Evaluation of chromosomal abnormalities from preimplantation genetic testing to the reproductive outcomes: a comparison between three different structural rearrangements based on next-generation sequencing

Cytogenomic characterization of karyotypes with additional autosomal material

Chromosomal rearrangements involving additional material in individuals with phenotypic alterations usually result in partial trisomy, often accompanied by partial monosomy. To characterize chromosomal rearrangements and analyze genomic characteristics in the breakpoint regions in 31 patients with additional material on an autosomal chromosome. Different tests were performed to characterize these patients, including karyotyping, chromosomal microarray analysis (CMA), and fluorescent in situ hybridization (FISH). In silico analyses evaluated A/B chromosomal compartments, segmental duplications, and repetitive elements at breakpoints. The 31 rearrangements resulted in 47 copy number variations (CNVs) and a range of structural aberrations were identified, including six tandem duplications, 19 derivative chromosomes, two intrachromosomal rearrangements, one recombinant, two dicentric chromosomes, and one triplication. A deleted segment was associated with the duplication in 16 of the 19 patients with derivative chromosomes from translocation. Among the trios whose chromosome rearrangement origin could be investigated, 54,5% were de novo, 31,9% were maternally inherited, and 13,6% were paternally inherited from balanced translocations or inversion. Breakpoint analysis revealed that 22 were in the A compartment (euchromatin), 25 were in the B compartment (heterochromatin), and five were in an undefined compartment. Additionally, 14 patients had breakpoints in regions of segmental duplications and repeat elements. Our study found that a deletion accompanied by additional genetic material was present in 51.6% of the patients, uncovering the underlying genetic imbalances. Statistical analyses revealed a positive correlation between chromosome size and the occurrence of CNVs in the rearrangements. Furthermore, no preference was observed for breakpoints occurring in compartments A and B, repetitive elements, or segmental duplications.

ViLR: a novel virtual long read method for breakpoint identification and direct SNP haplotyping in de novo PGT-SR carriers without a proband

BACKGROUND

Despite the gradual application of third-generation long read sequencing (LRS) or reference embryo establishment to preimplantation genetic testing for structural rearrangement (PGT-SR) without familial involvement, there are still limitations to their extensive clinical application yet. This study developed a novel virtual NGS-based long read method (ViLR) and preliminarily evaluated its clinical feasibility of breakpoint characterization and direct SNP haplotyping for de novo chromosomal structural rearrangements (CSR).

METHODS

A total of 10 families with de novo CSR risk were enrolled in this study for ViLR analysis. In contrast to LRS, ViLR is a virtual long read solution that used the same barcoded labeling and assembly of different long gDNAs differently barcoded. Notably, ViLR could generate an average fragment length of over 30 Kb, with an N50 block size of up to 16 Mb in a single assay, allowing to achieve accurate breakpoint mapping and direct carrier's haplotyping. An approximately 2 Mbp region flanking upstream and downstream of each breakpoint was selected for informative SNP collection. Embryo haplotype determination was based on the established carriers' haplotypes after whole genome amplification and sequencing. To confirm PGT-SR results, we performed prenatal genetic diagnosis.

RESULTS

This study achieved an average mapping rate of 99.5%, > 90% coverage depth (> 10X), an average number of effective barcode (> 5 kb length) counts of 11,000,000 and an average fragment length of 40 kb, which generated sufficient informative SNPs for breakpoint characterization and haplotype phasing. ViLR analysis of 10 de novo PGT-SR carriers precisely identified breakpoints and haplotypes. Seven families obtained 18 euploid embryos, in which 10 were euploid/normal embryos, 7 were euploid/balanced carrier embryos, and the remaining one unknown was due to homologous recombination of the breakpoint region. Prenatal genetic diagnosis was performed for four women, and the outcomes coincided with the results from embryo PGT-SR. At the time of writing this paper, four healthy babies had been delivered uneventfully.

CONCLUSION

Here, we demonstrated the clinical potential of ViLR as a novel solution for breakpoint identification and direct SNP haplotyping in de novo PGT-SR families without proband involvement.

CLINICAL TRIAL NUMBER

Not applicable.

Derivative and non-derivative aneuploidy rates in PGT tested blastocysts from carriers of structural rearrangements

RESEARCH QUESTION

What is the likelihood of having an euploid embryo when undergoing preimplantation genetic testing for structural rearrangements (PGT-SR)?

DESIGN

PGT-SR data from 364 couples (2822 trophectoderm biopsies) with a reciprocal translocation (RecT, n = 263), Robertsonian translocation (RobT, n = 79) or inversion (Inv, n = 22) were analysed retrospectively. Rates of euploid, derivative aneuploid or non-derivative aneuploid were evaluated for each cycle, stratified by the type of rearrangement and parent of origin.

RESULTS

Inv had the highest rate of euploid embryos (47.0-52.5%), followed by RobT (34.1-45.2%) and RecT (24.0-28.2%). The rates of euploid embryos were significantly lower for carriers of RobT and RecT compared with age-matched controls (57.6-59.0%). Maternal versus paternal rearrangements had significantly higher rates of derivative-abnormal findings for RobT (41.6% versus 20.2%) and RecT (60.2% versus 52.7%). Aneuploidies involving other chromosomes did not differ significantly in frequency between rearrangement carriers (38.1-41.9%) and age-matched controls (40.6-42.4%).

CONCLUSIONS

Data from this study demonstrated that Inv carriers have the highest rates of euploid embryos among all carriers of chromosomal rearrangements, that maternal rearrangements confer a higher risk of abnormal embryos, and that evidence for an interchromosomal effect on aneuploidy rates was not present in this cohort. This analysis of over 2700 PGT-SR biopsies enabled generation of likelihood-of-transfer tables stratified by type of translocation, parent of origin, and number of biopsies, which can be used to help counsel patients pursuing PGT-SR.

ChromInst: a multicentre evaluation of robustness in aneuploidy and structural rearrangement testing

BACKGROUND

Preimplantation genetic testing for aneuploidy and for chromosomal structural rearrangement (PGT-A/-SR) can improve clinical pregnancy rates and live birth rates, and shorten the time to pregnancy. The large-scale statistics on their efficacy and accuracy across different centres, as well as the frequency of abnormalities for each chromosome, will provide a valuable supplement to previous research.

METHODS

Patients who had PGT-A or -SR procedures at five reproductive centres from 2018 to 2022 were recruited based on PGT-A/-SR indications. ChromInst and next-generation sequencing (NGS)-based PGT technology were utilised to detect copy number variations in embryos. Sequencing data metrics such as median absolute pairwise difference (MAPD) and detection success rate were analysed to evaluate the robustness of ChromInst. To assess ChromInst's accuracy, the chromosomal results from amniocentesis, abortions, and neonatal blood was as the gold standard for negative PGT results; the fluorescence in situ hybridisation (FISH), which was performed on embryos that identified as aneuploid through PGT was as the gold standard for positive PGT results. The frequency of abnormalities in each chromosome was also explored in aneuploid embryos.

RESULTS

A total of 5,730 embryos were tested from 1,015 patients in the study, 391 of whom had PGT-A and 624 of whom had PGT-SR. 99.5% (5,699/5,730) of the embryos had an NGS sequencing MAPD value < 0.25, and 99.3% (5,689/5,730) of the embryos achieved successful PGT-A/-SR detection. Compared with the gold standard, the concordance of negative PGT-A/-SR results was 99.8% (506/507), and that of positive results was 99.8% (1,123/1,125). The euploidy rate in the PGT-A population was 45.9% (981/2,135). The proportion of euploid + balanced embryos was highest among couples with non-polymorphic inversions (44.6%, 152/341), followed by those with Robertsonian translocations (39.0%, 293/752), and lowest among those with reciprocal translocations (22.5%, 483/2,143). Chromosomes 16, 22, and 15 had the highest frequency of autosomal trisomies among the embryos from PGT-A patients, while chromosomes 16, 22, and 21 had the highest frequency of monosomies. High-frequency chromosomes with de novo chromosomal abnormalities for trisomies and monosomies were similar in the PGT-SR patients to those in the PGT-A patients.

CONCLUSIONS

ChromInst-based PGT-A/-SR could accommodate operational variations among different clinical centres, ensuring accurate results through robust and stable detection performance. Prior to PGT-A/-SR, more trustworthy data could be provided to support the genetic counselling.

Factors affecting the reproductive outcome in reciprocal translocation carriers undergoing preimplantation genetic testing for structural rearrangements (PGTSR)

OBJECTIVE

To investigate the reproductive outcomes of balanced reciprocal translocation carriers and evaluate the association between the number of metaphase-II oocytes retrieved and cumulative live birth rates (LBRs).

METHODS

This retrospective analysis included 344 preimplantation genetic testing (PGT) for structural rearrangement cycles of 281 couples with balanced reciprocal translocations between January 2018 and January 2021. All patients included in the analysis had either delivered a baby or had used all their embryos after one stimulation cycle. All women were followed up for at least 2 years.

RESULTS

After ovarian stimulation and oocyte fertilization, 44.2% of PGT for structural rearrangements cycles achieved a live birth. Carrier's sex and female age did not affect the cumulative LBR of reciprocal translocation carriers. Cumulative LBRs steadily increased with the number of oocytes, reaching 64% when >20 oocytes were retrieved. The cutoff values for achieving at least one live birth were 9.5 metaphase-II (MII) oocytes and 3.5 biopsied embryos.

CONCLUSION

Couples with reciprocal translocations have lower transferable embryo rates and cumulative LBRs. The MII oocytes retrieved may be a crucial factor for cumulative LBRs. A high ovarian response may further increase cumulative LBRs, but avoidance of ovarian hyperstimulation syndrome or other iatrogenic complications should be considered.

Robust evidence reveals the reliable rate of normal/balanced embryos for identifying reciprocal translocation and Robertsonian translocation carriers

We aimed to evaluate the reliable rate of normal/balanced embryos for reciprocal translocation and Robertsonian translocation carriers and to provide convincing evidence for clinical staff to conduct genetic counselling regarding common structural rearrangements to alleviate patient anxiety. The characteristics of 39,459 embryos that were sourced from unpublished data and literature were analyzed. The samples consisted of 17,536 embryo karyotypes that were not published and 21,923 embryo karyotypes obtained from the literature. Using the PubMed, Cochrane Library, Web of Science, and Embase databases, specific keywords were used to screen the literature for reciprocal translocation and Robertsonian translocation. The ratio of normal/balanced embryos in the overall data was calculated and analyzed, and we grouped the results according to gender to confirm if there were gender differences. We also divided the data into the cleavage stage and blastocyst stage according to the biopsy period to verify if there was a difference in the ratio of normal/balanced embryos. By combining the unpublished data and data derived from the literature, the average rates of normal/balanced embryos for reciprocal translocation and Robertsonian translocation carriers were observed to be 26.96% (7953/29,495) and 41.59% (4144/9964), respectively. Reciprocal translocation and Robertson translocation exhibited higher rates in male carriers than they did in female carriers (49.60% vs. 37.44%; 29.84% vs. 27.67%). Additionally, the data for both translocations exhibited differences in the normal/balanced embryo ratios between the cleavage and blastocyst stages of carriers for both Robertsonian translocation and reciprocal translocation (36.07% vs 43.43%; 24.88% vs 27.67%). The differences between the two location types were statistically significant (P < 0.05). The normal/balanced ratio of embryos in carriers of reciprocal and RobT was higher than the theoretical ratio, and the values ranged from 26.96% to 41.59%. Moreover, the male carriers possessed a higher number of embryos that were normal or balanced. The ratio of normal/balanced embryos in the blastocyst stage was higher than that in the cleavage stage. The results of this study provide a reliable suggestion for future clinic genetic consulting regarding the rate of normal/balanced embryos of reciprocal translocation and Robertsonian translocation carriers.

Preimplantation genetic testing in couples with balanced chromosome rearrangement: a four-year period real world retrospective cohort study

BACKGROUND

Couples with balanced chromosome rearrangement (BCR) are at high risk of recurrent miscarriages or birth defects due to chromosomally abnormal embryos. This study aimed to provide real-world evidence of the euploidy rate of blastocysts from couples with BCR using preimplantation genetic testing (PGT) and to guide pretesting genetic counselling.

METHODS

A continuous four-year PGT data from couples with BCR were retrospectively analyzed. Biopsied trophectoderm cells were amplified using whole genome amplification, and next-generation sequencing was performed to detect the chromosomal numerical and segmental aberrations. Clinical data and molecular genetic testing results were analyzed and compared among the subgroups.

RESULTS

A total of 1571 PGT cycles with 5942 blastocysts were performed chromosomal numerical and segmental aberrations detection during the four years. Of them, 1034 PGT cycles with 4129 blastocysts for BCR couples were included; 68.96% (713/1034) PGT cycles had transferable euploid embryos. The total euploidy rate of blastocysts in couples carrying the BCR was 35.29% (1457/4129). Couples with complex BCR had euploid blastocyst rates similar to those of couples with non-complex BCR (46.15% vs. 35.18%, P > 0.05). Chromosome inversion had the highest chance of obtaining a euploid blastocyst (57.27%), followed by Robertsonian translocation (RobT) (46.06%), and the lowest in reciprocal translocation (RecT) (30.11%) (P < 0.05). Couples with males carrying RobT had higher rates of euploid embryo both in each PGT cycles and total blastocysts than female RobT carriers did, despite the female age in male RobT is significant older than those with female RobT (P < 0.05). The proportions of non-carrier embryos were 52.78% (95/180) and 47.06% (40/85) in euploid blastocysts from couples with RecT and RobT, respectively (P > 0.05). RecT had the highest proportion of blastocysts with translocated chromosome-associated abnormalities (74.23%, 1527/2057), followed by RobT (54.60%, 273/500) and inversion (30.85%, 29/94) (P < 0.05).

CONCLUSIONS

In couples carrying BCR, the total euploidy rate of blastocysts was 35.29%, with the highest in inversion, followed by RobT and RecT. Even in couples carrying complex BCR, the probability of having a transferable blastocyst was 46.15%. Among the euploid blastocysts, the non-carrier ratios in RecT and RobT were 52.78% and 47.06%, respectively. RecT had the highest proportion of blastocysts with translocated chromosome-associated abnormalities.

Preimplantation genetic testing using comprehensive genomic copy number analysis is beneficial for balanced translocation carriers

Balanced chromosomal translocation is one of chromosomal variations. Carriers of balanced chromosomal translocations have an increased risk of spontaneous miscarriage. To avoid the risk, preimplantation genetic testing (PGT) using comprehensive genomic copy number analysis has been developed. This study aimed to verify whether and how embryos from couples in which one partner is a balanced translocation carrier have a higher ratio of chromosomal abnormalities. A total of 894 biopsied trophectoderms (TEs) were obtained from 130 couples in which one partner was a balanced translocation carrier (Robertsonian translocation, reciprocal translocation, or intrachromosomal inversion) and grouped as PGT-SR. Conversely, 3269 TEs from 697 couples who experienced recurrent implantation failure or recurrent pregnancy loss were included in the PGT-A group. The transferable blastocyst ratio was significantly lower in the PGT-SR group, even when bias related to the sample number and patient age was corrected. Subgroup analysis of the PGT-SR group revealed that the transferable blastocyst ratio was higher in the Robertsonian translocation group. Because the PGT-SR group had a higher proportion of untransferable embryos than the PGT-A group, PGT using comprehensive genomic copy number analysis was more beneficial for balanced translocation carriers than for infertility patients without chromosomal translocations. The frequencies of de novo aneuploidies were further analyzed, and the frequency in the PGT-SR group was lower than that in the PGT-A group. Therefore, we could not confirm the existence of interchromosomal effects in this study.

Higher chromosomal abnormality rate in blastocysts from a subset of patients with pericentric inversion (Inv) 1 variant

The purpose of this study was to evaluate the incidence of unbalanced chromosome rearrangement in blastocyst-stage embryos from carriers of pericentric inversion of chromosome 1 (PEI-1). A total of 98 embryos from 22 PEI-1 carriers were tested for unbalanced rearrangements, originating from inversion carriers, and overall aneuploidy. Logistic regression analysis indicated that the ratio of inverted segment size to chromosome length was a statistically significant risk factor for unbalanced chromosome rearrangement from PEI-1 carriers (p = 0.003). The optimal cut-off values to predict the risk of unbalanced chromosome rearrangement was 36%, with the incidence being 2.0% in the <36% group and 32.7% in the ≥36% group. The unbalanced embryo rate was 24.4% in male carriers compared to 12.3% in female carriers. Inter-chromosomal effect analysis was performed using 98 blastocysts from PEI-1 carriers and 116 blastocysts from age-matched controls. PEI-1 carriers had similar sporadic aneuploidy rates compared to those of age-matched controls at 32.7 vs. 31.9%, respectively. In conclusion, the risk of unbalanced chromosome rearrangement is affected by inverted segment size in PEI-1 carriers.

Retrospective Analysis of Meiotic Segregation Pattern and Reproductive Outcomes in Blastocysts from Robertsonian Preimplantation Genetic Testing Cycles

In this retrospective study, 120 heterozygous Robertsonian translocation carriers undergoing preimplantation genetic testing (PGT) were included, between January 2018 and September 2021. Meiotic segregation patterns of 462 embryos from 51 female carriers and 69 male carriers were analyzed according to chromosome type, carrier's sex, and female age. The proportion of alternate embryos in female carriers was slightly lower than that in male carriers [P < 0.001, odds ratio (OR) = 0.512]. By contrast, no difference was observed among Rob (13;14), Rob (14;21), and rare RobT groups. Stratification analysis of female carriers' age doses showed no significant increase in unbalanced chromosomal abnormalities. Reproductive outcomes of 144 frozen-thawed cycles were analyzed. All 144 blastocysts were transferred, and there were no significant differences in the clinical pregnancy rates per transfer (CPR), miscarriage rates (MR), live birth rates per transfer (LBR), and cumulative live birth rates between female carriers and male carriers. In addition, couples in Rob (13;14), Rob (14;21), and rare RobTs groups had comparative clinical pregnancy rates per transfer (CPR), miscarriage rates (MR), live birth rates per transfer (LBR), and cumulative live birth rates. Our study demonstrated that the meiotic segregation pattern of Robertsonian translocations carriers is associated with the carrier's sex, but not the carrier's translocation type and female age. In addition, the sex of translocation carriers only affects the meiotic segregation pattern but does not influence the subsequent viability of normal embryos and live birth.

The composition dynamics of transposable elements in human blastocysts

Transposable elements (TEs) are mobile DNA sequences that can replicate themselves and play significant roles in embryo development and chromosomal structure remodeling. In this study, we investigated the variation of TEs in blastocysts with different parental genetic backgrounds. We analyzed the proportions of 1137 TEs subfamilies from six classes at the DNA level using Bowtie2 and PopoolationTE2 in 196 blastocysts with abnormal parental chromosomal diseases. Our findings revealed that the parental karyotype was the dominant factor influencing TEs frequencies. Out of the 1116 subfamilies, different frequencies were observed in blastocysts with varying parental karyotypes. The development stage of blastocysts was the second most crucial factor influencing TEs proportions. A total of 614 subfamilies exhibited different proportions at distinct blastocyst stages. Notably, subfamily members belonging to the Alu family showed a high proportion at stage 6, while those from the LINE class exhibited a high proportion at stage 3 and a low proportion at stage 6. Moreover, the proportions of some TEs subfamilies also varied depending on blastocyst karyotype, inner cell mass status, and outer trophectoderm status. We found that 48 subfamilies displayed different proportions between balanced and unbalanced blastocysts. Additionally, 19 subfamilies demonstrated varying proportions among different inner cell mass scores, and 43 subfamilies exhibited different proportions among outer trophectoderm scores. This study suggests that the composition of TEs subfamilies may be influenced by various factors and undergoes dynamic modulation during embryo development.

The aneuploidy testing of blastocysts developing from 0PN and 1PN zygotes in conventional IVF through TE-biopsy PGT-A and minimally invasive PGT-A

Zygotes without a pronuclear (0PN) or with one pronuclear (1PN) were defined as abnormal fertilization in conventional in vitro fertilization (IVF). The removal of 0PN and 1PN zygotes from conventional IVF cycles has always been controversial. This study aimed to investigate the chromosomal aneuploidy rates of 0PN- and 1PN-derived blastocysts in conventional IVF cycles and to assess the concordance rate between TE-biopsy PGT-A and miPGT-A. TE biopsies and culture media with blastocoel fluid (CM-BF) samples were whole-genome amplified by multiple annealing and looping-based amplification cycle-based single-cell ChromInst method. Next generation sequencing was performed for comprehensive chromosomal screening on a NextSeq550 sequencer using the NextSeq 500/550 High Output kit v2. The aneuploidy rates of 0PN-derived blastocysts were 19.7% for TE-biopsy PGT-A, and 36.1% for miPGT-A; the concordance rate for ploidy was 77.0%; and the sensitivity and specificity were 83.3% and 75.5%, respectively. The aneuploidy rates of 1PN-derived blastocysts were 37.5% and 37.5% by TE-biopsy PGT-A and miPGT-A, respectively; the concordance rate between TE biopsies and CM-BF samples was 83.3%; and the sensitivity and specificity were 77.8% and 86.7%, respectively. Regarding TE-biopsy PGT-A, there were no significant differences in aneuploidy rates among 0PN-, 1PN- and 2PN-derived blastocysts (PGT-M cycles) (19.7% vs. 37.5% vs. 24.3%, P = 0.226), but the aneuploidy rate of 1PN-derived blastocysts was slightly higher than the other two groups. An increase in aneuploidy rates was observed for 0PN/1PN-derived day 6 blastocysts compared to 0PN/1PN-derived day 5 blastocysts (TE-biopsy PGT-A: 35.7% vs. 19.3%, P = 0.099; miPGT-A: 39.3% vs. 35.1%, P = 0.705). The present study is the first that contributes to understanding the chromosomal aneuploidies in 0PN- and 1PN-derived blastocysts in conventional IVF cycles using TE-biopsy PGT-A and miPGT-A. The clinical application value of 0PN- and 1PN-derived blastocysts in conventional IVF should be assessed using TE-biopsy PGT-A or miPGT-A due to the existence of chromosomal aneuploidies.. In terms of consistency, the miPGT-A using blastocoel fluid enriched culture medium is promising as an alternative to TE-biopsy PGT-A for aneuploidy testing of 0PN- or 1PN-derived blastocysts in conventional IVF.

A Mini-Review Regarding the Clinical Outcomes of In Vitro Fertilization (IVF) Following Pre-Implantation Genetic Testing (PGT)-Next Generation Sequencing (NGS) Approach

Background: PGT-based NGS revolutionized the field of reproductive medicine, becoming an integrated component within current assisted reproductive technology (ART) protocols. Methods: We searched the literature published in the last half a decade in four databases (PubMed/Medline, ISI Web of Knowledge, ScienceDirect, and Scopus) between 2018 and 2022. Results: A total of 1388 articles were filtered, from which 60 met, initially, the eligibility criteria, but only 42 were included (≥100 patients/couples—62,465 patients and 6628 couples in total) in the present mini-review. In total, forty-two (70.0%) reported reproductive outcomes, while eighteen (30.0%) had distinct objectives. Furthermore, n = 1, 1.66% of the studies focused on PGT, n = 1, 1.66% on pre-implantation genetic testing for monogenic disorders (PGT-M), n = 3, 5.0% on pre-implantation genetic testing for structural rearrangements (PGT-SR) and n = 55, 91.66% on pre-implantation genetic testing for aneuploidies (PGT-A). Conclusions: PGT using NGS proved to be an excellent companion that folds within the current ascending tendency among couples that require specialty care. We strongly encourage future studies to provide a systematic overview expanded at a larger scale on the role of the PGT-NGS.

Implementation and Evaluation of Preimplantation Genetic Testing at Vilnius University Hospital Santaros Klinikos

Background and Objectives

The most effective treatment of infertility is in vitro fertilization (IVF). IVF with Preimplantation Genetic Testing (PGT) allows to identify embryos with a genetic abnormality associated with a specific medical disorder and to select the most optimal embryos for the transfer. PGT is divided into structural rearrangement testing (PGT-SR), monogenetic disorder testing (PGT-M), and aneuploidy testing (PGT-A). This study mostly analyzes PGT-SR, also describes a few cases of PGT-M. The aim of this study was to implement PGT procedure at Vilnius University Hospital Santaros Klinikos (VUHSK) Santaros Fertility Centre (SFC) and to perform retrospective analysis of PGT procedures after the implementation.

Materials and Methods

A single-center retrospective analysis was carried out. The study population included infertile couples who underwent PGT at SFC, VUHSK from January 01st, 2017 to December 31st, 2020. Ion PGM platform (Life Technologies, USA) and Ion ReproSeq PGS View Kit (Life Technologies, USA) were used for the whole genome amplification. Results were assessed using descriptive statistics.

Results

PGT was successfully implemented in VUHSK in 2017. During the analyzed time period, thirty-four PGT procedures were performed for 26 couples. Two procedures were performed in 2017, 7 procedures - in 2018, 13 - in 2019, and 12 - in 2020. In comparison with all IVF procedures, 2.5% procedures were IVF with PGT, a highest percentage was in 2020 (3.8% of all procedures). The main indication for PGT was balanced chromosomal rearrangements (in 85.3% cases). In all 34 cases 515 oocytes were aspirated in total, 309 oocytes were fertilized, oocytes fertilization rate exceeded 60%. A normal diploid karyotype was found in 46 (16.8%) biopsied embryos. Out of all PGT procedures, 9 (26.5%) resulted in a clinical pregnancy. Six (66.7%) pregnancies were confirmed in 2019, and 3 (33.3%) - in 2020. Three (33.3%) pregnancies resulted in spontaneous abortion, 6 (66.7%) - in delivery.

Conclusions

The implementation of PGT in VUHSK was successful. The most common indication for PGT was a reciprocal translocation. Oocytes fertilization rate exceeded 60%, a normal karyotype was found less than in one-fifth of biopsied embryos. A highest clinical pregnancy rate was achieved in 2019 when almost half of women conceived, which is probably related to the experience gained by the multidisciplinary team. This is the first study analyzing IVF with PGT in Lithuania, however, the results should be interpreted with caution due to a low number of total procedures performed.

Carrier screening and PGT for an autosomal recessive monogenic disorder: insights from virtual trials

PURPOSE

To assess the costs and benefits of carrier screening and preimplantation genetic testing (PGT) for recessive autosomal monogenic disorders for couples attempting assisted conception.

METHODS

A simulated first full cycle for women less than 35 years transferring embryos one at a time. The effect of testing on pregnancy outcomes was evaluated for different reporting scenarios. A Monte Carlo method utilising 1000 trials for 10,000 couples, testing 4, 16 and 38 genes, was used to assess the numbers likely to be at high risk and to estimate the incremental cost of screening and PGT to avoid an affected child.

RESULTS

PGT for high-risk couples: testing embryos only for the monogenic condition avoided 1 affected pregnancy for 4 cycles started. Combined with testing for chromosomal aneuploidy: ranking test results avoided 1 adverse pregnancy (affected, biochemical, clinical miscarriage) from 3 cycles started; 1 in 2 when excluding from transfer all embryos with an abnormal test result, within 1 in 25 fewer women achieving an unaffected live birth. Carrier screening for 4, 16 and 38 gene scenarios, where 1:250, 1:196 and 1:29 couples were at high risk: the incremental cost to prevent 1 affected live birth was estimated to be less than GBP 1,150,000 (US $1,587,000), < 836,642 (1,154,566) and < 137,794 (190,156), respectively, in 95% of trials.

CONCLUSIONS

Carrier screening combined with PGT, with and without testing for unrelated chromosomal abnormalities, for couples attempting assisted conception is complex but likely to be effective and also expensive.

Analysis of clinical outcomes and meiotic segregation modes following preimplantation genetic testing for structural rearrangements using aCGH/NGS in couples with balanced chromosome rearrangement

Purpose

To retrospectively evaluate the effectiveness of PGT-SR by array comparative genomic hybridization (aCGH) or next-generation sequencing (NGS) in preventing recurrent miscarriages.

Methods

Thirty one couples with balanced translocation who underwent 68 PGT-SR cycles between 2012 and 2020 were evaluated. A total of 242 blastocysts were biopsied for aCGH or NGS. The genetically transferable blastocysts were transferred in the subsequent frozen-thawed single embryo transfer cycle.

Results

The genetically transferable blastocyst rate was 21.2% (51/241). Thirty five genetically transferable blastocysts were transferred into the uterine cavity. The clinical pregnancy rate was 57.1% (20/35), and the ongoing pregnancy rate was 100.0% (20/20). The incidence of interchromosomal effect (ICE) was influenced by ovarian stimulation protocol, female age, and carrier's gender, but dependent on the types of balanced translocation carriers. Furthermore, there was no significant difference in meiotic segregation modes in ovarian stimulation protocols and carrier's gender. Interestingly, the incidence of adjacent-1 segregation in ≧40 years group increased significantly compared with <35 years group.

Conclusions

For the first time in Japan, we show the effectiveness of PGT-SR using aCGH or NGS, which enables comprehensive analysis of chromosomes, in the prevention of recurrent miscarriages. Furthermore, our results may support better genetic counseling of balanced translocation carriers for PGT-SR cycles.

The Relationship between Human Embryo Parameters and De Novo Chromosomal Abnormalities in Preimplantation Genetic Testing Cycles

DESIGN

In total, 456 PGT cycles, including 283 PGT-SR cycles and 173 PGT-A cycles, were assessed through comprehensive chromosome screening (CCS) from January 2017 to June 2020 at the Department of Reproductive Medicine of the Third Affiliated Hospital of Zhengzhou University. Trophectoderm (TE) biopsies were sequenced using next-generation sequencing (NGS). The incidence of de novo chromosome abnormalities was calculated, and the relationships between de novo chromosome abnormality rates and maternal age, number of oocytes retrieved, and parameters of cleavage-stage embryos and blastocyst-stage embryos were investigated.

RESULTS

The incidence of de novo chromosome abnormalities was 28.0% (318/1,135) in the PGT-SR cycles and 36.3% (214/590) in the PGT-A cycles, which increased with maternal age in both PGT-SR cycles (P = 0.018) and PGT-A cycles (P < 0.001). The incidence of de novo chromosome abnormalities was related to TE grade (P < 0.001), internal cell mass grade (P = 0.002), and development speed (day 5 vs. day 7: P < 0.001) of blastocyst-stage embryos. The incidence of de novo chromosomal abnormalities was irrelevant to the number of oocytes retrieved and the parameters of the embryo at the cleavage stage.

CONCLUSION

Blastocysts with higher morphology scores and faster progression had a lower incidence of de novo chromosome abnormalities, especially complex chromosome abnormalities. De novo chromosome abnormalities may negatively affect the morphological grading of blastocysts. Our findings will provide valuable information to the fertility doctor for embryo selection in non-PGT cycles.

PGT-SR (reciprocal translocation) using trophectoderm sampling and next-generation sequencing: insights from a virtual trial

PURPOSE

The objective of this virtual study was to simulate a full cycle and assess the costs and benefits to a couple with a reciprocal translocation, using current techniques for preimplantation genetic testing and comparing reporting every chromosome with only reporting those involved in the rearrangement.

METHODS

A simulation was constructed for women under the age of 35 years, where vitrified-warmed embryos were transferred one at a time in a first full cycle following preimplantation genetic testing using next-generation sequencing and sampling the trophectoderm at the blastocyst stage. The effect on pregnancy outcomes (live birth, clinical miscarriage and biochemical pregnancy) was evaluated for different reporting strategies for embryo transfer to (i) report only the rearranged chromosomes and transfer embryos with a normal or balanced test result for the translocation (targeted), or (ii) report every chromosome and exclude from transfer all embryos with an abnormal test result (exclusion), or (iii) exclude only those consistent with an unbalanced translocation and/or unrelated non-mosaic whole-chromosome aneuploidy and assign those with samples consistent with a normal or balanced translocation complement and unrelated mosaic aneuploidy or segmental imbalance (embryos of uncertain reproductive potential) a lower transfer priority (ranking). The number of individual women whom might benefit by avoiding an adverse pregnancy outcome (biochemical pregnancy, clinical miscarriage) or be disadvantaged by not achieving a live birth was evaluated. The financial cost of the different reporting strategies and the time taken to complete a cycle were also considered.

RESULTS

The simulation showed that compared to only reporting the translocation chromosomes (targeted reporting), testing every chromosome and ranking embryos by test result for transfer was a cost-effective strategy to avoid an adverse pregnancy without compromising the chance of a live birth. Excluding from transfer embryos with a test result consistent with a normal or balanced translocation complement of uncertain reproductive potential was an inferior strategy because it resulted in fewer live births from a full cycle. Reporting only the translocation chromosomes was an inferior strategy because it was less effective than ranked reporting of every chromosome to avoid an adverse pregnancy. Compared to targeted reporting, the ranked and exclusion strategies marginally reduced the overall cost and time taken to complete a full cycle. The ranking strategy avoided 1 adverse pregnancy for 12 cycles started, compared to 1 in 10 for the exclusion strategy which also resulted in 1 in 22 fewer women achieving a live birth. A minority (< 10%) of couples benefited by avoiding at least 1 adverse pregnancy whilst also reducing the time and cost for a complete cycle; most (> 70% ) couples received no benefit additional to targeted reporting and had the same outcome for pregnancy, time and cost.

CONCLUSIONS

The primary objective of PGT-SR for couples with a reciprocal translocation is to avoid a pregnancy with a chromosomally unbalanced product of the translocation and to reduce the risk of miscarriage, at least to that expected for couples with normal karyotypes. Trophectoderm sampling at the blastocyst stage with testing using NGS is an effective approach; however, ranking and excluding from transfer embryos with abnormal test results for unrelated chromosomes is problematical and is likely to be detrimental to achieving a live birth. Targeted reporting, where only the results of the chromosomes involved in the translocation are known, should be preferred to achieve a live birth. A best effort should be made to follow up and investigate all pregnancies following PGT-SR. Once the reproductive outcome is known (biochemical pregnancy, clinical pregnancy, live birth), the chromosomes unrelated to the rearrangement can be analysed as an experimental study. The risk/benefit of avoiding an adverse pregnancy vs reducing the chance of a healthy delivery should be a decision for each individual couple and informed by appropriate genetic counselling for their specific translocation and history.