted human embryos (9 out of 38), three of which developed into blastocysts.

LIMITATIONS, REASONS FOR CAUTION

One of the major hurdles of CRISPR-Cas9 germline genome editing is the occurrence of mosaicism, which may complicate phenotypic analysis and interpretation of developmental behavior of the injected embryos. Furthermore, in this study, spare IVM human oocytes were used, which may not recapitulate the developmental behavior of in vivo matured oocytes.

WIDER IMPLICATIONS OF THE FINDINGS

Comparison of developmental competency following CRISPR-Cas-mediated gene targeting in mouse and human may be influenced by the selected mouse strain. Gene targeting by CRISPR-Cas9 is subject to variable targeting efficiencies. Therefore, striving to reduce mosaicism can provide novel molecular insights into mouse and human embryogenesis.

STUDY FUNDING/COMPETING INTEREST(S)

The research was funded by the Ghent University Hospital and Ghent University and supported by the FWO-Vlaanderen (Flemish fund for scientific research, Grant no. G051516N), and Hercules funding (FWO.HMZ.2016.00.02.01). The authors declare no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

The effect of polymorphisms in FSHR and FSHB genes on ovarian response: a prospective multicenter multinational study in Europe and Asia

STUDY QUESTION

Does the presence of single nucleotide polymorphisms (SNPs) in the FSH receptor gene (FSHR) and/or FSH beta subunit-encoding gene (FSHB) influence ovarian response in predicted normal responders treated with rFSH?

SUMMARY ANSWER

The presence of FSHR SNPs (rs6165, rs6166, rs1394205) has a statistically significant impact in ovarian response, although this effect is of minimal clinical relevance in predicted normal responders treated with a fixed dose of 150 IU rFSH.

WHAT IS KNOWN ALREADY

Ovarian reserve markers have been a breakthrough in response prediction following ovarian stimulation. However, a significant percentage of patients show a disproportionate lower ovarian response, as compared with their actual ovarian reserve. Studies on pharmacogenetics have demonstrated a relationship between FSHR or FSHB genotyping and drug response, suggesting a potential effect of individual genetic variability on ovarian stimulation. However, evidence from these studies is inconsistent, due to the inclusion of patients with variable ovarian reserve, use of different starting gonadotropin doses, and allowance for dose adjustments during treatment. This highlights the necessity of a well-controlled prospective study in a homogenous population treated with the same fixed protocol.

STUDY DESIGN, SIZE, DURATION

We conducted a multicenter multinational prospective study, including 368 patients from Vietnam, Belgium, and Spain (168 from Europe and 200 from Asia), from November 2016 until June 2019. All patients underwent ovarian stimulation followed by oocyte retrieval in an antagonist protocol with a fixed daily dose of 150 IU rFSH until triggering. Blood sampling and DNA extraction was performed prior to oocyte retrieval, followed by genotyping of four SNPs from FSHR (rs6165, rs6166, rs1394205) and FSHB (rs10835638).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Eligible were predicted normal responder women <38 years old undergoing their first or second ovarian stimulation cycle. Laboratory staff and clinicians were blinded to the clinical results and genotyping, respectively. The prevalence of hypo-responders, the number of oocytes retrieved, the follicular output rate (FORT), and the follicle to oocyte index (FOI) were compared between different FSHR and FSHB SNPs genotypes.

MAIN RESULTS AND THE ROLE OF CHANCE

The prevalence of derived allele homozygous SNPs in the FSHR was rs6166 (genotype G/G) 15.8%, rs6165 (genotype G/G) 34.8%, and rs1394205 (genotype A/A) 14.1%, with significant differences between Caucasian and Asian women (P < 0.001). FSHB variant rs10835638 (c.-211 G>T) was very rare (0.5%). Genetic model analysis revealed that the presence of the G allele in FSHR variant rs6166 resulted in less oocytes retrieved when compared to the AA genotype (13.54 ± 0.46 vs 14.81 ± 0.61, estimated mean difference (EMD) -1.47 (95% CI -2.82 to -0.11)). In FSHR variant rs1394205, a significantly lower number of oocytes was retrieved in patients with an A allele when compared to G/G (13.33 ± 0.41 vs 15.06 ± 0.68, EMD -1.69 (95% CI -3.06 to -0.31)). A significantly higher prevalence of hypo-responders was found in patients with the genotype A/G for FSHR variant rs6166 (55.9%, n = 57) when compared to A/A (28.4%, n = 29), ORadj 1.87 (95% CI 1.08-3.24). No significant differences were found regarding the FORT across the genotypes for FSHR variants rs6166, rs6165, or rs1394205. Regarding the FOI, the presence of the G allele for FSHR variant rs6166 resulted in a lower FOI when compared to the A/A genotype, EMD -13.47 (95% CI -22.69 to -4.24). Regarding FSHR variant rs6165, a lower FOI was reported for genotype A/G (79.75 ± 3.35) when compared to genotype A/A (92.08 ± 6.23), EMD -13.81 (95% CI -25.41 to -2.21).

LIMITATIONS, REASONS FOR CAUTION

The study was performed in relatively young women with normal ovarian reserve to eliminate biases related to age-related fertility decline; thus, caution is needed when extrapolating results to older populations. In addition, no analysis was performed for FSHB variant rs10835638 due to the very low prevalence of the genotype T/T (n = 2).

WIDER IMPLICATIONS OF THE FINDINGS

Based on our results, genotyping FSHR SNPs rs6165, rs6166, rs1394205, and FSHB SNP rs10835638 prior to initiating an ovarian stimulation with rFSH in predicted normal responders should not be recommended, taking into account the minimal clinical impact of such information in this population. Future research may focus on other populations and other genes related to folliculogenesis or steroidogenesis.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by an unrestricted grant by Merck Sharp & Dohme (MSD). N.P.P. reports grants and/or personal fees from MSD, Merck Serono, Roche Diagnostics, Ferring International, Besins Healthcare, Gedeon Richter, Theramex, and Institut Biochimique SA (IBSA). N.L.V. and M.T.H. report consultancy and conference fees from Merck, Ferring, and MSD, outside the submitted work. P.D. has received honoraria for lecturing and/or research grants from MSD, Ferring International, and Merck. D.S. reports grants and/or personal fees from MSD, Ferring International, Merck Serono, Cook, and Gedeon Richter. A.R.N., B.A.M., C.S., J.M., L.H.L., P.Q.M.M., H.T., and S.G. report no conflict of interests.

TRIAL REGISTRATION NUMBER

NCT03007043.

Germline nuclear transfer in mice may rescue poor embryo development associated with advanced maternal age and early embryo arrest

STUDY QUESTION

Can pronuclear transfer (PNT) or maternal spindle transfer (ST) be applied to overcome poor embryo development associated with advanced maternal age or early embryo arrest in a mouse model?

SUMMARY ANSWER

Both PNT and ST may have the potential to restore embryonic developmental potential in a mouse model of reproductive ageing and embryonic developmental arrest.

WHAT IS KNOWN ALREADY

Germline nuclear transfer (NT) techniques, such as PNT and ST, are currently being applied in humans to prevent the transmission of mitochondrial diseases. Yet, there is also growing interest in the translational use of NT for treating infertility and improving IVF outcomes. Nevertheless, direct scientific evidence to support such applications is currently lacking. Moreover, it remains unclear which infertility indications may benefit from these novel assisted reproductive technologies.

STUDY DESIGN, SIZE, DURATION

We applied two mouse models to investigate the potential of germline NT for overcoming infertility. Firstly, we used a model of female reproductive ageing (B6D2F1 mice, n = 155), with ages ranging from 6 to 8 weeks (young), 56 (aged) to 70 weeks (very-aged), corresponding to a maternal age of <30, ∼36 and ∼45 years in humans, respectively. Secondly, we used NZB/OlaHsd female mice (7-14 weeks, n = 107), as a model of early embryo arrest. This mouse strain exhibits a high degree of two-cell block. Metaphase II (MII) oocytes and zygotes were retrieved following superovulation.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Ovarian reserve was assessed by histological analysis in the reproductive-aged mice. Mitochondrial membrane potential (△Ψm) was measured by JC-1 staining in MII oocytes, while spindle-chromosomal morphology was examined by confocal microscopy. Reciprocal ST and PNT were performed by transferring the meiotic spindle or pronuclei (PN) from unfertilised or fertilised oocytes (after ICSI) to enucleated oocytes or zygotes between aged or very-aged and young mice. Similarly, NT was also conducted between NZB/OlaHsd (embryo arrest) and B6D2F1 (non-arrest control) mice. Finally, the effect of cytoplasmic transfer (CT) was examined by injecting a small volume (∼5%) of cytoplasm from the oocytes/zygotes of young (B6D2F1) mice to the oocytes/zygotes of aged or very-aged mice or embryo-arrest mice. Overall, embryonic developmental rates of the reconstituted PNT (n = 572), ST (n = 633) and CT (n = 336) embryos were assessed to evaluate the efficiency of these techniques. Finally, chromosomal profiles of individual NT-generated blastocysts were evaluated using next generation sequencing.

MAIN RESULTS AND THE ROLE OF CHANCE

Compared to young mice, the ovarian reserve in aged and very-aged mice was severely diminished, reflected by a lower number of ovarian follicles and a reduced number of ovulated oocytes (P < 0.001). Furthermore, we reveal that the average △Ψm in both aged and very-aged mouse oocytes was significantly reduced compared to young mouse oocytes (P < 0.001). In contrast, the average △Ψm in ST-reconstructed oocytes (very-aged spindle and young cytoplast) was improved in comparison to very-aged mouse oocytes (P < 0.001). In addition, MII oocytes from aged and very-aged mice exhibited a higher rate of abnormalities in spindle assembly (P < 0.05), and significantly lower fertilisation (60.7% and 45.3%) and blastocyst formation rates (51.4% and 38.5%) following ICSI compared to young mouse oocytes (89.7% and 87.3%) (P < 0.001). Remarkably, PNT from zygotes obtained from aged or very-aged mice to young counterparts significantly improved blastocyst formation rates (74.6% and 69.2%, respectively) (P < 0.05). Similarly, both fertilisation and blastocyst rates were significantly increased after ST between aged and young mice followed by ICSI (P < 0.05). However, we observed no improvement in embryo development rates when performing ST from very-aged to young mouse oocytes following ICSI (P > 0.05). In the second series of experiments, we primarily confirmed that the majority (61.8%) of in vivo zygotes obtained from NZB/OlaHsd mice displayed two-cell block during in vitro culture, coinciding with a significantly reduced blastocyst formation rate compared to the B6D2F1 mice (13.5% vs. 90.7%; P < 0.001). Notably, following the transfer of PN from the embryo-arrest (NZB/OlaHsd) zygotes to enucleated non-arrest (B6D2F1) counterparts, most reconstructed zygotes developed beyond the two-cell stage, leading to a significantly increased blastocyst formation rate (89.7%) (P < 0.001). Similar findings were obtained after implementing ST between NZB/OlaHsd and B6D2F1 mice, followed by ICSI. Conversely, the use of CT did not improve embryo development in reproductive-age mice nor in the embryo-arrest mouse model (P > 0.05). Surprisingly, chromosomal analysis revealed that euploidy rates in PNT and ST blastocysts generated following the transfer of very-aged PN to young cytoplasts and very-aged spindles to young cytoplasts were comparable to ICSI controls (with young mouse oocytes). A high euploidy rate was also observed in the blastocysts obtained from either PNT or ST between young mice. Conversely, the transfer of young PN and young spindles into very-aged cytoplasts led to a higher rate of chromosomal abnormalities in both PNT and ST blastocysts.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

The limited number of blastocysts analysed warrants careful interpretation. Furthermore, our observations should be cautiously extrapolated to humans given the inherent differences between mice and women in regards to various biological processes, including centrosome inheritance. The findings suggest that ST or PNT procedures may be able to avoid aneuploidies generated during embryo development, but they are not likely to correct aneuploidies already present in some aged MII oocytes.

WIDER IMPLICATIONS OF THE FINDINGS

To our knowledge, this is the first study to evaluate the potential of PNT and ST in the context of advanced maternal age and embryonic developmental arrest in a mouse model. Our data suggest that PNT, and to a lesser extent ST, may represent a novel reproductive strategy to restore embryo development for these indications.

STUDY FUNDING/COMPETING INTEREST(S)

M.T. is supported by grants from the China Scholarship Council (CSC) (Grant no. 201506160059) and the Special Research Fund from Ghent University (Bijzonder Onderzoeksfonds, BOF) (Grant no. 01SC2916 and no. 01SC9518). This research is also supported by the FWO-Vlaanderen (Flemish fund for scientific research, Grant no. G051017N, G051516N and G1507816N). The authors declare no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Follicular-phase endometrial scratching: a truncated randomized controlled trial

STUDY QUESTION

Does intentional endometrial injury (scratching) during the follicular phase of ovarian stimulation (OS) increase the clinical pregnancy rate (CPR) in ART?

SUMMARY ANSWER

CPR did not vary between the endometrial injury and the control group, but the trial was underpowered due to early termination because of a higher clinical miscarriage rate observed in the endometrial injury arm after a prespecified interim analysis.

WHAT IS KNOWN ALREADY

Intentional endometrial injury has been put forward as an inexpensive clinical tool capable of enhancing endometrial receptivity. However, despite its widespread use, the benefit of endometrial scratching remains controversial, with several recent randomized controlled trials (RCTs) being unable to confirm its added value. So far, most research has focused on endometrial scratching during the luteal phase of the cycle preceding the one with embryo transfer (ET), while only a few studies investigated in-cycle injury during the follicular phase of OS. Also, the persistence of a scratch effect in subsequent treatment cycles remains unclear and possible harms have been insufficiently studied.

STUDY DESIGN, SIZE, DURATION

This RCT was performed in a tertiary hospital setting between 3 April 2014 and 8 October 2017. A total of 200 women (100 per study arm) undergoing IVF/ICSI in a GnRH antagonist suppressed cycle followed by fresh ET were included.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Participants were randomized with a 1:1 allocation ratio to either undergo a pipelle endometrial biopsy between Days 6 and 8 of OS or to be in the control group.The primary outcome was CPR. Secondary outcomes included biochemical pregnancy rate, live birth rate (LBR), early pregnancy loss (biochemical pregnancy losses and clinical miscarriages), excessive procedure pain/bleeding and cumulative reproductive outcomes within 6 months of the study cycle.

MAIN RESULTS AND THE ROLE OF CHANCE

The RCT was stopped prematurely by the trial team after the second prespecified interim analysis raised safety concerns, namely a higher clinical miscarriage rate in the intervention group. The intention-to-treat CPR was similar between the biopsy and the control arm (respectively, 44 versus 40%, P = 0.61, risk difference = 3.6 with 95% confidence interval = -10.1;17.3), as was the LBR (respectively, 32 versus 36%, P = 0.52). The incidence of a biochemical pregnancy loss was comparable between both groups (10% in the intervention group versus 15% in the control, P = 0.49), but clinical miscarriages occurred significantly more frequent in the biopsy group (25% versus 8%, P = 0.032). In the intervention group, 3% of the patients experienced excessive procedure pain and 5% bleeding. The cumulative LBR taking into account all conceptions (spontaneous or following ART) within 6 months of randomization was not significantly different between the biopsy and the control group (54% versus 60%, respectively, P = 0.43).

LIMITATIONS, REASONS FOR CAUTION

The trial was stopped prematurely due to safety concerns after the inclusion of 200 of the required 360 patients. Not reaching the predefined sample size implies that definite conclusions on the outcome parameters cannot be drawn. Furthermore, the pragmatic design of the study may have limited the detection of specific subgroups of women who may benefit from endometrial scratching.

WIDER IMPLICATIONS OF THE FINDINGS

Intentional endometrial injury during the follicular phase of OS warrants further attention in future research, as it may be harmful. These findings should be taken in consideration together with the growing evidence from other RCTs that scratching may not be beneficial.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by 'Fonds Wetenschappelijk Onderzoek' (FWO, Flanders, Belgium, 11M9415N, 1524417N). None of the authors have a conflict of interest to declare with regard to this study.

Stimulation of the ovaries in women with breast cancer undergoing fertility preservation: Alternative versus standard stimulation protocols; the study protocol of the STIM-trial

BACKGROUND

Chemotherapy for breast cancer may have a negative impact on reproductive function due to gonadotoxicity. Fertility preservation via banking of oocytes or embryos after ovarian stimulation with FSH can increase the likelihood of a future live birth. It has been hypothesized that elevated serum estrogen levels during ovarian stimulation may induce breast tumour growth. This has led to the use of alternative stimulation protocols with addition of tamoxifen or letrozole. The effectiveness of these stimulation protocols in terms of oocyte yield is unknown.

METHODS/DESIGN

Randomized open-label trial comparing ovarian stimulation plus tamoxifen and ovarian stimulation plus letrozole with standard ovarian stimulation in the course of fertility preservation. The study population consists of women with breast cancer who opt for banking of oocytes or embryos, aged 18-43years at randomisation. Primary outcome is the number of oocytes retrieved at follicle aspiration. Secondary outcomes are number of mature oocytes retrieved, number of oocytes or embryos banked and peak E2 levels during ovarian stimulation.

DISCUSSION

Concerning the lack of evidence on which stimulation protocol should be used in women with breast cancer and the growing demand for fertility preservation, there is an urgent need to undertake this study. By performing this study, we will be able to closely monitor the effects of various stimulation protocols in women with breast cancer and pave the way for long term follow up on the safety of this procedure in terms of breast cancer prognosis.

TRIAL REGISTRATION

NTR4108.

Open versus closed oocyte vitrification in an oocyte donation programme: a prospective randomized sibling oocyte study

STUDY QUESTION

Is the survival of donor oocytes with the CryotopSC device superior to the survival with the closed CBSvit device?

SUMMARY ANSWER

The CryotopSC device and the CBSvit device showed similar survival rates.

WHAT IS KNOWN ALREADY

Health authorities are cautious about possible cross contamination during liquid nitrogen storage or handling when working with open vitrification devices. At present, the use of open devices is still allowed since little information is available on the efficiency of closed devices.

STUDY DESIGN, SIZE, DURATION

A prospective randomized sibling oocyte study was performed in the Centre for Reproductive Medicine (UZBrussel) between January 2014 and July 2015. The survival after warming and the embryological outcome of donor oocytes vitrified using two devices was compared: the CBSvit device (closed vitrification and closed storage) and the CryotopSC device (open vitrification and closed storage). A difference of 10% was defined to prove the superiority of the CryotopSC device. In total, 250 warmed oocytes were needed in each arm.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Oocytes from 48 donors were included in the study: 253 vitrified with the CBSvit device and 257 with the CryotopSC device. Equal numbers of oocytes from both devices and originated from the same donor cycle were allocated to each of 78 recipients, in order to exclude donor and recipient (male factor) effects.

MAIN RESULTS AND THE ROLE OF CHANCE

There were no differences found between the CBSvit and the CryotopSC in terms of survival after warming (93.7 versus 89.9%) or fertilization per injected oocyte (74.3 versus 81.4%). The degeneration rate after ICSI was significantly higher for the CBSvit device: 11.4 versus 6.1% (P = 0.041). A significantly higher number of zygotes in the CryotopSC group finished their first mitosis 25-27 h post-injection (34.1 versus 52.1%, P = 0.001). On Day 3, the overall embryo quality distribution did not vary between groups, but a significantly higher cell number was obtained in the CryotopSC device: 6.8 ± 2.8 versus 7.6 ± 2.8 (P = 0.01). The utilization rate per mature oocyte, per surviving oocyte or per fertilized oocyte did not differ. The embryos with the highest quality were selected for transfer on Day 3. The clinical pregnancy rate per transfer cycle was 36.5%.

LIMITATIONS, REASONS FOR CAUTION

The results of this study should not be extrapolated to other female groups, since oocytes from young fertile donors were used in this study.

WIDER IMPLICATIONS OF THE FINDINGS

In many countries, the use of open devices is still allowed due to the limited reports on the efficiency of closed devices. Knowing the caution of health authorities about the use of open devices, there is an urgent need for efficiency studies with closed devices. The results obtained in the current study shows the efficiency of a safe closed vitrification device, leaving behind any concern about possible cross contamination during handling or storage.

STUDY FUNDING/COMPETING INTERESTS

No funding was obtained. The authors have no conflict of interest to declare.

TRIAL REGISTRATION NUMBER

NCT01952184.

TRIAL REGISTRATION DATE

24 September 2013.

DATE OF FIRST PATIENT'S ENROLMENT

23 January 2014.

Addition of highly purified HMG after corifollitropin alfa in antagonist-treated poor ovarian responders: a pilot study

STUDY QUESTION

Will sequential administration of highly purified (hp)-HMG after corifollitropin alfa in a GnRH antagonist protocol benefit women with poor ovarian response according to the Bologna criteria?

SUMMARY ANSWER

Corifollitropin alfa followed by hp-HMG in a GnRH antagonist protocol results in very promising pregnancy rates, albeit only in young (<40 years old) poor ovarian responders fulfilling the Bologna criteria.

WHAT IS KNOWN ALREADY

Poor ovarian responders fulfilling the Bologna criteria have a very poor prognosis in terms of successful IVF outcome. Although a recent study demonstrated low pregnancy rates in this group of patients after treatment with corifollitropin alfa followed by recombinant FSH in a GnRH antagonist protocol, previous studies showed that the addition of LH activity in 36- to 39-year-old women significantly increases implantation rates.

STUDY DESIGN, SIZE, DURATION

In this retrospective pilot study, we included poor ovarian responders fulfilling the Bologna criteria treated with a completely novel protocol, with corifollitropin alfa followed by hp-HMG in a GnRH antagonist setting. Overall, 51 patients were treated within a period of 1 year (August 2011-August 2012).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Patients received 150 μg corifollitropin alfa on second day of the menstrual cycle followed by a fixed daily dose of 0.25 mg of GnRH antagonist on Day 7 of the cycle onwards. On the ninth day of the cycle, a daily fixed dose of 300 IU hp-HMG was administered until the day of ovulation triggering. The primary outcome was ongoing pregnancy rate per patient.

MAIN RESULTS AND THE ROLE OF CHANCE

Among 47 eligible women, 29 patients were <40 years old and 18 patients were ≥ 40 years old. No differences were observed in endocrine profile, number of cycles with oocyte retrieval (66 versus 67%) and cycles with embryo transfer (62 versus 61%) in women <40 versus ≥ 40 years old, respectively. However, 8 of the 29 women <40 years old had an ongoing pregnancy (28%) compared with 0 of 18 patients who were ≥ 40 years of age (P = 0.017).

LIMITATIONS, REASONS FOR CAUTION

Owing to the specific retrospective study design, bias cannot be ruled out and these results should not be extrapolated to other treatment protocols for poor ovarian responders. Therefore, caution should be taken when interpreting the results.

WIDER IMPLICATIONS OF THE FINDINGS

The promising results from this pilot study of corifollitropin alfa followed by hp-HMG stimulation indicate a potential beneficial effect in young poor ovarian responders fulfilling the Bologna criteria. The data provide the rationale for performing a randomized controlled trial to determine if there is sound evidence for a clinical introduction of this protocol.

STUDY FUNDING/COMPETING INTEREST(S)

No conflicts of interest to declare. No specific funding was received for this study.

Survival and post-warming in vitro competence of human oocytes after high security closed system vitrification

PURPOSE

To compare two vitrification methods and two warming methods for human oocyte vitrification using a high security closed device in terms of survival, fertilization and embryo development.

METHODS

For vitrification, oocytes were (1) immediately placed in equilibration solution or (2) they were gradually exposed to the cryoprotectants. For warming, oocytes were placed (1) in a 25 μl preheated (37 °C) thawing solution droplet that was put at room temperature for 1 min once the oocytes were inside or (2) in a 150 μl droplet for 1 minute at 37 °C.

RESULTS

Survival and preimplantation development were significantly lower when warming was performed in a small preheated droplet. There was no significant difference in survival and embryo development between the gradual or direct exposure to cryoprotectants.

CONCLUSIONS

Using this high security closed vitrification device a 90 % survival rate can be achieved when the oocytes are immediately warmed in a large volume at 37 °C.

Live birth rates following natural cycle IVF in women with poor ovarian response according to the Bologna criteria

STUDY QUESTION

What is the effect of natural cycle IVF in women with poor ovarian response according to the new ESHRE definition for poor ovarian responders: the Bologna criteria?

SUMMARY ANSWER

Although natural cycle IVF is a promising treatment option for normal responders, poor ovarian responders, as described by the Bologna criteria, have a very poor prognosis and do not appear to experience substantial benefits with natural cycle IVF.

WHAT IS KNOWN ALREADY

Previous trials have shown that natural cycle IVF is an effective treatment for the general infertile population and might be an option for poor ovarian responders. However, none of the trials have examined the effect of natural cycle IVF in poor responders according to the Bologna criteria, the newly introduced definition by the ESHRE Working Group on Poor Ovarian Response Definition. In this trial, we examined the effect of natural cycle IVF in poor ovarian responders fulfilling the Bologna criteria.

STUDY DESIGN, SIZE, DURATION

In this retrospective cohort trial, 164 consecutive patients, undergoing 469 natural cycle IVFs between 2008 and 2011 were included. Patients were stratified as poor and normal responders: 136 (390 cycles) were poor ovarian responders according to the Bologna criteria, whereas 28 women (79 treatment cycles) did not fulfil the criteria and were considered as normal responders.

PARTICIPANTS/MATERIALS, SETTING, METHODS

All patients were monitored with hormonal analysis and ultrasound scan every second day, from Day 7 or 8 of the cycle onwards. When a follicle of >16 mm was observed, ovulation was triggered with 5000 IU of i.m. hCG and oocyte retrieval was performed 32 h later.

MAIN RESULTS AND THE ROLE OF CHANCE

Live birth rates in poor responders according to the Bologna criteria were significantly lower compared with the control group of women; the live birth rate per cycle was 2.6 versus 8.9%, P = 0.006 and the live birth rate per treated patient was 7.4 versus 25%, P = 0.005. In poor responders according to the Bologna criteria, live birth rates were consistently low and did not differ among different age groups (≤ 35 years, 36-39 years and ≥ 40 years), with a range from 6.8 to 7.9%.

LIMITATIONS, REASONS FOR CAUTION

A limitation of our analysis is its retrospective design; however, taking into account that we included only consecutive patients treated with exactly the same protocol, the likelihood of selection bias might be considerably limited. In addition, the control group in our study refers to women of younger age and therefore the promising results among patients who did not fulfil the Bologna criteria apply only to women of younger age.

WIDER IMPLICATIONS OF THE FINDINGS

Our trial suggests that although natural cycle IVF is a promising treatment option for younger normal responders, its potential is very limited to poor ovarian responders as described by the Bologna criteria, irrespective of patient's age. This highlights the very poor prognosis of these women and therefore the urgent need for future trials to examine the effect of ovarian stimulation protocols in women with poor ovarian response as described by the Bologna criteria.

STUDY FUNDING/COMPETING INTEREST(S)

No funding was used. There are no competing interests to declare.

Reproductive potential of a metaphase II oocyte retrieved after ovarian stimulation: an analysis of 23 354 ICSI cycles

BACKGROUND Live birth per cycle and live birth per embryo transfer are commonly used outcome measures for IVF treatment. In contrast, the assessment of the reproductive efficiency of human oocytes fertilized in vitro is seldom performed on an egg-to-egg basis. This approach may however gain importance owing to the increasingly widespread use of oocyte cryopreservation, as the technique is becoming more established. The aim of the current study is to quantify the reproductive efficiency of the oocyte according to ovarian ageing and ovarian response. METHODS We performed a retrospective analysis of the outcome of all consecutive patients attending for treatment between 1992 and 2009. The outcome in terms of live birth after fresh and cryopreserved embryo transfer per mature oocyte was calculated for 207 267 oocytes retrieved in 23 354 ovarian stimulation cycles. The oocyte utilization rate (number of live births per mature oocyte) was further analysed in relation to the ovarian response. RESULTS The oocyte utilization rate in women in the age of ≤ 37 years remains constant with a mean of 4.47% live birth per mature oocyte [95% confidence interval (CI): 4.32-4.61]. From the age of 38 years onwards, a significantly lower oocyte utilization rate was noted, declining from 3.80% at the age of 38 years to 0.78% at 43 years (P < 0.001). In this 38-43 years age group, oocyte utilization rate was no longer dependent on ovarian response (P = 0.87). CONCLUSIONS The major strength of the study, which is also its weakness, is the fact that we included a large number of cycles performed over a long period of time. According to our results, the oocyte utilization rate between 23 and 37 years of age depends largely on ovarian response and to a much lesser extent on age. From the age of 38 years onwards, the utilization rate depends largely on age and to a much lesser extent on ovarian response. Considering the increased use of oocyte freezing for fertility preservation, these data are extremely valuable as they provide an estimate of the number of oocytes needed to achieve a live birth.

From fresh heterologous oocyte donation to autologous oocyte banking

INTRODUCTION

Today, oocyte donation has become well established, giving rise to thousands of children born worldwide annually. The introduction of oocyte cryopreservation through vitrification allows the introduction of egg banking, improving the efficiency and comfort of oocyte donation. Moreover, the vitrification technique can now enable autologous donation of oocytes to prevent future infertility.

METHODS

We evaluated fresh heterologous oocyte donation in terms of obstetrical and perinatal outcome as well as of the reproductive outcome of past donors. We then evaluated the efficiency of a closed vitrification device and its clinical applications within ART. Thirdly, we evaluated the opinion of women with regard to preventive egg freezing and the efficiency of a human oocyte in relation to age.

RESULTS

Oocyte donation is associated with an increased risk of first trimester bleeding and pregnancy induced hypertension. Donating oocytes does not seem to increase the likelihood for a later need of fertility treatment. The chance of an oocyte to result in live birth (utilization rate) in women <37 years old remains constant with a mean of 4.47%. A significant proportion of young women would consider safeguarding their reproductive potential through egg freezing or are at least open to the idea.

DISCUSSION AND CONCLUSION

The introduction of efficient oocyte cryopreservation has revolutionized oocyte donation through the establishment of eggbank donation. The technique also enables women to perform autologous donation after preventive oocyte storage in order to circumvent their biological clock.

A survey on the intentions and attitudes towards oocyte cryopreservation for non-medical reasons among women of reproductive age

BACKGROUND

Although cryopreservation of semen is a routine procedure for preserving male gametes, an efficient method of preserving fertility through oocyte freezing has only recently become available for women. In view of the limited female reproductive lifespan, oocyte freezing can now offer women some protection against the decline in fertility with aging.

METHODS

A survey was performed in Belgium among 1914 women of reproductive age (21-40 years) to assess public attitudes towards the phenomenon called 'social oocyte freezing'. Women were questioned on their awareness of the age-related fertility decline and their views and intentions towards considering undergoing oocyte cryopreservation.

RESULTS

The electronic questionnaire was completed by 1049 women, giving a response rate of 55%, and 25 were excluded as they were incomplete/inconsistent. Our results demonstrate that 31.5% of respondents consider themselves as potential social oocyte freezers, of which 3.1% would definitely consider the procedure. Just over half of the women (51.8%) would not consider the procedure while 16.7% indicated they had no opinion. Potential oocyte freezers are characterized by a higher number of desired children and more openness to oocyte donation. The decision to actually embark on such treatment would primarily depend on conditions, such as the procedure not affecting their natural fertility and the health of future children.

CONCLUSIONS

We conclude that a significant proportion of young women would consider safeguarding their reproductive potential or are at least open to the idea of social oocyte freezing.