Preimplantation Genetic Testing For Structural Rearrangements Research Articles

Total gonadotropin dose did not affect euploid blastocyst rates: an analysis of more than 19,000 oocytes.

To evaluate whether increasing total gonadotropin (Gn) dose is associated with changes in euploid blastocyst rate in preimplantation genetic testing (PGT) oocytes. This retrospective cohort study was conducted between 2017 and 2022, and 19,246 oocytes were grouped and analyzed based on tri-sectional quantiles of total Gn doses. Single reproductive medical center. All the patients who underwent PGT cycles, including PGT for aneuploidy, monogenic disorders, and structural rearrangements, were included. Next-generation sequencing platforms for chromosomal analysis. Blastocyst formation and euploid blastocyst rates. In total, 19,246 oocytes and 5375 PGT blastocysts were analyzed. There were significant differences in blastocyst formation and euploid blastocyst rates among the groups classified according to tri-sectional quantiles of total Gn doses. Significant differences in age, body mass index (BMI), proportion of primary infertility, anti-Müllerian hormone (AMH) levels, number of oocytes retrieved, controlled ovarian stimulation (COS) regimen, type of Gn, and PGT category were observed among the three groups. After stratifying the analysis by age, BMI, infertility diagnosis, AMH levels, number of oocytes retrieved, PGT category, type of Gn, and COS regimen, significant differences were only seen in a small number of specific subgroups. Furthermore, the results of the multiple logistic regression analysis showed that the blastocyst formation and euploid blastocyst rates did not significantly increase or decrease with the total Gn dose, whether treated as a continuous variable or divided into three Gn groups as categorical variables. Notably, advancing age was a risk factor for blastocyst formation and euploid blastocyst rates. PGT for structural rearrangements was a risk factor for blastocyst formation and euploid blastocyst rates as compared with PGT for aneuploidy. In the total PGT cycles, advancing age, and preimplantation genetic testing for structural rearrangements negatively affected blastocyst formation and euploid blastocyst rates; however, the total Gn dose did not affect blastocyst formation and euploid blastocyst rates.

P-249 Morphokinetic parameters comparison between balanced and unbalanced embryos from patients with structural chromosome abnormalities

Abstract Study question Are there morphokinetic differences between balanced and unbalanced embryos after PGT-SR? Summary answer The total time embryos remain at the morula stage (TiCAV- TM) could be a morphokinetic marker to consider in PGT-SR cycles. What is known already Due to the preimplantation genetic testing for structural rearrangements (PGT-SR) it is possible to identify embryos with an excess or defect of genetic material associated with a parental structural rearrangement. This technique is suitable for patients with a normal phenotype but a balanced chromosomal rearrangement. These patients have a higher risk of spontaneous abortion, as well as higher aneuploidy rates. Within structural chromosomal alterations, translocations are the most common presentation of chromosomal rearrangement. Study design, size, duration Within this multicentre retrospective study, we evaluated 133 embryos, from 39 cycles in which one of the partners had a karyotype with balanced reciprocal or Robertsonian translocations, from January 2021 to September 2023. After PGT-SR was carried out, we obtained 40 balanced embryos and 93 unbalanced embryos. Participants/materials, setting, methods We compared the conventional morphokinetic parameters and the duration of each state between two groups after PGT-SR samples were analysed. All embryos were cultured in Geri® time-lapse incubators, and underwent embryo biopsy on day 5-7. Statistical analysis was conducted using R software (v.4.3.1), including the following confounding variables: origin of karyotype alteration (maternal or paternal), type of translocation (Robertsonian or reciprocal), female and male gamete age, type of oocyte (fresh or frozen) and oocyte origin. Main results and the role of chance We observed that the mean age of the oocyte was significantly higher in the unbalanced embryos compared to the balanced ones (32.85±5.32 years vs.30.45±5.01 years). In terms of the altered karyotype, the paternal origin is more prevalent than the maternal one (60.9% vs. 39.1%). Regarding the type of translocation, reciprocal translocation is more predominant than Robertsonian translocation (83.5% vs. 16.5%) in our study population. When comparing morphokinetic parameters between both groups, we observed that unbalanced embryos tend to reach an expanded blastocyst stage later than balanced embryos (107.62±10.02h vs. 102.48±8.87h, respectively; p = 0.008, corrected p-value=0.186). We observed the same tendency with hatching initiation time (110.64±10.49h vs. 105.91±9.38h; p = 0.013, corrected p-value=0.296). We observed that unbalanced embryos have a slower development than balanced embryos (TiCAV-TFB 10.10±4.46h vs. 8.35±3.79h; p = 0.006, corrected p-value=0.437; TiH-TiCAV 13.03±5.98h vs. 11.79±5.50h; p = 0.017, corrected p-value=0.816). We did observe significant differences in total time at morula stage (TiCAV – TM) when comparing unbalanced and balanced embryos (12.60±6.94 vs. 8.88±5.65; p = 0.003, corrected p-value=0.001). Limitations, reasons for caution A higher number of embryos should be evaluated in order to enhance the statistical power of this study, as there is an important difference in sample size between balanced and unbalanced embryos in the PGT-SR cycles included in this study. Wider implications of the findings Further morphokinetic study of embryos from patients with structural chromosomal abnormalities can open up new lines of research and can help us to predict the final outcome of the cycle, accompanied by a genetic study. Trial registration number Not applicable

P-534 Toward enhanced genetic counseling with PGT-SR: exploring the impact of chromosomal rearrangement type and carrier gender on the acquisition of transferable embryos

Abstract Study question Do chromosomal rearrangement type and gender of carriers influence the ability to obtain transferable embryos? Summary answer Carriers of a reciprocal translocation, particularly female carriers, could have a higher risk of having non-transferable embryos. What is known already Chromosomal translocations are common structural rearrangements in the general population, occurring even 10 times more frequently in the infertile population, as carriers may produce unbalanced chromosomal gametes. Preimplantation Genetic Testing for Structural Rearrangements (PGT-SR) is a crucial tool for selecting embryos to transfer. There are numerous factors that can affect the availability of transferable embryos, and some of the less studied ones are the gender of the carrier and the type of chromosomal rearrangement. Study design, size, duration This is a single-center retrospective study performed between 2016 and 2023, that included 265 biopsies. Embryos were classified as transferable (n = 80, 30%) if they were euploid/balanced or exhibited low-grade mosaicism (< 50%) without the involvement of chromosomes 13, 14, 16, 18, 21, and X. Non-transferable embryos (n = 185, 70%) included those that were unbalanced, aneuploid, or displayed high-grade mosaicism. Differences between groups were assessed using Chi-square and Fisher’s exact tests. Values with p < 0.05* were deemed significant. Participants/materials, setting, methods NGS-based PGT-SR was performed on 265 embryos from 71 cycles of 47 couples. Couples were divided into Robertsonian translocation carrier group (ROB-T, 105 embryos) and Reciprocal translocation carrier group (REC-T, 160 embryos). Subsequently, data was categorized by maternal age: ≤37 (ROB-T=91, REC-T=122) and >37 years (ROB-T=14, REC-T=38), as well as by the gender of the carrier: male carrier group (MC) (ROB-T=77, REC-T=97) and female carrier group (FC) (ROB-T=29, REC-T=74). Main results and the role of chance Of the embryos belonging to ROB-T group, 45/105 (43%) were transferable, while in the REC-T group only 35/160 (22%) were transferable. This difference was statistically significant (p = 0.0004612). It was assessed whether these differences were attributable to maternal age or gender of carriers. In the ≤37, 43% (39/91) of the ROB-T embryos were transferable, but only 25% (30/122) were transferable in the REC-T group (p = 0.007583). In the >37, 43% (6/14) of the ROB-T embryos were transferable versus 13% (5/38) in the REC-T group (p = 0.04951). In both age groups, the obtaining transferable embryos were influenced by the type of translocation. In the MC group, 47% (36/76) of the ROB-T embryos were transferable and only 24% (22/90) were transferable in the REC-T group (p = 0.003467). In the FC group, 31% (9/29) of the ROB-T embryos and 19% (13/70) of the REC-T embryos were transferable (p = 0.2749). In the MC group, the obtaining transferable embryos were influenced by the type of translocation. However, within the FC group, no significant differences were observed. When evaluating non-transferable embryos (185), 71% were unbalanced and 29% were balanced ones with aneuploidies. Unbalanced embryos were more frequent in REC-T carriers in all analyzed groups. Limitations, reasons for caution This study is limited by its retrospective nature and its small sample size. Additionally, it is worth noting the difference in sample size between groups when segmenting the data by maternal age. Wider implications of the findings Our results indicate that the type of rearrangement is relevant in obtaining transferable embryos. Carriers of REC-T, especially female carriers, could have a higher risk of having non-transferable embryos compared to carriers of ROB-T. These findings could be significant for genetic counseling of individuals carrying chromosomal translocations. Trial registration number Not applicable

Which factors affect the live birth outcome of the first single euploid frozen-thawed blastocyst transfer in couples with balanced chromosomal translocations?

The objective of this study is to investigate the factors that influence the live birth rate (LBR) of the first single euploid frozen-thawed blastocyst transfer (FBT) cycles after preimplantation genetic testing for structural rearrangements (PGT-SR) in couples with balanced chromosomal translocations (BCT). Single center, retrospective and observational study. A total of 336 PGT-SR and the first single euploid FBT cycles between July 2016 and December 2022 were included in this study. The patients were divided into two groups according to the live birth outcomes. The parameters of the study population, controlled ovarian stimulation cycles, and FBT cycles were analyzed. Multivariable binary logistic regression was performed to find the factors that affected the LBR. The percentage of blastocysts at developmental stage Day 5 compared to Day 6 (51.8% vs. 30.8%; P<0.001) and with morphology ≥BB compared to <BB (49.7% vs. 32.2%; P=0.001) was significantly different between the group that resulted in live births (n=193) and the group that did not (n=143). The results of the multivariable binary logistic regression analysis indicated that the developmental stage (adjusted OR: 2.068, 95%CI 1.291-3.313; P=0.003) and morphology (adjusted OR: 1.697, 95%CI 1.039-2.773; P=0.035) of the blastocyst were significantly correlated with live birth. Patients with blastocysts that reached the developmental stage at Day 5 and had a morphology of ≥BB had a higher likelihood of having a live birth. The developmental stage and morphology of blastocyst affect the live birth outcome of the first single euploid FBT in BCT carriers undergoing PGT-SR.

The effect of carrier characteristics and female age on preimplantation genetic testing results of blastocysts from Robertsonian translocation carriers.

To analyze factors affecting segregation and ploidy results from Robertsonian carriers, and determine chromosomes involved impact chromosome stability during meiosis and mitosis. This retrospective study include 928 oocyte retrieval cycles from 763 couples with Robertsonian translocations undergoing preimplantation genetic testing for structural rearrangements (PGT-SR) using next-generation sequencing (NGS) between December 2012 and June 2020.The segregation patterns of the trivalent of 3423 blastocysts were analyzed according to the carrier's sex and age. A total of 1492 couples who received preimplantation genetic testing for aneuploidy (PGT-A) were included as the control group and matched according to maternal age and testing time stage. A total of 1728 (50.5%) normal/balanced embryos were identified from 3423 embryos diagnosed. The rate of alternate segregation in male Robertsonian translocation carriers was significantly higher than that in female carriers (82.3% vs. 60.0%, P < 0.001). However, the segregation ratio exhibited no difference between young and older carriers. Further, increasing maternal age decreased the proportion of transferable embryo cycle in both female and male carriers. And the ratio of chromosome mosaic from the Robertsonian translocation carrier group was significantly higher than that in the PGT-A control group (1.2% vs. 0.5%, P < 0.01). The meiotic segregation modes were affected by the carrier sex and were independent of the carrier's age. Advanced maternal age decreased the probability of obtaining a normal/balanced embryo. In additional, the Robertsonian translocation chromosome could increase the possibility of chromosome mosaicism during mitosis in blastocysts.

PGT-SR: A Comprehensive Overview and a Requiem for the Interchromosomal Effect

Preimplantation genetic testing for structural rearrangements (PGT-SR) was one of the first applications of PGT, with initial cases being worked up in the Delhanty lab. It is the least well-known of the various forms of PGT but nonetheless provides effective treatment for many carrier couples. Structural chromosomal rearrangements (SRs) lead to infertility, repeated implantation failure, pregnancy loss, and congenitally affected children, despite the balanced parent carrier having no obvious phenotype. A high risk of generating chromosomally unbalanced gametes and embryos is the rationale for PGT-SR, aiming to select for those that are chromosomally normal, or at least balanced like the carrier parent. PGT-SR largely uses the same technology as PGT-A, i.e., initially FISH, superseded by array CGH, SNP arrays, Karyomapping, and, most recently, next-generation sequencing (NGS). Trophectoderm biopsy is now the most widely used sampling approach of all PGT variants, though there are prospects for non-invasive methods. In PGT-SR, the most significant limiting factor is the availability of normal or balanced embryo(s) for transfer. Factors directly affecting this are rearrangement type, chromosomes involved, and sex of the carrier parent. De novo aneuploidy, especially for older mothers, is a common limiting factor. PGT-SR studies provide a wealth of information, much of which can be useful to genetic counselors and the patients they treat. It is applicable in the fundamental study of basic chromosomal biology, in particular the purported existence of an interchromosomal effect (ICE). An ICE means essentially that the existence of one chromosomal defect (e.g., brought about by malsegregation of translocation chromosomes) can perpetuate the existence of others (e.g., de novo aneuploidy). Recent large cohort studies of PGT-SR patients seem, however, to have laid this notion to rest, at least for human embryonic development. Unless new evidence comes to light, this comprehensive review should serve as a requiem.

Do chromosomal inversion carriers really need preimplantation genetic testing?

This study aimed to evaluate the rates of euploidy, aneuploidy, and mosaicism in preimplantation genetic testing for structural rearrangements (PGT-SR) cycles from chromosomal inversion carriers. In addition, this work also focused on assessing the impact of some contributors on the incidence of parental originating aneuploidy and mosaicism. This retrospective review enrolled chromosomal inversion carrier couples of whom the females were under 38years old undergoing PGT-SR at a single academic reproductive center. Subgroups were divided according to the gender of carriers, the inversion type, and the semen parameters of male carriers (male factor infertility (MF) or non-MF). Patient demographics, cycle characteristics, and PGT-SR outcomes were compared among subgroups. A total of 71 PGT-SR cycles from 57 inversion carrier couples were included for analysis. Among the 283 blastocysts, 48.4% were identified as euploidy, 27.9% as aneuploidy, and the remaining 23.7% as mosaicism. Only 32.9% of aneuploid embryos and 1.5% of mosaic embryos involved the parental inversion chromosomes. Notably, the female inversion carriers seemed to produce more parental originating aneuploid embryos than male inversion carriers (45.5% vs 23.9%, p = 0.044). The type of inversion and sperm parameters of male chromosomal inversion carriers did not affect the ploidy status of embryos. The incidence of parental originating aneuploidy in inversion carrier couples is lower than expected. For male chromosomal inversion carriers with normal sperm condition whose female partners are under 38years old, natural conception combined with prenatal diagnosis could be provided as an option during fertility counseling.

UNBALANCED TRANSLOCATION RATES IN PREIMPLANTATION EMBRYOS FROM COUPLES WITH COMPLEX CHROMOSOMAL REARRANGEMENT

Complex chromosomal rearrangements (CCRs) are constitutional structural rearrangements that involve three or more chromosomes with more than two breakpoints. CCR carriers have a high risk of recurrent spontaneous abortion and birth of offspring with abnormal phenotype. The Preimplantation genetic testing for structural rearrangement (PGT-SR) can reduce the miscarriage rate and improve clinical outcomes. However, the odds of normal or balanced embryo for CCR carriers is very low. There are scanty data on the effect of different types of CCR on abnormal embryo rate.

Influence of gender of reciprocal translocation carriers on the occurrence of embryonic chromosomal abnormalities

To explore the influence of gender of chromosomal translocation carriers on the occurrence of embryonic chromosomal aberrations. A retrospective study was carried out. Data were collected from 235 couples carrying reciprocal translocations (1163 blastocysts) and 70 couples carrying Robertsonian translocations (351 blastocysts). The preimplantation genetic testing for structural rearrangement (PGT-SR) analysis of 1514 blastocysts were completed through next generation sequencing (NGS). After adjusting the confounding factors such as female age, AMH, ovarian stimulation regimen, and Gn dosage, the results showed that the risk for blastocyst chromosomal abnormalities was 0.41 [OR(95%CI), 1.41(1.06, 1.87), P < 0.05] times higher in female reciprocal translocation carriers and 1.02 [OR(95%CI), 2.02 (1.20, 3.40), P < 0.01] times higher in female Robertsonian translocation carriers compared with male carriers, respectively. Compared with male carriers, the risk of blastocyst chromosomal abnormalities was increased by 0.67 times [OR(95%CI), 1.67 (1.10, 2.56), P < 0.05] in female reciprocal translocation carriers over 30 years old and 1.06 times [OR(95%CI), 2.06 (1.02, 4.15), P = 0.0434, P < 0.05] in female Robertsonian translocation carriers between 25 and 30 years old. Compared with male carriers, female carriers of reciprocal or Robertsonian translocations have a higher risk for producing embryos with chromosomal abnormalities, and their age may also be a risk factor.

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.

Are ovarian responses and the number of transferable embryos different in females and partners of male balanced translocation carriers?

To compare ovarian response and the number of transferable embryos between women with balanced autosomal translocations and women whose partners carry the translocation (control group). To investigate the predictive value of metaphase II (MII) oocyte number and biopsied embryo number for gaining at lowest one transferable embryo. We retrospectively analyzed 1942 preimplantation genetic testing for structural rearrangements (PGT-SR) cycles of 1505 balanced autosomal translocation couples over 8years. All cycles were divided into two subgroups: Robertsonian and reciprocal translocations (ROBT and ReBT). Receiver operator characteristic (ROC) curves were plotted to ascertain a cutoff of MII oocytes and biopsied embryos as predictors of gaining at lowest one transferable embryo. There were no statistical differences in baseline features or ovarian response indicators regarding the number of retrieved/MII oocytes, E2 level on the day of HCG, and ovarian sensitivity index (OSI) between women with balanced autosomal translocations and control group (P > 0.05). A decreased number of transferable embryos were found in women with balanced autosomal translocations regardless of the type of translocation. The cutoff values for gaining at lowest one transferable embryo are 12.5 MII oocytes and 4.5 biopsied embryos, respectively. Women with balanced autosomal translocations have a normal ovarian response, but fewer transferable embryos, meaning that higher gonadotropin (Gn) doses may be required to increase transferable embryos. When fewer than 12.5 MII oocytes or 4.5 blastocysts are obtained in a PGT-SR cycle, couples should be notified that the likelihood of gaining a transferable embryo is low.

Second biopsy for embryos with inconclusive results after preimplantation genetic testing: Impact on pregnancy outcomes

In this study, we aimed to evaluate the pregnancy outcomes for embryos biopsied twice at cleavage and blastocyst stage for preimplantation genetic testing (PGT). This retrospective monocentric study, conducted between January 2016 and March 2021, described all PGT results on one hand and the PGT results for undiagnosed embryos submitted to a second biopsy on the other hand. Among the 5865 embryos biopsied during the study period, 510 embryos were genetic undiagnosed after the first embryo biopsy at cleavage stage (8.7%). The rate of undiagnosed embryos was significantly higher for PGT for structural rearrangement (PGT-SR) than PGT for monogenic disease (PGT-M) (10.2% vs 7.4% respectively, p < 0.001). Thirty-three embryos were compatible with a second biopsy at blastocyst stage before being directly frozen. Among them 17 were diagnosed as healthy for the researched pathology (51.5%). At the time of our study, 11 of the 17 preserved embryos were thawed and transferred. Embryo survival at thawing was 100% and 5 pregnancies were obtained (clinical pregnancy rate of 45.5% per transfer), including 3 live births. A second biopsy for inconclusive embryos after PGT does not seem to have an impact on thaw survival and implantation rate. For couple, this strategy avoids to discard transferable embryos.

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

Abstract 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 &amp;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 &amp;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

Preimplantation genetic testing for structural rearrangement based on low-coverage next-generation sequencing accurately discriminates between normal and carrier embryos for patients with translocations

Research questionCan preimplantation genetic testing for structural rearrangement (PGT-SR) based on low-coverage next-generation sequencing (NGS) accurately discriminate between normal and carrier embryos of reciprocal translocation (RecT) and Robertsonian translocation (RobT)? DesignA total of 109 couples with RecT or RobT were included in this study. The ages, bad obsteric histories (BOH), blood karyotype and IVF cycle information, including the number of cumulus–oocyte complexes, metaphase II oocytes, two pronuclei oocytes and blastocysts were recorded. 0.1 × whole genome sequencing (WGS) of embryos followed by copy number variation (identifying unbalanced/balanced) and 2 × WGS of parents and embryos followed by haplotype analysis (discriminating between normal and carrier) were carried out in PGT-SR cycles. The embryos without translocation were transferred and clinical outcomes evaluated. ResultsAmong all the couples in this study, 67 patients had RecT and 42 had RobT. After unbalanced and balanced detection, 103 balanced embryos underwent a further normal and carrier discrimination procedure, and 53 normal embryos were identified. Finally, 32 normal embryos were transferred, with an ongoing pregnancy rate of 46.88% (15/32). All ongoing pregnancies underwent amniocentesis, and the amninocentesis karyotyping results showed 100% concordance with PGT-SR diagnosis. ConclusionsOur low-coverage NGS-based PGT-SR method can accurately discriminate between normal and carrier status of balanced embryos. The method is cost-effective and has broad clinical applicability.

EP472: Deriving risk estimates for balanced rearrangement carriers utilizing PGT-SR data

Parental balanced rearrangements (PBRs) are identified in approximately 4% of couples with recurrent pregnancy loss compared to 0.2% in the general population. PBR carriers are typically healthy, as little or no chromosomal material is lost or gained; however, they are at increased risk of creating unbalanced embryos that can result either in miscarriage or in the birth of a child with health problems and/or birth defects. Currently, most couples carrying PBRs are counseled based on risk estimates from either gamete studies (sperm/ova) or rates of miscarriage and/or abnormal live births. Preimplantation genetic testing for structural rearrangements (PGT-SR) can be performed for many types of PBRs, with detection dependent on the specific chromosome breakpoints and the testing technology used. Using data from PGT-SR cycles can generate risk estimates that are more informative for the IVF community regarding success rates for PBR couples. Trophectoderm biopsies were analyzed using a modified FAST-SeqS NGS-based PGT method and bioinformatics pipeline, which detects whole chromosome and segmental aneuploidies (≥10Mb), most types of polyploidy, and many instances of single chromosome uniparental isodisomy. A retrospective analysis of all embryo biopsies from patients with an identified PBR from September 2015 to March 2021 was performed to analyze rates of abnormalities derived from the PBR [derivative chromosomes and whole-chromosome aneuploidy of the involved chromosome(s)]. A total of 238 patients, with 380 PGT-SR cycles, were analyzed. The largest cohort, carrying reciprocal translocations, included 172 patients with 280 cycles (50.6% maternal, 49.4% paternal). The observed rates of derivative abnormalities were similar between the two groups (58.51% maternal vs. 50.41% paternal). Robertsonian translocations were documented in 50 patients with 81 cycles (48.0% maternal, 52.0% paternal). Unlike reciprocal translocations, we observed a clear increase in derivative abnormalities from maternally-derived rearrangements (36.4% vs. 18.2%), with the most striking difference seen with rob(14;21) carriers (n=9; 36.4% maternal vs. 3.1% paternal). Finally, sixteen patients (19 cycles) carried inversions, with eleven pericentric and five paracentric inversions represented. Similar to Robertsonian translocations, we observed an increase in derivative abnormalities when the pericentric inversion was maternally-derived (34.4% vs. 17.7%). Unexpectedly, a single paternally-derived paracentric inversion, inv(3)(q26.1q29), produced 37.5% blastocyst-stage derivative-abnormal embryos. Overall, as expected from the literature, derivative-abnormal rates from PBRs are highest for reciprocal translocation carriers, followed by Robertsonian translocations and inversions. While gamete studies have shown a higher rate of abnormalities in maternally-derived translocations, our abnormal rates were similar between the two parent-of-origin groups. In contrast, there is a clear parent-of-origin effect for both Robertsonian translocations and inversions. In all PBR types, abnormal rates are lower than those observed in gametes, likely due to decreased viability of abnormal embryos even before the blastocyst stage. These rates, derived from the largest published cohort to date, can be a valuable tool in counseling patients with PBRs regarding the potential success of their IVF journey.

Identifying Balanced Chromosomal Translocations in Human Embryos by Oxford Nanopore Sequencing and Breakpoints Region Analysis.

Background: Balanced chromosomal aberrations, especially balanced translocations, can cause infertility, recurrent miscarriage or having chromosomally defective offspring. Preimplantation genetic testing for structural rearrangement (PGT-SR) has been widely implemented to improve the clinical outcomes by selecting euploid embryos for transfer, whereas embryos with balanced translocation karyotype were difficult to be distinguished by routine genetic techniques from those with a normal karyotype. Method: In this present study, we developed a clinically applicable method for reciprocal translocation carriers to reduce the risk of pregnancy loss. In the preclinical phase, we identified reciprocal translocation breakpoints in blood of translocation carriers by long-read Oxford Nanopore sequencing, followed by junction-spanning polymerase chain reaction (PCR) and Sanger sequencing. In the clinical phase of embryo diagnosis, aneuploidies and unbalanced translocations were screened by comprehensive chromosomal screening (CCS) with single nucleotide polymorphism (SNP) microarray, carrier embryos were diagnosed by junction-spanning PCR and family haplotype linkage analysis of the breakpoints region. Amniocentesis and cytogenetic analysis of fetuses in the second trimester were performed after embryo transfer to conform the results diagnosed by the presented method. Results: All the accurate reciprocal translocation breakpoints were effectively identified by Nanopore sequencing and confirmed by Sanger sequencing. Twelve embryos were biopsied and detected, the results of junction-spanning PCR and haplotype linkage analysis were consistent. In total, 12 biopsied blastocysts diagnosed to be euploid, in which 6 were aneuploid or unbalanced, three blastocysts were identified to be balanced translocation carriers and three to be normal karyotypes. Two euploid embryos were subsequently transferred back to patients and late prenatal karyotype analysis of amniotic fluid cells was performed. The outcomes diagnosed by the current approach were totally consistent with the fetal karyotypes. Conclusions: In summary, these investigations in our study illustrated that chromosomal reciprocal translocations in embryos can be accurately diagnosed. Long-read Nanopore sequencing and breakpoint analysis contributes to precisely evaluate the genetic risk of disrupted genes, and provides a way of selecting embryos with normal karyotype, especially for couples those without a reference.

Complex reciprocal translocations, more complex than initially thought: a case report

ObjectiveTo present a case of a couple who experienced spontaneous abortion after the transfer of a preimplantation genetic testing for structural rearrangement (PGT-SR) normal/balanced embryo. The embryo was later determined to have significant paternally inherited chromosome deletion that was not previously identified as part of a complex translocation.DesignCase report.SettingSingle infertility practice.Patient(s)A 35-year-old patient with a history of five spontaneous abortions and her 36-years-old partner, a carrier of a balanced reciprocal translocation.Intervention(s)In vitro fertilization with PGT-SR and follow-up genetic testing.Main Outcome Measure(s)Identification of a paternal reciprocal translocation, pregnancy outcome after PGT-SR, and follow-up genetic testing after the spontaneous abortion of a PGT-SR normal/balanced embryo.Result(s)Karyotyping for a couple with a history of recurrent pregnancy loss identified a paternal reciprocal translocation between chromosomes 5 and 17 after G-banding analysis. In vitro fertilization with PGT-SR resulted in one normal/balanced embryo. The couple experienced a 9-week spontaneous abortion of the transfer of the embryo. Testing of product of conception identified a 3.2-Mb deletion on chromosome 17 resulting in the loss of 55 known genes and deemed likely pathogenic. Repeat karyotyping using G-banding and metaphase fluorescence in situ hybridization identified an additional chromosomal translocation, a segment of chromosome 17 translocated to chromosome 6, the same segment of deoxyribonucleic acid absent from the fetus.Conclusion(s)Preimplantation genetic testing for structural rearrangement cases are complex. Genetic testing must be completed with the best available technology by a reliable testing center. We, therefore, recommend that all chromosomal translocations detected by G-banding be further investigated with metaphase fluorescence in situ hybridization. When unexpected results occur in this patient population, testing beyond the standard of care may be required, including advanced molecular testing.

P–552 Delayed blastocyst development is associated with a higher risk of aneuploidy in patients of advanced maternal age

Abstract Study question Is delayed blastocyst development, assessed by the day of trophectoderm (TE) biopsy, associated with higher rates of aneuploidy? Summary answer Our findings show an association between delayed blastocyst development and poorer prognosis, in terms of euploidy rates, in patients of advanced maternal age. What is known already Extended culture of embryos past day 5 of development has become routine practice in all freeze-all cycles, including those applying preimplantation genetic testing for aneuploidies (PGT-A). As healthy live births have been obtained from day 6 and day 7 blastocysts, increasing the pool of embryos available for PGT-A is beneficial, particularly for patients of advanced maternal age who face higher cancellation rates. Nevertheless, the association between delayed blastocyst development and aneuploidy rates remains unclear. As current studies have reported opposing findings, detailed analysis of the chromosomal constitution of slowly developing embryos remains paramount. Study design, size, duration Retrospective, international, multicentre cohort study of 4211 patients undergoing preimplantation genetic testing for aneuploidy (PGT-A) from January 2016 to July 2020. We evaluated the chromosomal status of 14757 blastocysts tested using TE biopsy and next generation sequencing (NGS). Both autologous and donation cycles were included in the analysis. Cycles were excluded if they utilised preimplantation genetic testing for monogenic disorders (PGT-M) or preimplantation genetic testing for structural rearrangements (PGT-SR). Participants/materials, setting, methods We evaluated euploidy, aneuploidy and mosaicism rates reported in day 5 (n = 9560), day 6 (n = 4753) and day 7 (n = 262) blastocysts, stratified by SART-defined maternal age categories (&amp;lt;35, 35–37, 38–40, 41–42, &amp;gt;42). We further assessed the type and frequency of abnormalities reported in all blastocysts classified as clinically unsuitable, according to the day of biopsy. Finally, we examined the specific chromosomes affected in embryos diagnosed with a single uniform (n = 3882) or single mosaic (n = 518) abnormality. Main results and the role of chance The mean maternal age within our patient cohort was 39.9±3.7. Overall, slowly developing blastocysts were significantly more likely to be classified as clinically unsuitable (60.6%) compared to day 5 embryos (55.2%; p &amp;lt; 0.0001). This correlation was also observed when stratified by age, with the exception of the &amp;lt;35 age group (p = 0.25). Markedly, the risk of aneuploidy in slowly developing blastocysts became progressively higher with advancing maternal age (p &amp;lt; 0.0001). We did not observe any significant differences in the types of abnormalities diagnosed in slowly developing embryos compared to day 5 blastocysts. Nevertheless, abnormalities affecting all chromosomes were present at the blastocyst stage. Single trisomies and monosomies were the most frequent across all age groups, and were equally prevalent in day 5, 6 and 7 blastocysts. These most commonly affected chromosomes 16, 22, 21 and 15. We observed no significant differences in the incidence of segmental aneuploidies in relation to the day of biopsy, across all age groups. When considered separately, day 7 blastocysts presented with higher rates of structural aberrations, however low numbers limited statistical power. Finally, delayed blastocyst development was not associated with higher mosaicism rates (p = 0.79). Interestingly, single mosaic trisomies and monosomies were most frequently associated with chromosome 19. Limitations, reasons for caution Due to the retrospective nature of the study, full elucidation of all potential confounders may not be possible in all instances. The low number of day 7 blastocysts limited statistical power. As such, the results from day 6 and day 7 embryos were evaluated together. Wider implications of the findings: Our findings offer an important clinical resource for counselling patients of advanced maternal age. Maternal aging may be associated with a higher incidence of aneuploidy in slowly developing blastocysts. Nevertheless, extended culture increases the pool of biopsiable blastocysts, ultimately improving the chance of having a euploid embryo for transfer. Trial registration number NA

P–551 Blastocyst cohort size is not associated with embryo aneuploidy: comprehensive multi-centre data from current preimplantation genetic testing cycles

Abstract Study question Does blastocyst cohort size impact aneuploidy rates, evaluated by next generation sequencing (NGS)? Summary answer Embryo aneuploidy rates were independent of blastocyst cohort size across all patient ages. What is known already The effects of ovarian response on oocyte and embryo quality remain controversial. Several studies have proposed that a high response to ovarian stimulation may negatively impact oocyte competence. Alternatively, irrespective of maternal age, a poor ovarian response may potentially compromise embryo quality. Using blastocyst cohort size as an indirect measure of ovarian response, previous studies applying array comparative genomic hybridisation (aCGH) have demonstrated that the number of embryos available for biopsy does not impact embryo aneuploidy rates. Nevertheless, these findings remain to be confirmed in a comprehensive cohort, using current approaches for preimplantation genetic testing for aneuploidies (PGT-A). Study design, size, duration Retrospective, international, cohort study of 3998 patients from 16 clinics undergoing PGT-A from 2016–2020. We evaluated 11665 blastocysts, tested using trophectoderm (TE) biopsy and next generation sequencing (NGS). To eliminate bias of multiple treatments, we considered only the first PGT-A cycle for all patients. Both autologous and donation cycles were included in the analysis. Cycles were excluded if they utilised preimplantation genetic testing for monogenic disorders (PGT-M) or preimplantation genetic testing for structural rearrangements (PGT-SR). Participants/materials, setting, methods We evaluated aneuploidy and mosaicism rates, as well as the proportion of patients who had at least one euploid embryo suitable for transfer. Findings were stratified according to SART-defined maternal age groups, &amp;lt;35 (n = 698/2622 patients/blastocysts), 35–37 (n = 988/3141 patients/blastoycsts), 38–40 (n = 1447/3939 patients/blastocysts), 41–42 (653/1562 patients/blastocysts) and &amp;gt;42 (212/401 patients/blastocysts) and blastoycst cohort size (1–2, 3–5, 6–9 and 10 or more biopsied blastocysts). Main results and the role of chance The mean maternal age was 37.0±3.7. The overall embryo aneuploidy rate was 50.6% (5904/11665), while mosaicism was established in 4.0% (469/11665) of blastocysts. As expected, the proportion of aneuploid embryos increased steadily with advancing maternal age (31.8%, 41.5%, 58.4%, 71.2%, 87.8%; p &amp;lt; 0.0001), while mosaicism rates did not vary significantly (p = 0.2). Within each age group, we observed no association between the number of blastocysts biopsied and aneuploidy or mosaicism rates. However, as previously suggested, the chance of having at least one euploid embryo increased linearly with the number of embryos biopsied. We observed that young patients (&amp;lt;35) with 1–2 blastocysts had a 70.4% of having at least one embryo suitable for transfer, which increased to 96.4% and 99.2% with 3–5 and 6–9 blastocysts, respectively. Similar trends were observed in the 36–38 and 39–40 age groups. Patients in the 40–41 age group had a significantly lower chance of having a suitable embryo for transfer. Nevertheless, the chance increased from 27.2% with 1–2 embryos to 61.2% with 3–5 blastocysts. Patients with &amp;gt;10 embryos had at least one euploid embryo in 100% of cases, across all ages. Albeit, the numbers of patients within this category was low, and decreased significantly with advancing maternal age. Limitations, reasons for caution While blastocyst cohort size is considered to be an indirect measure of ovarian reserve, the number of oocytes retrieved was not evaluated. Our study only included the first PGT-A cycle for all patients. Subsequent, alterations in stimulation protocols may have resulted in an improved response in some patients. Wider implications of the findings: The comprehensive nature of the study, based on current PGT-A approaches and a large number of cycles across 16 centres increases clinical confidence in the notion that ovarian response is independent of embryo aneuploidy. Importantly, our findings may serve as a valuable clinical resource to guide patient counselling strategies. Trial registration number NA

Healthy Genetically Normal Live-Birth After Mosaic Chromosome 5 Embryo Transfer: A Case Report

Embryonic mosaicism is defined as two or more distinct cell lines within an embryo, which is originally developed from a zygote. Although the potential of mosaic embryos still remain unclear, recent reports have proved that mosaic embryo transfer can achieve healthy live-births. Up to now, there is no report of a live-birth having mosaic trisomy of full chromosome 5 following in-vitro fertilization (IVF). Our case is the first case proving that the transfer of medium-mosaicism embryo can result in a healthy live-birth. The couple are both carriers of balanced reciprocal translocations (46,XX,t(2;8)(p23;q24.3) and 46,XY,t(12;16)(q13.2;q23)). They had three IVF cycles combined with PGT-SR (Preimplantation Genetic Testing for Structural Rearrangement). A total of 18 blastocysts were biopsied and no euploid embryo was found. After the conselling, the patients chose to transfer a 40% mosaic trisomy chromosome 5 embryo. The follow-up pregnancy including prenatal diagnosis, amniocentesis and peripheral blood chromosome analysis of the newborn revealed no trisomy chromosome 5.