Mosaic embryo transfer after oocyte in vitro maturation in combination with non-invasive prenatal testing (NIPT)-first report of a euploid live birth

Mitochondrial DNA quantification correlates with the developmental potential of human euploid blastocysts but not with that of mosaic blastocysts

PURPOSE

We aimed to study the association between adjusted mtDNA levels in human trophectoderm biopsy samples and the developmental potential of euploid and mosaic blastocysts.

METHODS

We analyzed relative mtDNA levels in 2,814 blastocysts obtained from 576 couples undergoing preimplantation genetic testing for aneuploidy from June 2018 to June 2021. All patients underwent in vitro fertilization in a single clinic; the study was blinded-mtDNA content was unknown at the time of single embryo transfer. The fate of the euploid or mosaic embryos transferred was compared with mtDNA levels.

RESULTS

Euploid embryos had lower mtDNA than aneuploid and mosaic embryos. Embryos biopsied on Day 5 had higher mtDNA than those biopsied on Day 6. No difference was detected in mtDNA scores between embryos derived from oocytes of different maternal ages. Linear mixed model suggested that blastulation rate was associated with mtDNA score. Moreover, the specific next-generation sequencing platform used have a significant effect on the observed mtDNA content. Euploid embryos with higher mtDNA content presented significantly higher miscarriage rates and lower live birth rates, while no significant difference was observed in the mosaic cohort.

CONCLUSION

Our results will aid in improving methods for analyzing the association between mtDNA level and blastocyst viability.

Single-cell Sequencing Reveals Clearance of Blastula Chromosomal Mosaicism in In Vitro Fertilization Babies

Although chromosomal mosaic embryos detected by trophectoderm (TE) biopsy offer healthy embryos available for transfer, high-resolution postnatal karyotyping and chromosome testing of the transferred embryos are insufficient. Here, we applied single-cell multi-omics sequencing for seven infants with blastula chromosomal mosaicism detected by TE biopsy. The chromosome ploidy was examined by single-cell genome analysis, with the cellular identity being identified by single-cell transcriptome analysis. A total of 1616 peripheral leukocytes from seven infants with embryonic chromosomal mosaicism and three control ones with euploid TE biopsy were analyzed. A small number of blood cells showed copy number alterations (CNAs) on seemingly random locations at a frequency of 0%-2.5% per infant. However, none of the cells showed CNAs that were the same as those of the corresponding TE biopsies. The blastula chromosomal mosaicism may be fully self-corrected, probably through the selective loss of the aneuploid cells during development, and the transferred embryos can be born as euploid infants without mosaic CNAs corresponding to the TE biopsies. The results provide a new reference for the evaluations of transferring chromosomal mosaic embryos in certain situations.

Are tri-pronuclear embryos that show two normal-sized pronuclei and additional smaller pronuclei useful for embryo transfer?

Purpose

This study aimed to analyze whether tripronuclear (3PN) zygotes, with two normal‐sized PNs and an additional smaller PN (2.1PN), can be used for embryo transfer.

Method(s)

A retrospective embryo cohort study was conducted on 695 patients who underwent intracytoplasmic sperm injection treatment. Blastocyst formation rates were compared between 2.1PN and 2PN zygotes and PGT‐A analysis was performed on 15 blastocysts derived from 2.1PN zygotes.

Result(s)

Blastocyst formation rates were comparable between 2.1PN (43.8%) and 2PN zygotes (54.8%; p = 0.212). The rates of blastocysts with good morphology derived from 2.1 PN and 2PN zygotes were 18.8% and 25.5%, respectively. No significant differences were detected (p = 0.383). All of the analyzed blastocysts were diploid; however, 13 of these were found to be aneuploid, with a further two being mosaic.

Conclusion

Our results suggest that 2.1PN embryos can reach blastocyst stage. These blastocysts were diploid, however, predominantly aneuploid, and therefore could not be used for embryo transfer.

A Non-invasive Chromosome Screening Strategy for Prioritizing in vitro Fertilization Embryos for Implantation

Preimplantation genetic testing for aneuploidy (PGT-A) is widely used to select embryos having normal ploidy for transfer, but they require an invasive embryo biopsy procedure that may cause harm to the embryos and offspring. Therefore, a non-invasive approach to select embryos with normal ploidy for implantation is highly demanded. Non-invasive chromosome screening (NICS) methods have been proposed and applied in clinical practices, but a large-scale validation versus invasive preimplantation genetic testing (PGT) and the whole embryo ploidy has not yet been reported. In this study, by using the whole embryo as a gold standard, we validated NICS assay in a total of 265 donated human embryos and compared its performance with conventional trophectoderm (TE) biopsy PGT. The NICS assay showed promising performance, which is comparable to PGT-TE [sensitivity: 87.36 versus 89.66%; specificity: 80.28 versus 82.39%; negative predictive value (NPV): 91.2 versus 92.86%; positive predictive value (PPV): 73.08 versus 75.73%]. Additionally, NICS provides a scoring system for prioritizing embryo: embryos can be categorized into three groups with euploid prediction probabilities of 90.0, 27.8, and 72.2% for group euploid (A), aneuploid (B), and multiple abnormal chromosomes (MAC) (C), respectively. When an addition of TE assay is provided as a secondary validation, the accuracy significantly increases from 72.2 to 84.3% for group B and from 27.8 to 83.3% for group C. Our results suggest that NICS is a good rule in assay for identifying chromosomal normal embryos for transfer and might serve as a non-invasive approach for prioritizing embryos instead of preventing transfer of aneuploid and MAC embryos. It will help to ensure the safety of offspring and efficient utilization of embryos.

The "mosaic" embryo: misconceptions and misinterpretations in preimplantation genetic testing for aneuploidy

Preimplantation genetic testing for aneuploidy (PGT-A) remains one of the most controversial topics in reproductive medicine. With more than 40% of in vitro fertilization cycles in the United States reportedly involving PGT, both those in favor of and those opposed to PGT-A have significant interest in the efficacy of PGT-A. Ongoing issues include what patient population, if any, benefits from PGT-A, the true frequency of chromosomal mosaicism, whether embryonic aneuploidies self-correct, and how practitioners manage embryos designated as "mosaic." This review addresses several misconceptions and misinterpretations of data surrounding the genetic analysis and prediction of mosaicism in the preimplantation embryo.

Generation of viable blastocysts from discarded human cleavage embryos

Background

While a relationship between embryo morphology, developmental ability, and genetic integrity exists, the selection of embryos with higher implantation potential remains a major challenge in assisted reproductive technology (ART). This study investigated blastocyst developmental competence and euploidy status in human embryos that had been classed as too poor quality to transfer (ET) or cryopreserve at the cleavage stage.

Embryos were divided into three groups. Group 1 (n = 41) included good quality embryos from candidates of preimplantation genetic testing for aneuploidy (PGT-A). Groups II and III were the “rejected” supernumerary embryos, defined as suboptimal for ET or vitrification after morphological examination, with embryos randomly divided between the groups. Group II embryos (n = 31) were cultured up to the day 3 cleavage stage, when they were biopsied and fixed. Group III embryos (n = 27) were cultured up to the day 5 blastocyst stage, when they were evaluated for morphology and chromosomal status. Chromosomal status in all groups was assessed by multi-color fluorescence in situ hybridization (FISH) for chromosomes 13, 18, 21, X, and Y.

Results

Euploidy rates in groups I, II, and III were 56.1%, 38.7%, and 55.5 %, respectively. Among the blastocysts that developed from “rejected” embryos, 59.3% were classed as good quality. The most frequent chromosomal aneuploidy was related to the sex chromosome (22.2%). The mosaicism rate was not significantly different between the group II and III embryos (25.8% vs. 37.0%, p = 0.28).

Conclusion

In conclusion, surplus poor-quality embryos rejected from clinical utilization at the cleavage stage may develop into viable blastocysts with normal chromosomal status for at least 5 chromosomes. Recovery of euploidy during poor-quality embryo transition from cleavage stage to blastocyst could provide an alternative choice for ET.

Clinical Outcomes of Single Mosaic Embryo Transfer: High-Level or Low-Level Mosaic Embryo, Does it Matter?

Recently, reports showed that embryos identified as mosaic after preimplantation genetic testing for aneuploid (PGT-A) could result in live birth with lower pregnancy and higher pregnancy loss rates compared with euploid embryos. However, the effects of mosaicism level on reproductive outcomes remain controversial. This study aimed to examine the level of mosaicism on pregnancy outcomes. Single mosaic embryo transfer was offered to 108 women who only had mosaic embryos. Mosaic embryos were labeled by utilizing next generation sequencing (NGS) based PGT-A for day 5/6 trophectoderm (TE)biopsies. TE biopsies containing < 50% abnormal cells were classified as low-level mosaicism and ≥ 50% as high-level mosaicism. To further confirm the concordance of chromosome constitution between TE and inner cell mass (ICM), 41 remaining embryos designated as mosaic blastocysts donated for research were also analyzed. Comparable live birth rate (LBR) but higher miscarriage rate (MR) was found in the high-level group. (LBR: low vs. high: 44.5% vs. 36%; p = 0.45, MR: low vs. high: 5.1% vs. 30.7%; p = 0.012). Analyses of TE and ICM from the remaining mosaic blastocysts show a poor concordance. This preliminary study demonstrated that high-level mosaic embryos could result in comparable LBR but higher MR.

National mosaic embryo transfer practices: a survey

BACKGROUND

The growing use of preimplantation genetic testing with in vitro fertilization has provided clinicians with more information about the genetics of embryos. Embryos, however, sometimes result with a mixed composition of both aneuploid and euploid cells, called mosaic embryos. The interpretation of these results has varied, leading some clinicians to transfer mosaic embryos and some opt not to. In addition, laboratories providing preimplantation genetic testing for aneuploidy have differing thresholds for determining an embryo aneuploid, mosaic, or euploid. Overall practice patterns for mosaic embryo transfer practices in the United States are unknown.

OBJECTIVE(S)

The objectives of the study were to characterize national mosaic embryo transfer practices, including the use of preimplantation genetic testing for aneuploidy, prior history of transferring mosaic embryos, thresholds for determining mosaicism, and willingness to transfer mosaic embryos among assisted reproductive technology clinics in the United States.

STUDY DESIGN

A 14 question online survey assessing current use of preimplantation genetic testing for aneuploidy, thresholds for determining mosaicism, and clinic experience and willingness to transfer mosaic embryos was e-mailed to 405 assisted reproductive technology clinics across the United States. Descriptive statistics and logistic regression were used to analyze survey responses and identify clinical factors associated with reporting having ever transferred a mosaic embryo.

RESULTS

Of the 405 US assisted reproductive technology clinics contacted, 252 (62.2%) completed a survey, including 157 private (62.3%), 55 academic (21.8%), and 40 hybrid (15.9%) clinics. Most clinics (168, 66.7%) reported conducting preimplantation genetic testing for aneuploidy on less than 50% of all in vitro fertilization cycles. The most common type of preimplantation genetic testing for aneuploidy technology used was next-generation sequencing at 88.9%. Ninety-one clinics (36.1%) receive mosaicism data on their preimplantation genetic testing for aneuploidy report; the most common thresholds for determining embryo aneuploidy and euploidy by clinics' primary genetics laboratories were <20% normal (36.3%) and >80% normal (46.2%), respectively. Thirty-nine (42.9%) of the 91 have transferred and 57 (62.6%) would transfer a mosaic embryo. Nearly 40% of clinics were unsure about their thresholds for mosaic transfer and one fourth of clinics reported they had no threshold. Private (odds ratio, 1.0, 95% confidence interval, 0.5-1.8) and hybrid (odds ratio, 0.9, 95% confidence interval, 0.4-2.1) clinics were just as likely as academic clinics to report having transferred a mosaic embryo. Clinics in the northeastern United States were more likely to have transferred a mosaic embryo than clinics in other regions (odds ratio, 1.5, 95% confidence interval, 0.9-2.7). Most clinics (72.6%) report they do not have a unique consent for transfer of mosaic embryos.

CONCLUSION

There is uncertainty and variability in the transfer practices of mosaic embryos and classification of mosaicism among US assisted reproductive technology clinics. These findings provide an opportunity to establish mosaicism thresholds and create standardized guidelines for transferring mosaic embryos.

Minimizing mosaicism: assessing the impact of fertilization method on rate of mosaicism after next-generation sequencing (NGS) preimplantation genetic testing for aneuploidy (PGT-A)

PURPOSE

Advances in preimplantation genetic testing (PGT) have led to practice changes in assisted reproductive technologies (ART), enabling fertility centers to transfer single embryos while maintaining excellent ongoing pregnancy rates, reducing miscarriage rates, and dramatically reducing ART-associated multiple pregnancies. The introduction of next-generation sequencing (NGS) allows PGT laboratories to assess for embryo mosaicism-although the true incidence and reproductive potential of predicted mosaic embryos are controversial. Due to concern for genetic contamination from other spermatozoa, most reference laboratories require use of intracytoplasmic sperm injection (ICSI) for single gene preimplantation genetic diagnosis (PGT-M). However, in PGT for aneuploidy (PGT-A), conventional insemination (IVF) is typically permissible. The purpose of this study was to evaluate rates of euploid, aneuploid, and mosaic in trophectoderm biopsy samples from embryos in IVF versus ICSI PGT-A cycles. Secondary aims were to assess sex ratio, and subtypes of aneuploidy and mosaicism in IVF versus ICSI PGT-A cycles.

METHODS

We performed a retrospective review of women undergoing PGT-A at a single academic fertility center from July 1, 2015, to September 1, 2017. In all cycles, PGT-A was performed via trophectoderm biopsy on day 5 or 6 and analyzed using NGS at a single reference lab. We collected and compared patient demographics, fertility testing, cycle characteristics, and PGT-A outcomes between IVF and ICSI cycles.

RESULTS

Three hundred two PGT-A cycles were included for analysis: 75 IVF and 227 ICSI cycles, resulting in 251 IVF and 724 ICSI biopsied blastocysts. Mean oocyte age of included cycles was 38.6 years (IVF) and 38.5 years (ICSI), p = 0.85. Baseline characteristics of IVF and ICSI PGT-A cycles were similar with the exception of semen parameters: IVF cycles had higher sperm concentration and total motility compared to ICSI cycles. PGT-A outcomes did not differ between IVF and ICSI cycles: euploid 27.9% (IVF) versus 30% (ICSI); aneuploid 45.4% (IVF) versus 43.1% (ICSI); no result 4.4% (IVF) versus 6.2% (ICSI). Though not significant, we identified a trend toward higher rate of mosaicism in IVF (25.9%) versus ICSI (20.9%). Among mosaic embryos, a lower percentage of simple mosaic embryos resulted from IVF (53.8%) versus ICSI (70.2%). Among aneuploid embryos, a non-significant higher percentage of complex aneuploidy resulted from IVF (16.3%) versus ICSI (9%). IVF resulted in a non-significant higher proportion of cycles with no transferrable embryos (42.7%) versus ICSI (36.6%). Numerical and sex chromosome involvement in mosaicism and aneuploidy were similar between IVF and ICSI cycles.

CONCLUSION

IVF and ICSI NGS PGT-A have similar rates of euploid, aneuploid, and no result embryos, though IVF may result in higher rates of mosaicism and demonstrates differences in proportions of mosaic and aneuploid subtypes compared to ICSI. ICSI may be preferable to conventional insemination to minimize the rate of mosaic results in NGS PGT-A cycles.