P–566 Advanced paternal age can influence aneuploidy rate in egg donation cycles with poor sperm quality

Study question

Could advanced paternal age influences the embryos aneuploidy rate in eggs donation cycles with poor sperm quality?

Summary answer

In case of severe male factors increased paternal age can affect embryos aneuploidy rate in egg donation cycles.

What is known already

While the impact of advanced maternal age on reproductive is well understood, the effect of paternal age on reproductive function is controversial. Many studies have shown that Advanced Paternal Age (APA) could impact on male fertility potential affecting testicular function and sperm quality. Moreover, APA also has been associated with increased epigenetics changes and DNA mutations. Increased paternal age could be associated with different types of disorders such as autism, schizopherenia and bipolar disorders. Egg donation cycles, controlling female variables, represent the ideal model for the study of the impact of paternal age on reproductive outcomes.

Study design, size, duration

We retrospectively analyzed 43 egg donation cycles (October 2014-January 2020) with ≥ 50% survival rate of vitrified/warmed oocyte. Only cycles with poor sperm quality were considered. Cycles were divided in two GROUPS: group–1 included male paternal age ≤ 45 while group–2 included male paternal age >45. Data, shown as avarage±SD, were analyzed with Chi square or Student-t test.

Participants/materials, setting, methods

Group–1 included 20 cycles and 219 oocytes, male age was 40,89 ±6.12; Group–2 included 17 cycles and 173 oocytes, male age was 51±6.06. Respectively, in Group 1 and in Group 2, donor age were 22.4±2.65 and 24.8±3.88 (NS). All oocytes were injected with abnormal sperm samples according to WHO 2010. Embryos were cultured in time-lapse system until blastocyst stage. Trophectoderm biopsy and PGT-A analysis were performed according to standardized laboratory protocols.

Main results and the role of chance

Oocytes survival rates in Group1 and 2 were 86% (188/219) and 90.7% (157/173) (NS), respectively. Fertilization rates in Group1 and –2 were 71.42 (135/189) and 73.45% (119/162) (NS), respectively. The total number of obtained embryos (transferred + frozen) were 81 and 801 in Group–1 and –2, respectively. The rates of obtained embryos per reiceved occytes were 37% (81/219) and 46.24% (80/173) in Group–1 and –2 (p < 0.7), respectively. The PGT-A analysis showed 38.7% (31/80) and 31.17% (24/77) of euploid (NS) and 25% (20/80)and 42.85% (33/77) of aneuploid embryos (P < 0.05) in Group–1 and –2, respectively. Mosaic embryos were 33.5% (26/80) and 27.27%(21/77), in Group–1 and –2, respectively. (NS). These results indicate that in presence of severe male factor, advanced paternal age could increase embryos aneuploidy rate raising incidence of chromosomal abnormalities.

Limitations, reasons for caution

Each donor was stimulated with different protocols according to her history and hormones levels. Nothing is known about which type of sperm parameters (semen amount, morphology or motility) have a major impact when focusing on the embryos genetic outcome.

Wider implications of the findings: To better known the effect of APA, it could be necessary identify embryos chromosomal abnormalities and the correlation with specific sperm parameters. Further studies should be done to confirm the APA effect in patients with severe male factors and define a cut-off male age where PGT-A should be recommended.

Trial registration number

Not applicable

O-201 Prenatal and postnatal outcome of mosaic embryo transfers: multicentric study of one thousand mosaic embryos diagnosed by preimplantation genetic testing with trophectoderm biopsy

Study question

To explore the effect of chromosomal mosaicism detected in preimplantation genetic testing (PGT-A) on prenatal and postnatal outcome of mosaic embryo pregnancies

Summary answer

No significant difference between euploid and mosaic embryos was observed in terms of weeks of gestation, average weight, and developmental defect of the babies born

What is known already

Mosaic embryos have the potential to implant and develop into healthy babies. Transfer of these embryos is now offered as an option for women who undergo IVF resulting in no euploid embryos. While, prenatal diagnosis has shown the depletion of chromosomal mosaicism in mosaic embryos, several concerns remain. For instance, the direct effects of different kind of mosaicism on prenatal/postnatal outcome and the possibility that intra-biopsy mosaicism in the TE is a poor predictor of the ploidy status of the ICM. Thus, there is certainly a need for comprehensive analyses of obstetrical and neonatal outcome data of transferred mosaic embryos.

Study design, size, duration

Compiled analysis from multicenter data on transfers of mosaic embryos (n = 1,000) and their outcome, with comparison to a euploid control group (n = 5,561). To explore the effect of embryonic mosaicism on newborns, we matched mosaic embryos resulting in a birth with a euploid embryo by a series of parameters (maternal age, embryo morphology, and indication for PGT-A). Prenatal tests and birth characteristics of > 200 neonates from mosaic embryo transfers were compared to > 200 euploid embryos.

Participants/materials, setting, methods

PGT-A was performed on blastocyst-stage embryos with 24-Chromosome whole genome amplification (WGA)-based Next Generation Sequencing (NGS). In accordance with established guidelines, embryos were categorized as mosaic when PGT-A results indicated 20-80% aneuploid content. Prenatal testing where performed in 30% of pregnancies with amniocentesis, 4% did an extra analysis for potential UPD for the suspected mosaic chromosome, and an additional 16% performed chorionic villus sampling (CVS) and 9.5% performed noninvasive prenatal testing (NIPT).

Main results and the role of chance

Of the 465 mosaic embryos that implanted, about 20% miscarried, and out of those, 75% were early spontaneous abortions. Of the pregnancies, 3 out of 368 were stillborn (2 out of them were twins that were extremely premature at 23 weeks, and the other died during pregnancy from a heart defect). The remaining 99% of those have been born or are late ongoing pregnancies at the time of analysis. Prenatal tests were performed in > 200 pregnancies and the vast majority tested normal. All 5 abnormal cases were amniocentesis tests showing microdeletions or insertions of sizes smaller than the resolution used during PGT-A, so they were unrelated to the mosaicism detected with PGT-A. In fact, in none of the cases did the prenatal test reflect the mosaicism detected at the embryonic stage. Matching each of the 162 mosaic embryos resulting in a birth with a euploid embryo, we found that the length of gestation was similar on average, and so was the average weight of the babies at birth. We also gathered information on the routine physical examination performed on babies at birth, and of those 162 babies from mosaic embryo transfers, none had obvious developmental defects or gross abnormalities.

Limitations, reasons for caution

Even though newborns resulting from mosaic embryo transfers in this study invariably appeared healthy by routine examination, concerns for long-term health cannot yet be entirely dispelled. The question must therefore be carefully considered by each clinic and patient situation.

Wider implications of the findings

Prenatal testing of > 200 pregnancies from mosaic embryo transfers showed no incidence of mosaicism that matched the PGT-A findings, indicating the involvement of self-corrective mechanisms. Pregnancy and obstetric data indicates that mosaic embryos prevailing through gestation and birth have similar chromosomal and physiological health compared to euploid embryos.

Trial registration number

none

P–091 Magnetic Activated Cell Sorting (MACS) improves euploid blastocysts rate in pre-implantation genetic testing cycles with high levels of sperm DNA fragmentation and advanced paternal age

Study question

Can MACS increase euploid blastocyst rate in Pre-implantation Genetic Testing (PGT) cycles for AMA-APA (Advanced Maternal-Paternal Age) in patients with high sperm DNA fragmentation (SDF)?

Summary answer

A slight increase in euploid blastocyst rate was found using MACS in infertile patients with high SDF undergoing PGT cycles compared to the control group.

What is known already

Many authors have shown a close correlation between the presence of apoptotic markers on spermatozoa and the failure of assisted reproduction treatments. In normal physiological conditions, apoptotic spermatozoa with phosphatidylserine (PS) residues externalized on the plasma membrane, are eliminated along female genital tract, preventing oocyte fertilization. MACS eliminates apoptotic sperm whit PS residues using superparamagnetic microbeads conjugated with annexin V. This technique reduces the proportion of sperm with high rates of SDF and can be used to maximize ART procedures results. MACS application improves sperm quality, fertilization, cleavage and pregnancy rates reducing miscarriage rate.

Study design, size, duration

From June to November 2020, 10 couples in which MACS was applied to select non-apoptotic spermatozoa, were randomly enrolled in our study (MACS group) and 8 couples without MACS were considered as controls (No-MACS Group). All couples in both groups underwent a PGT cycle and had high sperm DNA Fragmentation (> 20%). A higher rate of euploid and diploid-euploid mosaic blastocysts were obtained in the MACS group compared to the control group.

Participants/materials, setting, methods

Patients with severe oligoastenoteratozoospermia were excluded. MACS protocol was performed as follows: semen sample was analyzed (WHO 2010) and washed with buffered medium; pellet was removed and a swim-up was performed. Retrieved spermatozoa were washed with a binding buffer (Miltenyi Biotec), centrifuged (400 g x 4 minutes) and supernatant discarded. Pellet was covered with Annexin-V and re-suspended. After 15 minutes incubation at room temperature, the sample was eluted through the column and collected for ICSI.

Main results and the role of chance

In MACS group, female and male mean age ± SD were 41.6 ± 2.1 and 43.5 ± 7.3, respectively. Female and male mean age ± SD were 41.7 ± 2.8 and 44.6 ± 8.1 in the No-MACS group, respectively. In MACS and No-MACS groups, injected oocytes were 44 and 35, fertilized oocytes were 32 (72.3%) and 27 (77.1%) (NS), blastocyst formation rates were 71.8% (23/32) and 48.1% (13/27) (NS), respectively. In No-MACS group, only 1 euploid and 1 diploid-euploid mosaic blastocysts were obtained (1/13 = 8%) (NS). In MACS group, 4 euploid blastocysts were formed (4/23 = 17.4%) whereas mosaic diploid-euploid blastocysts were 3/23 (13.0%) (NS). Aneuploid blastocysts were 16/23 (69.6%) in MACS group and 11/13 (84.6%) in No-MACS group (NS).

Limitations, reasons for caution

AMA and APA of couples enrolled should be considered as a limit of the study. A larger number of patients and biopsied blastocysts are needed to analyze clinical results and perform a robust statistical analysis establishing if MACS is useful to improve transferable blastocyst rate in patients with high SDF.

Wider implications of the findings: MACS is useful to select non apoptotic sperms; although fertilization, cleavage and blastocyst rates are not improved, aneuploid blastocysts rate slightly decreases using MACS. It I possible that, selecting spermatozoa free from PS residues, MACS allows to choose spermatozoa with a better DNA packaging, thus affecting the embryo ploidy.

Trial registration number

non applicable

"Universal Warming" protocol for vitrified oocytes to streamline cell exchange for transnational donation programs: a multi-center study

PURPOSE

To investigate the clinical efficacy of a "Universal Warming" protocol, based on subsequent steps with 1 M and 0.5 M concentration of extracellular cryoprotectant (ECCP), on shipped oocytes. Oocytes are vitrified using different brands of ready-to-use kits which recommend that the use of their own warming kit and combining different vitrification/warming kits may have legal consequences for assisted reproductive (AR) centers, until this practice has been validated with clinical studies.

METHODS

Retrospective multi-center transnational observational study. Number of oocytes warmed 1.898. Vitrification performed with vitrification kit (Kitazato, Japan); warming carried out randomly with two different kits: Kitazato warming kit and Vit Kit®-Thaw (FujiFilm Irvine, USA). Warmed oocytes were assigned to 2 groups: KK (Kitazato/Kitazato) 939, and KI (Kitazato/Irvine) 959. Primary endpoint: survival rate. Secondary endpoints: fertilization rate; blastulation rate; implantation rate; live birth rate.

RESULTS

Survival was comparable between the groups: 84.6% (795/939) in group KK vs 82.1% (787/959) in group KI. Fertilization rate was lower (P = 0.027) in group KK (75.7%-602/795) than in group KI (80.4%-633/787). Blastulation and implantation and live birth rates were all statistically comparable between the study groups: blastulation rate was 58.5% (352/602) vs 57.8% (366/633); implantation rate was 41.5% (80/193) vs 45.9% (84/183); live birth rate was 52.5% (62/118) in KK and 45.0% (54/120) in KI.

CONCLUSION

The use of this "Universal Warming" protocol simplifies vitrified oocyte exchange between AR centers in different countries, and overcomes potential regulatory/commercial/availability differences affecting clinical practice.

Comprehensive protocol of traceability during IVF: the result of a multicentre failure mode and effect analysis

STUDY QUESTION

Can traceability of gametes and embryos be ensured during IVF?

SUMMARY ANSWER

The use of a simple and comprehensive traceability system that includes the most susceptible phases during the IVF process minimizes the risk of mismatches.

WHAT IS KNOWN ALREADY

Mismatches in IVF are very rare but unfortunately possible with dramatic consequences for both patients and health care professionals. Traceability is thus a fundamental aspect of the treatment. A clear process of patient and cell identification involving witnessing protocols has to be in place in every unit. To identify potential failures in the traceability process and to develop strategies to mitigate the risk of mismatches, previously failure mode and effects analysis (FMEA) has been used effectively. The FMEA approach is however a subjective analysis, strictly related to specific protocols and thus the results are not always widely applicable. To reduce subjectivity and to obtain a widespread comprehensive protocol of traceability, a multicentre centrally coordinated FMEA was performed.

STUDY DESIGN, SIZE, DURATION

Seven representative Italian centres (three public and four private) were selected. The study had a duration of 21 months (from April 2015 to December 2016) and was centrally coordinated by a team of experts: a risk analysis specialist, an expert embryologist and a specialist in human factor. Principal investigators of each centre were first instructed about proactive risk assessment and FMEA methodology. A multidisciplinary team to perform the FMEA analysis was then formed in each centre. After mapping the traceability process, each team identified the possible causes of mistakes in their protocol. A risk priority number (RPN) for each identified potential failure mode was calculated. The results of the FMEA analyses were centrally investigated and consistent corrective measures suggested. The teams performed new FMEA analyses after the recommended implementations.

PARTICIPANTS/MATERIALS, SETTING, METHODS

In each centre, this study involved: the laboratory director, the Quality Control & Quality Assurance responsible, Embryologist(s), Gynaecologist(s), Nurse(s) and Administration. The FMEA analyses were performed according to the Joint Commission International.

MAIN RESULTS AND THE ROLE OF CHANCE

The FMEA teams identified seven main process phases: oocyte collection, sperm collection, gamete processing, insemination, embryo culture, embryo transfer and gamete/embryo cryopreservation. A mean of 19.3 (SD ± 5.8) associated process steps and 41.9 (SD ± 12.4) possible failure modes were recognized per centre. A RPN ≥15 was calculated in a mean of 6.4 steps (range 2-12, SD ± 3.60). A total of 293 failure modes were centrally analysed 45 of which were considered at medium/high risk. After consistent corrective measures implementation and re-evaluation, a significant reduction in the RPNs in all centres (RPN <15 for all steps) was observed. A simple and comprehensive traceability system was designed as the result of the seven FMEA analyses.

LIMITATIONS, REASONS FOR CAUTION

The validity of FMEA is in general questionable due to the subjectivity of the judgments. The design of this study has however minimized this risk by introducing external experts for the analysis of the FMEA results. Specific situations such as sperm/oocyte donation, import/export and pre-implantation genetic testing were not taken into consideration. Finally, this study is only limited to the analysis of failure modes that may lead to mismatches, other possible procedural mistakes are not accounted for.

WIDER IMPLICATIONS OF THE FINDINGS

Every single IVF centre should have a clear and reliable protocol for identification of patients and traceability of cells during manipulation. The results of this study can support IVF groups in better recognizing critical steps in their protocols, understanding identification and witnessing process, and in turn enhancing safety by introducing validated corrective measures.

STUDY FUNDING/COMPETING INTEREST(S)

This study was designed by the Italian Society of Embryology Reproduction and Research (SIERR) and funded by the Italian National Transplant Centre (CNT) of the Italian National Institute of Health (ISS). The authors have no conflicts of interest.

TRIAL REGISTRATION NUMBER

N/A.

Validation of a semiconductor next-generation sequencing-based protocol for preimplantation genetic diagnosis of reciprocal translocations

OBJECTIVE

We aim to validate a semiconductor next-generation sequencing (NGS)-based method to detect unbalanced chromosome translocation in preimplantation embryos.

METHODS

The study consisted of a blinded retrospective evaluation with NGS of 145 whole-genome amplification products obtained from biopsy of cleavage-stage embryos or blastocysts, derived from 33 couples carrying different balanced translocations. Consistency of NGS-based copy number assignments was evaluated and compared with the results obtained by array-comparative genomic hybridization.

RESULTS

Reliably identified with the NGS-based protocol were 162 segmental imbalances derived from 33 different chromosomal translocations, with the smallest detectable chromosomal segment being 5 Mb in size. Of the 145 embryos analysed, 20 (13.8%) were balanced, 43 (29.6%) were unbalanced, 53 (36.5%) were unbalanced and aneuploid, and 29 (20%) were balanced but aneuploid. NGS sensitivity for unbalanced/aneuploid chromosomal call (consistency of chromosome copy number assignment) was 99.75% (402/403), with a specificity of 100% (3077/3077). NGS specificity and sensitivity for unbalanced/aneuploid embryo call were 100%.

CONCLUSIONS

Next-generation sequencing can detect chromosome imbalances in embryos with the added benefit of simultaneous comprehensive aneuploidy screening. Given the high level of consistency with array-comparative genomic hybridization, NGS has been demonstrated to be a robust high-throughput technique ready for clinical application in preimplantation genetic diagnosis for chromosomal translocations, with potential advantages of automation, increased throughput and reduced cost.

Co-transfer of embryos derived from cryopreserved and fresh natural cycle oocytes: a pilot study

Italian legislation regarding reproductive medicine prohibits embryo storage while allowing cryopreservation of supernumerary oocytes. This study evaluated the effect of fresh oocytes obtained from natural unstimulated cycles on the clinical success rates derived from the use of frozen-thawed (FR-TH) oocytes obtained following ovarian stimulation. For 36 women, intracytoplasmic sperm injection was performed on FR-TH oocytes supplemented by a fresh oocyte, if available, derived from a natural cycle in which gonadotrophin-releasing hormone-antagonist was used for premature LH surge control. The retrieval rate of fresh oocytes was 61.1% and survival rate of FR-TH oocytes was 43.6%. The fertilization rate of fresh and FR-TH oocytes was 70% and 52.5%, respectively. Fifty embryos were transferred, 14 of them developed from fresh oocytes and 36 from FR-TH oocytes. Six pregnancies occurred in 10 cycles in which the embryos developed from fresh and FR-TH oocytes (pregnancy rate 60.0%) and two in 12 patients in whom the embryos were obtained from only FR-TH oocytes (pregnancy rate 16.7%) (P < 0.05). In summary, the data demonstrate that the transfer of embryos derived from oocytes cryopreserved following a previous ovarian stimulation and an embryo developed from a fresh one retrieved in natural cycle ensures an excellent clinical outcome.

Hopes and facts about mild ovarian stimulation

Over the last two decades, easier and less expensive stimulation treatments have been largely replaced by more complex and more demanding protocols. Since the mid-nineties, long-term gonadotrophin-releasing hormone agonist stimulation protocols have been widely used. Such lengthy expensive regimens are not free from short- and long-term risks and complications. Mild stimulation protocols reduce the mean number of days of stimulation, the total amount of gonadotrophins used and the mean number of oocytes retrieved. The proportion of high quality and euploid embryos seems to be higher compared with conventional stimulation protocols and the pregnancy rate per embryo transfer is comparable. Moreover, the reduced costs, the better tolerability for patients and the less time needed to complete an IVF cycle make mild approaches clinically and cost-effective over a given period of time. However, further prospective randomized studies are needed to compare cumulative pregnancy rates between the two protocols. Natural cycle IVF, with minimal stimulation, has been recently proposed as an alternative to conventional stimulation protocols in normo- and poor responder patients. Although acceptable results have been reported, further large prospective randomized studies are needed to better evaluate the efficacy of these minimal regimens compared with conventional stimulation approaches.

GnRH antagonists in ovarian stimulation for ICSI with oocyte restriction: a matched, controlled study

Italian legislation regarding reproductive medicine limits the number of embryos transferred per attempt to three. Thus, in order to achieve pregnancy, more IVF cycles may be required, generating a need for methods of ovarian stimulation with fewer side effects. The gonadotrophin-releasing hormone (GnRH) antagonists have several advantages in this respect, but there is a debate regarding a possible lower pregnancy rate from resulting cycles. This study evaluated the clinical applicability of GnRH antagonists for ovarian stimulation in young women undergoing intracytoplasmic sperm injection (ICSI) in which only three oocytes can be fertilized. The 200 women treated with GnRH antagonist had a significantly shorter stimulation and lower gonadotrophin consumption, oestradiol concentration, total and mature oocyte recovery as compared with 200 matched controls treated with GnRH agonist. No differences were found between the groups in the number of normal zygotes, total cleaved, transferred and high quality embryos, or in the clinical outcomes. Thus, the previously reported lower pregnancy rate in GnRH antagonist cycles may be related to the oocyte characteristics. Finally, under conditions of oocyte number restriction, the GnRH antagonist-based cycles may be proposed as an efficacious, safe and minimally invasive alternative to GnRH agonist in a standard long protocol.

Clinical application of laser-assisted ICSI: a pilot study

Human oocyte survival after intracytoplasmic sperm injection (ICSI) can be compromised by abnormal oolemma breakage patterns during the penetration of the microinjection needle. We previously reported a case of repeated ICSI failures associated with abnormal oolemma breakage in which a substantial improvement and successful pregnancy were achieved by performing ICSI through a laser-drilled hole in the zona pellucida (laser-assisted ICSI). This study was undertaken to compare the efficacy of laser-assisted ICSI with that of conventional ICSI in patients whose oocytes present this particular feature. Oocytes treated by laser-assisted ICSI (n=140) survived better (97.9% versus 85.7%; P<0.05) and tended to form more two-pronucleated zygotes (78.6% versus 69.2%; P=0.07) and less zygotes with three or more pronuclei (2.8% versus 7.8%; P=0.06) as compared with sibling oocytes treated by conventional ICSI (n=140). These data show that laser-assisted ICSI is suitable for oocytes with propensity for sudden oolemma breakage during conventional ICSI. The reduction of oocyte damage with laser-assisted ICSI as compared to conventional ICSI may be useful in other clinical indications where only few oocytes are available or when the oocyte survival after ICSI can be supposed to be compromised.

Cumulative pregnancy rates after transfer of fresh and thawed embryos

Frozen-thawed embryo transfer is an effective procedure that allows further possibilities of pregnancy in addition to those obtained after the fresh in vitro fertilization (IVF). In our follow-up study we analysed all fresh embryo transfer procedures and every frozen-thawed embryo transfer performed from January 2000 to December 2001 evaluating the cumulative pregnancy rates. The study population was divided into two groups according to the female age: <38 years (group I) and >38 years (group II). All the best embryos were chosen for transfer and all the supernumerary good quality embryos were cryopreserved on the day of transfer. The embryos were then thawed and manipulated using a new technique. In group I, 527 patients (619 cycles) underwent fresh embryo transfer and in 232 of them (238 cycles) the embryos were frozen (44% per patients and 38.4% per cycle). In group II, 156 patients (193 cycles) underwent fresh embryo transfer and in 14 of them (15 cycles) the embryos were frozen (9% per patient and 7.8% per cycle). The pregnancy rate of group I patients that had their supernumerary embryos frozen (232 patients and 238 cycles) was 47.4% per cycle and 48.7% per patient whereas in the same population of group II patients (14 patients and 15 cycles) the clinical pregnancy rate was 35.7% per cycle and 38.5% per patients. The cumulative clinical pregnancy rate after transfer of fresh and thawed embryos was: group I, 74% per cycle and 76% per patients; group II, 42.8% per cycle and 46.1% per patient. Frozen-thawed embryo transfer is a cost-effective practice.

Implantation in patients over 40 and raising FSH levels--a review

There is an evident decline of female fertility with age. This decline is mainly due to increased risk of pregnancy termination either after conception or after embryo implantation. Very likely the major cause of this embryo and pregnancy loss is chromosomal aneuploidies caused mostly by increasing rates of 'poor quality' oocytes. This phenomenon can be explained either by an age dependent accumulation of damage and/or by the hypothesis that the defective oocytes are there in the ovaries from the fetal life. 'Good quality' oocytes are ovulated first, leaving 'poor quality' oocytes to be ovulated later in life. Besides the quality of the oocytes which is mainly responsible of the embryo quality (we have not to forget a paternal effect) the process of implantation is dependent upon two variables: the probability of a viable embryo and that of a receptive uterine environment. From the oocyte donation model it seems that the endometrium also plays a minor role in human reproductive ageing as it does in some laboratory animals. However, besides some macroscopic possible causes which may play a role in the reduction of the age-related endometrial receptivity, there are so many endometrial factors possibly related to its receptivity which need to be further studied especially in older women.

Polscope analysis of meiotic spindle changes in living metaphase II human oocytes during the freezing and thawing procedures

BACKGROUND

The clinical efficacy of the current methods used for cryopreservation of metaphase II human oocytes is low. Meiotic spindle disorders are thought to be largely responsible for this situation.

METHODS

Supernumerary fresh metaphase II human oocytes were cryopreserved in 1,2-propanediol with 0.1 M sucrose using a slow freezing/rapid thawing programme. Meiotic spindles were analysed in these living metaphase II oocytes at sequential steps of the freezing and thawing procedures with the use of a computer-assisted polarization microscopy system (Polscope).

RESULTS

The meiotic spindle was detected in all 56 oocytes (from 16 patients) before freezing and remained visible in all these oocytes throughout the preparation for freezing up to the time that they were loaded into cryopreservation straws. Immediately after thawing, the spindle was visible in 35.7% of oocytes, but it disappeared in all of the thawed oocytes during the subsequent washing steps. However, the spindle reappeared in all surviving thawed oocytes after washing (57.4%), by 3 h of incubation at 37 degrees C in culture medium.

CONCLUSIONS

The current techniques of oocyte freezing and thawing inevitably cause meiotic spindle destruction. All spindles observed in thawed oocytes result from post-thaw reconstruction.

Relationship between meiotic spindle location with regard to the polar body position and oocyte developmental potential after ICSI

BACKGROUND

The recent development of a computer-assisted polarization microscopy system (Polscope) with which the meiotic spindle can be visualized in living oocytes on the basis of its birefringence permits analysis of the meiotic spindles of oocytes subjected to ICSI. Previous studies have shown that the meiotic spindle is not always aligned with the first polar body (PB) in metaphase II human oocytes prepared for ICSI. In the present study, the relationship between the degree of meiotic spindle deviation from the first PB location and ICSI outcome was analysed.

METHODS

Oocytes were divided into four groups according to the angle of meiotic spindle deviation from the PB position. The angle of deviation was 0-5 degrees, 6-45 degrees, 46-90 degrees and >90 degrees for groups I to IV respectively.

RESULTS

The rates of normal [2 pronuclei (PN)] and abnormal (1PN or >2PN) fertilization did not differ between groups I, II and III. However, the rate of normal fertilization was lower among oocytes in which the meiotic spindle deviation angle was >90 degrees; this led to an increased proportion of tripronucleated zygotes that failed to extrude the second PB. When embryos developed from normally fertilized oocytes were evaluated on day 3 after ICSI, no relationship was found between the angle of meiotic spindle deviation and embryo quality. The meiotic spindle was not detected in only 9% of oocytes, and these showed a higher incidence of fertilization and cleavage abnormalities than did oocytes in which the spindle was detected. When oocytes at metaphase I after cumulus oophorus and corona radiata removal were matured in vitro, the meiotic spindle was detected in 53.8% of those that reached metaphase II. In these in-vitro-matured oocytes the meiotic spindle was always aligned with the first PB, suggesting that misalignment seen in those oocytes matured in vivo resulted from PB displacement during manipulations for cumulus and corona removal.

CONCLUSION

High degrees of misalignment between the meiotic spindle and the first PB predict an increased risk of fertilization abnormalities. However, when normal fertilization had occurred, the cleavage potential of embryos developing from such oocytes was not impaired. These findings facilitate the selection of oocytes for ICSI in situations when the creation of supernumerary embryos is to be avoided.

Skeletal myogenic potential of human and mouse neural stem cells

Distinct cell lineages established early in development are usually maintained throughout adulthood. Thus, adult stem cells have been thought to generate differentiated cells specific to the tissue in which they reside. This view has been challenged; for example, neural stem cells can generate cells that normally originate from a different germ layer. Here we show that acutely isolated and clonally derived neural stem cells from mice and humans could produce skeletal myotubes in vitro and in vivo, the latter following transplantation into adult animals. Myogenic conversion in vitro required direct exposure to myoblasts, and was blocked if neural cells were clustered. Thus, a community effect between neural cells may override such myogenic induction. We conclude that neural stem cells, which generate neurons, glia and blood cells, can also produce skeletal muscle cells, and can undergo various patterns of differentiation depending on exposure to appropriate epigenetic signals in mature tissues.