Concordance of various chromosomal errors among different parts of the embryo and the value of re-biopsy in embryos with segmental aneuploidies

The correlation between blastocyst morphological parameters and chromosomal euploidy, aneuploidy and other chromosomal abnormalities following pre-implantation genetic testing-a single center retrospective study

PURPOSE

To examine the association between blastocyst morphology and chromosomal status utilizing pre-implantation genetic testing for aneuploidy (PGT-A).

METHODS

A single-center retrospective cohort study including 169 in-vitro fertilization cycles that underwent PGT-A using Next Generation Sequencing (2017-2022). Blastocysts were morphologically scored based on Gardner and Schoolcraft's criteria. Chromosomal analysis results included: euploid; aneuploid (single or double); segmental; mosaic; and complex (≥ 3 chromosome abnormalities). We examined associations between morphological parameters and chromosomal statuses of biopsied embryos utilizing multivariate logistic regression.

RESULTS

Overall, 855 blastocysts underwent PGT-A (PGT-A alone: N = 804; unaffected PGT for monogenic disease (PGT-M) embryos along with PGT-A: N = 51). Of these, 826 were successfully analyzed, with 321 euploid embryos (38.86%). Various morphological parameters (embryo quality, inner cell mass (ICM), trophectoderm (TE), and expansion stage) were more frequent within the double (n = 72, 8.72%), complex (n = 97, 11.74%), mosaic (n = 139, 16.83%), and segmental aneuploidy (n = 28, 3.39%) groups, with similar associations between different morphological parameters and single aneuploidy (n = 169, 20.46%). Utilizing multivariate logistic regression, higher expansion, embryo quality, and TE and ICM grades, were associated with increased odds of euploidy (versus non-euploidy). Higher expansion was a positive predictor of single versus double aneuploidy (aOR 2.94, 95% CI 1.52-5.56, p = 0.001); and higher ICM grade was a positive predictor of single versus complex aneuploidy (aOR 2.86, 95% CI 1.15-7.12, p = 0.024). No morphological parameter was found to be associated with single versus mosaic aneuploidy.

CONCLUSION

Various morphological parameters are associated with euploidy and different aneuploidy statuses of pre-implantation blastocysts. These findings may aid in the selection of the assumed best chromosomally structured blastocyst for transfer when PGT-A is not performed.

Healthy live births achieved from embryos diagnosed as non-mosaic segmental aneuploid

PURPOSE

To investigate pregnancy outcomes resulting from transfer of embryos with non-mosaic (NM) segmental aneuploid (SA) results following preimplantation genetic testing for aneuploidy (PGT-A).

METHODS

All patients who underwent frozen embryo transfer (FET) of at least one embryo with a NM-SA between March 2021 and April 2024 were retrospectively reviewed. Primary outcomes included live birth rate (LBR) and results of prenatal diagnosis. Embryos with NM-SA results were also compared to those with NM whole chromosome aneuploid (WCA) and mosaic SA results.

RESULTS

Out of 25 NM-SA embryos transferred, the LBR was 24%. Prenatal diagnosis by amniocentesis and/or chorionic villus sampling was performed in 3/6 pregnancies, and results were normal. Embryos with duplications produced more live births compared to those with deletions. NM-SA embryos had a significantly higher ongoing pregnancy (OP)/LBR compared to embryos with NM-WCA results and a significantly lower OP/LBR compared to embryos with mosaic SA results; however, when compared to embryos with high-level SA mosaicism > 40%, the OP/LBR was not significantly different.

CONCLUSION

Embryos with NM-SAs can result in euploid live births, albeit at reduced rates compared to those with mosaic SAs. These data can be used to aid in patient counseling about PGT-A results and embryo transfer decisions.

Assessing the necessity of screening ≤5 Mb segmental aneuploidy in routine PGT for aneuploidies

RESEARCH QUESTION

Does routine clinical practice require an increase in the resolution of preimplantation genetic testing for aneuploidies (PGT-A) to detect segmental aneuploidies ≤5 Mb?

DESIGN

This retrospective study analysed 963 trophectoderm biopsies from 346 couples undergoing PGT between 2019 and 2023. Segmental aneuploidies ≥1 Mb were reported. The characteristics, clinical interpretation and concordance of segmental aneuploidies ≤5 Mb were analysed.

RESULTS

The incidence of segmental aneuploidies was 15.1% (145/963) in blastocysts, with segmental aneuploidies of ≤5 Mb accounting for 2.3% (22/963). The size of the segmental aneuploidies showed a skewed distribution. Segmental aneuploidies ≤5 Mb were found to occur more frequently on the q arm of the chromosome, compared with the p arm. Losses of ≤5 Mb segmental aneuploidies were more prevalent than gains, with 17 deletions compared with 5 duplications. Of the segmental aneuploidies, 63.6% (14/22) ≤5 Mb were de novo, and 50.0% (7/14) of de-novo segmental aneuploidies were pathogenic/likely pathogenic (P/LP) copy number variations, accounting for 0.7% of 963 blastocysts. For blastocysts carrying ≤5 Mb segmental aneuploidies, a re-analysis of back-up biopsy samples showed that 35.7% of de-novo segmental aneuploidies (5/14) were not detected in the back-up samples. Cases were reported in which prenatal diagnosis (amniocentesis) revealed the absence of embryonic ≤5 Mb segmental aneuploidies detected at the blastocyst stage.

CONCLUSIONS

The incidence of P/LP de-novo ≤5 Mb segmental aneuploidies in human blastocysts is extremely low. There is no compelling need to increase the resolution of PGT-A to 5 Mb in routine clinical practice.

Effect of freeze-thawing, cell collection, and laser irradiation cycles on mosaicism occurrence in preimplantation genetic testing for aneuploidy

OBJECTIVE

In preimplantation genetic testing for aneuploidy, opinions regarding the handling of mosaic embryos vary. In this study, we aimed to investigate the effects of freeze-thawing, the number of cells obtained, and the number of laser irradiation cycles on the degree of embryonic mosaicism.

STUDY DESIGN

This study was conducted in three parts. First, we classified specimens into the normal biopsy (control) (119 patients, 304 blastocysts) and thawed-biopsy (TB group) (26 patients, 72 blastocysts)) groups. The control and TB groups were then classified into three categories (euploidy, mosaic and aneuploidy) according to next-generation sequencing (NGS) results, and the number of cells collected and laser irradiation cycles were compared for each category. Subsequently, the effects of differences in the number of cells collected and laser irradiation cycles on NGS results were investigated in the control and TB groups. Finally, data on cell collection and laser irradiation cycles and NGS analysis results for the groups were compared.

RESULTS

The TB group had a significantly higher incidence of chromosomal mosaicism than the control group. Neither the number of cells collected nor the laser irradiation cycles affected the percentage of chromosomal mosaicism. However, the freeze-thaw process increased the occurrence of mosaicism.

CONCLUSIONS

This study showed that repeated freeze-thaw cycles increase the incidence of mosaicism, but the embryos are not aneuploid and are therefore suitable for transfer.

Re-Examination of PGT-A Detected Genetic Pathology in Compartments of Human Blastocysts: A Series of 23 Cases

Background: In recent years, preimplantation genetic testing for aneuploidies (PGT-A) has become widespread in assisted reproduction. However, contrary to expectations, PGT-A does not significantly improve the clinical outcomes of assisted reproductive technologies. One of the underlying reasons is the discordance between the PGT-A results and the true chromosomal constitution of the blastocyst. In this case series, we re-examined the PGT-A results in trophectoderm (TE) re-biopsies and in the two isolated blastocyst compartments-the TE and the inner cell mass (ICM). Methods: This study enrolled 23 human blastocysts from 17 couples who were referred for assisted reproduction. The blastocysts were unsuitable for uterine transfer due to the chromosomal imbalance revealed by PGT-A using array comparative genomic hybridization (aCGH) (n = 11) or next-generation sequencing (NGS) (n = 12). The re-examination of the PGT results involved two steps: (1) a TE re-biopsy with subsequent aCGH and (2) blastocyst separation into the TE and the ICM with a subsequent cell-by-cell analysis of each isolated compartment by fluorescence in situ hybridization (FISH) with the DNA probes to chromosomes 13, 16, 18, 21, and 22 as well as to the PGT-A detected imbalanced chromosomes. Results: In 8 out of 23 cases, the PGT-A results were concordant with both the re-biopsy and the isolated TE and ICM analyses. The latter included the diagnoses of full non-mosaic aneuploidies (five cases of trisomies and two cases of monosomies). In one case, the results of PGT-A, aCGH on the TE re-biopsy, and FISH on the isolated TE showed Xp tetrasomy, which contrasted with the FISH results on the isolated ICM, where this chromosomal pathology was not detected. This case was classified as a confined mosaicism. In 4 out of 23 cases, the results were partially discordant. The latter included one case of trisomy 12, which was detected as non-mosaic by PGT-A and the re-biopsy and as mosaic by FISH on the isolated TE and ICM. This case was classified as a true mosaicism with a false negative PGT-A result. In 11 out of 23 cases, the re-examination results were not concordant with the PGT-A results. In one of these discordant cases, non-mosaic tetraploidy was detected by FISH in the isolated TE and ICM, whereas the PGT-A and the TE re-biopsy failed to detect any abnormality, which advocated for their false negative result. In two cases, the re-examination did not confirm full aneuploidies. In eight cases, full or partial mosaic aneuploidies as well as chaotic mosacism were not confirmed in the isolated TE nor the isolated ICM. Thus, in 47.8% of cases, the PGT-A results did not reflect the true chromosomal constitution of a blastocyst. Conclusions: The PGT results may have different prognostic value in the characterization of the chromosomal constitution of a blastocyst. The detected non-mosaic aneuploidies have the highest prognostic value. In stark contrast, most PGT-identified mosaic aneuploidies fail to characterize the true chromosomal constitution of a blastocyst. Once detected, a differential diagnosis is needed.

Blinded rebiopsy and analysis of noneuploid embryos with 2 distinct preimplantation genetic testing platforms for aneuploidy

OBJECTIVE

To determine how often a noneuploid result from a single trophectoderm (TE) biopsy tested with the next-generation sequencing (NGS)-based preimplantation genetic testing for aneuploidy (PGT-A) is concordant with rebiopsies tested with a single-nucleotide polymorphism (SNP) array-based PGT-A platform.

DESIGN

Blinded prospective cohort study.

SETTING

University-affiliated fertility center.

PATIENT(S)

One hundred blastocysts were chosen from donated samples; on TE biopsy with NGS-based PGT-A, 40 had at least one whole chromosome full copy number aneuploidy alone, 20 had a single whole chromosome intermediate copy number ("whole chromosome mosaic"), 20 had a single full segmental aneuploidy (segA), and 20 had a single segmental intermediate copy number ("segmental mosaic").

INTERVENTIONS

Four rebiopsies were collected from each embryo: 3 TE biopsies and the remaining embryo. Each rebiopsy was randomized, blinded, and assessed with an SNP array-based PGT-A platform that combines copy number and allele ratio analyses, without mosaicism reporting.

MAIN OUTCOME MEASURE(S)

Concordance between the NGS result and rebiopsy results and within each embryo's blinded rebiopsy results.

RESULT(S)

Next-generation sequencing-diagnosed whole chromosome aneuploidy (WCA) was reconfirmed in 95% (95% confidence interval [CI], 83%-99%) of embryos; 2 embryos with NGS-diagnosed WCA were called euploid on all conclusive rebiopsies. Among embryos with NGS-diagnosed whole chromosome mosaicism, 35% (95% CI, 15%-59%) were called euploid and 15% (95% CI, 3%-38%) were called whole chromosome aneuploid on all conclusive rebiopsies. A total of 30% (95% CI, 12%-54%) of embryos with NGS-diagnosed segA and 65% (95% CI, 41%-85%) of embryos with NGS-diagnosed segmental mosaicism were called euploid on all conclusive rebiopsies. In total, 13% (95% CI, 6%-25%) of embryos with NGS-diagnosed full copy number aneuploidy and 50% (95% CI, 34%-66%) of embryos with NGS-diagnosed mosaicism had uniformly euploid SNP results. Conversely, all embryos with at least one noneuploid SNP result (n = 72) either had SNP-diagnosed aneuploidy on another rebiopsy from the same embryo or NGS-diagnosed aneuploidy/mosaicism involving the same chromosome.

CONCLUSION(S)

Next-generation sequencing-diagnosed WCA is highly concordant with rebiopsies tested with an SNP array-based PGT-A; however, whole chromosome mosaicism, segA, and segmental mosaicism are less concordant, reinforcing that embryos with these results may have reproductive potential and be suitable for transfer.

Conventional IVF is feasible in preimplantation genetic testing for aneuploidy

PURPOSE

To investigate the feasibility of the application of conventional in vitro fertilization (cIVF) for couples undergoing preimplantation genetic testing for aneuploidies (PGT-A) with non-male factor infertility.

METHODS

To evaluate the efficiency of sperm whole-genome amplification (WGA), spermatozoa were subjected to three WGA protocols: Picoplex, ChromInst, and multiple displacement amplification (MDA). In the clinical studies, 641 couples who underwent PGT-A treatment for frozen embryos between January 2016 and December 2021 were included to retrospectively compare the chromosomal and clinical outcomes of cIVF and intracytoplasmic sperm injection (ICSI). Twenty-six couples were prospectively recruited for cIVF and PGT-A treatment between April 2021 and April 2022; parental contamination was analyzed in biopsied samples; and 12 aneuploid embryos were donated to validate the PGT-A results.

RESULTS

Sperm DNA failed to amplify under Picoplex and ChromInst conditions but could be amplified using MDA. In frozen PGT-A cycles, no significant differences in the average rates of euploid, mosaic, and aneuploid embryos per cycle between the cIVF-PGT-A and ICSI-PGT-A groups were observed. The results of the prospective study that recruited couples for cIVF-PGT-A treatment showed no paternal contamination and one case of maternal contamination in 150 biopsied trophectoderm samples. Among the 12 donated embryos with whole-chromosome aneuploidy, 11 (91.7%) presented uniform chromosomal aberrations, which were in agreement with the original biopsy results.

CONCLUSIONS

Under the Picoplex and ChromInst WGA protocols, the risk of parental contamination in the cIVF-PGT-A cycles was low. Therefore, applying cIVF to couples with non-male factor infertility who are undergoing PGT-A is feasible.

Chromosomal Aberrations As a Biological Phenomenon in Human Embryonic Development

Frequent chromosomal abnormalities are a distinctive feature of early embryonic development in mammals, especially humans. Aneuploidy is considered as a contributing factor to failed embryo implantation and spontaneous abortions. In the case of chromosomal mosaicism, its effect on the potency of embryos to normally develop has not been sufficiently studied. Although, a significant percentage of chromosomal defects in early human embryos are currently believed to be associated with the features of clinical and laboratory protocols, in this review, we focus on the biological mechanisms associated with chromosomal abnormalities. In particular, we address the main events in oocyte meiosis that affects not only the genetic status of an unfertilized oocyte, but also further embryo viability, and analyze the features of first cleavage divisions and the causes of frequent chromosomal errors in early embryonic development. In addition, we discuss current data on self-correction of the chromosomal status in early embryos.

Comparison of euploid blastocyst expansion with subgroups of single chromosome, multiple chromosome, and segmental aneuploids using an AI platform from donor egg embryos

PURPOSE

This retrospective observational study compares how different classes of blastocyst genotypes from egg donor cycles differentially blastulate and expand using a standard assay.

METHODS

Quantitative measurements of expansion utilized a customized neural network that segments all sequential time-lapse images during the first 10 h of expansion.

RESULTS

Analyses were performed using two developmental time perspectives using time-lapse imaging. The first was the time to blastocyst formation (tB), which broadly reflects variations in developmental rate. Euploidy peaked at 100-115 h from fertilization. In contrast, aneuploidy peaks flanked this interval bi-modally. These distributions limit ploidy discrimination based upon traditional standard grading features when assessed in real time. In contrast, from the second perspective of progressive blastocyst expansion that is normalized to each individual blastocyst's tB time, euploidy was significantly increased at expansion values > 20,000µ2 across all tB intervals studied. A Cartesian coordinate plot graphically summarizes information useful to rank order blastocysts within cohorts for transfer. Defined aneuploidy subgroups, distinguished by the number and complexity of chromosomes involved, also showed distributive differences from both euploids and from each other. A small subset of clinically significant trisomies did not show discriminating features separating them from other euploids.

CONCLUSION

A standard assay of blastocyst expansion normalized to each individual blastocyst's time of blastocyst formation more usefully discriminates euploidy from aneuploidy than real-time expansion comparisons using absolute developmental time from fertilization.

What proportion of embryos should be considered for transfer following a mosaic diagnosis? A study of 115 clinics from a central diagnostic laboratory

PURPOSE

The aim of this study is to identify what proportion of mosaic embryo diagnoses should be considered for transfer, and thereby assess the impact on patient cases.

METHODS

We categorised mosaic embryos into 3 groups; high, medium and low priority for transfer based on the percentage of biopsy sample being aneuploid and the chromosomes involved. The categories were applied to those patients that had no euploid embryo diagnoses but 1 or more mosaic embryos identified as mosaic available after PGT-A.

RESULTS

In total, 6614 PGT-A cases from 115 clinics and a single diagnostic laboratory were reviewed. Further, 1384 [20.9%] cases only had aneuploid embryos, 4538 [68.6%] cases had one or more euploid embryos and 692 [10.5%] cases had no euploid and one or more mosaic embryo. The mosaic embryos in the no euploid, one or more mosaic group, when reviewed using priorities, resulted in: 111 [1.7%] of cases having at least one high priority mosaic available. 184 [2.8%] of cases having no high priority but at least one medium priority mosaic available. 397 [6.0%] of cases only having low priority mosaic embryos available.

CONCLUSION

Based on this data, embryos identified as mosaic will only be considered for transfer in the first instance for around 4.5% (when taking high and medium priority and excluding low priority cases) of all PGT-A cases.

Segmental aneuploid hotspots identified across the genome concordant on reanalysis

The aim of this study was to characterize a large set of full segmental aneuploidies identified in trophectoderm (TE) biopsies and evaluate concordance in human blastocysts. Full segmental aneuploid errors were identified in TE biopsies (n = 2766) from preimplantation genetic testing for aneuploid (PGT-A) cycles. Full segmental deletions (n = 1872; 66.1%) presented twice as many times as duplications (n = 939; 33.9%), mapped more often to the q-arm (n = 1696; 61.3%) than the p-arm (n = 847; 31.0%) or both arms (n = 223; 8.1%; P < 0.05), and were eight times more likely to include the distal end of a chromosome than not (P < 0.05). Additionally, 37 recurring coordinates (each ≥ 10 events) were discovered across 17 different chromosomes, which were also significantly enriched for distal regions (P = 4.1 × 10-56). Blinded concordance analysis of 162 dissected blastocysts validated the original TE PGT-A full segmental result for a concordance of 96.3% (n = 156); remaining dissected blastocysts were identified as mosaic (n = 6; 3.7%). Origin of aneuploid analysis revealed full segmental aneuploid errors were mostly paternally derived (67%) in contrast to whole chromosome aneuploid errors (5.8% paternally derived). Errors from both parental gametes were observed in 6.5% of aneuploid embryos when multiple whole chromosomes were affected. The average number of recombination events was significantly less in paternally derived (1.81) compared to maternally derived (3.81) segmental aneuploidies (P < 0.0001). In summary, full segmental aneuploidies were identified at hotspots across the genome and were highly concordant upon blinded analysis. Nevertheless, future studies assessing the reproductive potential of full (non-mosaic) segmental aneuploid embryos are critical to rule out potential harmful reproductive risks.

Segmental aneuploidies with 1 Mb resolution in human preimplantation blastocysts

PURPOSE

This study aimed to investigate the spectrum and characteristics of segmental aneuploidies (SAs) of <10 megabase (Mb) length in human preimplantation blastocysts.

METHODS

Preimplantation genetic testing for aneuploidy was performed in 15,411 blastocysts from 5171 patients using a validated 1 Mb resolution platform. The characteristics and spectrum of SAs, including the incidence, sizes, type, inheritance pattern, clinical significance, and embryo distribution, were studied.

RESULTS

In total, 6.4% of the 15,411 blastocysts carried SAs of >10 Mb, 4.9% of embryos had SAs ranging between 1 to 10 Mb, and 84.3% of 1 to 10 Mb SAs were <5 Mb in size. Inheritance pattern analysis indicated that approximately 63.8% of 1 to 10 Mb SAs were inherited and were predominantly 1 to 3 Mb in size. Furthermore, 18.4% of inherited SAs and 51.9% de novo 1 to 10 Mb SAs were pathogenic or likely pathogenic (P/LP). Different from whole-chromosome aneuploidies, reanalysis indicated that 50% of the de novo 1 to 10 Mb SAs and 70% of the >10 Mb SAs arose from mitotic errors.

CONCLUSION

Based on the established platform, 1 to 10 Mb SAs are common in blastocysts and include a subset of P/LP SAs. Inheritance pattern analysis and clinical interpretation based on the American College of Medical Genetics and Genomics/Association for Molecular Pathology guidelines contributed to determine the P/LP SAs.

ESHRE survey results and good practice recommendations on managing chromosomal mosaicism

STUDY QUESTION

How should ART/preimplantation genetic testing (PGT) centres manage the detection of chromosomal mosaicism following PGT?

SUMMARY ANSWER

Thirty good practice recommendations were formulated that can be used by ART/PGT centres as a basis for their own policy with regards to the management of ‘mosaic’ embryos.

WHAT IS KNOWN ALREADY

The use of comprehensive chromosome screening technologies has provided a variety of data on the incidence of chromosomal mosaicism at the preimplantation stage of development and evidence is accumulating that clarifies the clinical outcomes after transfer of embryos with putative mosaic results, with regards to implantation, miscarriage and live birth rates, and neonatal outcomes.

STUDY DESIGN, SIZE, DURATION

This document was developed according to a predefined methodology for ESHRE good practice recommendations. Recommendations are supported by data from the literature, a large survey evaluating current practice and published guidance documents. The literature search was performed using PubMed and focused on studies published between 2010 and 2022. The survey was performed through a web-based questionnaire distributed to members of the ESHRE special interest groups (SIG) Reproductive Genetics and Embryology, and the ESHRE PGT Consortium members. It included questions on ART and PGT, reporting, embryo transfer policy and follow-up of transfers. The final dataset represents 239 centres.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The working group (WG) included 16 members with expertise on the ART/PGT process and chromosomal mosaicism. The recommendations for clinical practice were formulated based on the expert opinion of the WG, while taking into consideration the published data and results of the survey.

MAIN RESULTS AND THE ROLE OF CHANCE

Eighty percent of centres that biopsy three or more cells report mosaicism, even though only 66.9% of all centres have validated their technology and only 61.8% of these have validated specifically for the calling of chromosomal mosaicism. The criteria for designating mosaicism, reporting and transfer policies vary significantly across the centres replying to the survey. The WG formulated recommendations on how to manage the detection of chromosomal mosaicism in clinical practice, considering validation, risk assessment, designating and reporting mosaicism, embryo transfer policies, prenatal testing and follow-up. Guidance is also provided on the essential elements that should constitute the consent forms and the genetic report, and that should be covered in genetic counselling. As there are several unknowns in chromosomal mosaicism, it is recommended that PGT centres monitor emerging data on the topic and adapt or refine their policy whenever new insights are available from evidence.

LIMITATIONS, REASONS FOR CAUTION

Rather than providing instant standardized advice, the recommendations should help ART/PGT centres in developing their own policy towards the management of putative mosaic embryos in clinical practice.

WIDER IMPLICATIONS OF THE FINDINGS

This document will help facilitate a more knowledge-based approach for dealing with chromosomal mosaicism in different centres. In addition to recommendations for clinical practice, recommendations for future research were formulated. Following up on these will direct research towards existing research gaps with direct translation to clinical practice. Emerging data will help in improving guidance, and a more evidence-based approach of managing chromosomal mosaicism.

STUDY FUNDING/COMPETING INTEREST(S)

The WG received technical support from ESHRE. M.D.R. participated in the EQA special advisory group, outside the submitted work, and is the chair of the PGT WG of the Belgian society for human genetics. D.W. declared receiving salary from Juno Genetics, UK. A.C. is an employee of Igenomix, Italy and C.R. is an employee of Igenomix, Spain. C.S. received a research grant from FWO, Belgium, not related to the submitted work. I.S. declared being a Co-founder of IVFvision Ltd, UK. J.R.V. declared patents related to ‘Methods for haplotyping single-cells’ and ‘Haplotyping and copy number typing using polymorphic variant allelic frequencies’, and being a board member of Preimplantation Genetic Diagnosis International Society (PGDIS) and International Society for Prenatal Diagnosis (ISPD). K.S. reported being Chair-elect of ESHRE. The other authors had nothing to disclose.

DISCLAIMER

This Good Practice Recommendations (GPR) document represents the views of ESHRE, which are the result of consensus between the relevant ESHRE stakeholders and are based on the scientific evidence available at the time of preparation. 

ESHRE GPRs should be used for information and educational purposes. They should not be interpreted as setting a standard of care or be deemed inclusive of all proper methods of care, or be exclusive of other methods of care reasonably directed to obtaining the same results. They do not replace the need for application of clinical judgement to each individual presentation, or variations based on locality and facility type. 

Furthermore, ESHRE GPRs do not constitute or imply the endorsement, or favouring, of any of the included technologies by ESHRE. 

On the reproductive capabilities of aneuploid human preimplantation embryos

In IVF cycles, the application of aneuploidy testing at the blastocyst stage is quickly growing, and the latest reports estimate almost half of cycles in the US undergo preimplantation genetic testing for aneuploidies (PGT-A). Following PGT-A cycles, understanding the predictive value of an aneuploidy result is paramount for making informed decisions about the embryo's fate and utilization. Compelling evidence from non-selection trials strongly supports that embryos diagnosed with a uniform whole-chromosome aneuploidy very rarely result in the live birth of a healthy baby, while their transfer exposes women to significant risks of miscarriage and chromosomally abnormal pregnancy. On the other hand, embryos displaying low range mosaicism for whole chromosomes have shown reproductive capabilities somewhat equivalent to uniformly euploid embryos, and they have comparable clinical outcomes and gestational risks. Therefore, given their clearly distinct biological origin and clinical consequences, careful differentiation between uniform and mosaic aneuploidy is critical in both the clinical setting when counseling individuals and in the research setting when presenting aneuploidy studies in human embryology. Here, we focus on the evidence gathered so far on PGT-A diagnostic predictive values and reproductive outcomes observed across the broad spectrum of whole-chromosome aneuploidies detected at the blastocyst stage to obtain evidence-based conclusions on the clinical management of aneuploid embryos in the quickly growing PGT-A clinical setting.

Development of an artificial intelligence model for predicting the likelihood of human embryo euploidy based on blastocyst images from multiple imaging systems during IVF

STUDY QUESTION

Can an artificial intelligence (AI) model predict human embryo ploidy status using static images captured by optical light microscopy?

SUMMARY ANSWER

Results demonstrated predictive accuracy for embryo euploidy and showed a significant correlation between AI score and euploidy rate, based on assessment of images of blastocysts at Day 5 after IVF.

WHAT IS KNOWN ALREADY

Euploid embryos displaying the normal human chromosomal complement of 46 chromosomes are preferentially selected for transfer over aneuploid embryos (abnormal complement), as they are associated with improved clinical outcomes. Currently, evaluation of embryo genetic status is most commonly performed by preimplantation genetic testing for aneuploidy (PGT-A), which involves embryo biopsy and genetic testing. The potential for embryo damage during biopsy, and the non-uniform nature of aneuploid cells in mosaic embryos, has prompted investigation of additional, non-invasive, whole embryo methods for evaluation of embryo genetic status.

STUDY DESIGN, SIZE, DURATION

A total of 15 192 blastocyst-stage embryo images with associated clinical outcomes were provided by 10 different IVF clinics in the USA, India, Spain and Malaysia. The majority of data were retrospective, with two additional prospectively collected blind datasets provided by IVF clinics using the genetics AI model in clinical practice. Of these images, a total of 5050 images of embryos on Day 5 of in vitro culture were used for the development of the AI model. These Day 5 images were provided for 2438 consecutively treated women who had undergone IVF procedures in the USA between 2011 and 2020. The remaining images were used for evaluation of performance in different settings, or otherwise excluded for not matching the inclusion criteria.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The genetics AI model was trained using static 2-dimensional optical light microscope images of Day 5 blastocysts with linked genetic metadata obtained from PGT-A. The endpoint was ploidy status (euploid or aneuploid) based on PGT-A results. Predictive accuracy was determined by evaluating sensitivity (correct prediction of euploid), specificity (correct prediction of aneuploid) and overall accuracy. The Matthew correlation coefficient and receiver-operating characteristic curves and precision-recall curves (including AUC values), were also determined. Performance was also evaluated using correlation analyses and simulated cohort studies to evaluate ranking ability for euploid enrichment.

MAIN RESULTS AND THE ROLE OF CHANCE

Overall accuracy for the prediction of euploidy on a blind test dataset was 65.3%, with a sensitivity of 74.6%. When the blind test dataset was cleansed of poor quality and mislabeled images, overall accuracy increased to 77.4%. This performance may be relevant to clinical situations where confounding factors, such as variability in PGT-A testing, have been accounted for. There was a significant positive correlation between AI score and the proportion of euploid embryos, with very high scoring embryos (9.0-10.0) twice as likely to be euploid than the lowest-scoring embryos (0.0-2.4). When using the genetics AI model to rank embryos in a cohort, the probability of the top-ranked embryo being euploid was 82.4%, which was 26.4% more effective than using random ranking, and ∼13-19% more effective than using the Gardner score. The probability increased to 97.0% when considering the likelihood of one of the top two ranked embryos being euploid, and the probability of both top two ranked embryos being euploid was 66.4%. Additional analyses showed that the AI model generalized well to different patient demographics and could also be used for the evaluation of Day 6 embryos and for images taken using multiple time-lapse systems. Results suggested that the AI model could potentially be used to differentiate mosaic embryos based on the level of mosaicism.

LIMITATIONS, REASONS FOR CAUTION

While the current investigation was performed using both retrospectively and prospectively collected data, it will be important to continue to evaluate real-world use of the genetics AI model. The endpoint described was euploidy based on the clinical outcome of PGT-A results only, so predictive accuracy for genetic status in utero or at birth was not evaluated. Rebiopsy studies of embryos using a range of PGT-A methods indicated a degree of variability in PGT-A results, which must be considered when interpreting the performance of the AI model.

WIDER IMPLICATIONS OF THE FINDINGS

These findings collectively support the use of this genetics AI model for the evaluation of embryo ploidy status in a clinical setting. Results can be used to aid in prioritizing and enriching for embryos that are likely to be euploid for multiple clinical purposes, including selection for transfer in the absence of alternative genetic testing methods, selection for cryopreservation for future use or selection for further confirmatory PGT-A testing, as required.

STUDY FUNDING/COMPETING INTEREST(S)

Life Whisperer Diagnostics is a wholly owned subsidiary of the parent company, Presagen Holdings Pty Ltd. Funding for the study was provided by Presagen with grant funding received from the South Australian Government: Research, Commercialisation, and Startup Fund (RCSF). 'In kind' support and embryology expertise to guide algorithm development were provided by Ovation Fertility. 'In kind' support in terms of computational resources provided through the Amazon Web Services (AWS) Activate Program. J.M.M.H., D.P. and M.P. are co-owners of Life Whisperer and Presagen. S.M.D., M.A.D. and T.V.N. are employees or former employees of Life Whisperer. S.M.D, J.M.M.H, M.A.D, T.V.N., D.P. and M.P. are listed as inventors of patents relating to this work, and also have stock options in the parent company Presagen. M.V. sits on the advisory board for the global distributor of the technology described in this study and also received support for attending meetings.

TRIAL REGISTRATION NUMBER

N/A.

Clinical re-biopsy of segmental gains-the primary source of preimplantation genetic testing false positives

PURPOSE

Does re-biopsy of blastocysts classified as abnormal (ABN) due to segmental aneuploidy (SA) have clinical utility?

METHODS

The live birth (LB) outcomes of mosaic SAs, compared to other categories, were determined after transfer of 3084 PGT-A tested blastocysts. An initial 12-month trial thawed 111 blastocysts classified as ABN due to a SA for clinical re-biopsy, with an additional 58 from a subsequent 16-month revised protocol. Where re-biopsy failed to corroborate the original classification, blastocysts were reported as mosaic and suitable for clinical use.

RESULTS

Segmental mosaics had a LB rate (54.1%) which was indistinguishable from that of euploid (53.7%). Numeric mosaics had statistically significant (P < 0.05) reduced LB rates compared to euploid, with high-level numerics (19.2%) also exhibiting a significant reduction compared to low level (42.3%). Of the initial 111 blastocysts with SAs, 85 could be re-biopsied. Segmental gains became suitable for re-biopsy at a high rate (90.9%), with 84.2% (16/19) of these reclassified as mosaic. Only 73.0% of deletions and complex changes were suitable for re-biopsy, of which 73.0% (46/63) were confirmed ABN. The subsequent 16-month period primarily focused on gains, confirming the high rate at which they can be reclassified as clinically useable.

CONCLUSIONS

Blastocysts harboring mosaic segmental duplications, rather than SAs in general, are the primary source of false-positive PGT-A results and represent a category with a LB rate similar to that of euploid. A high degree of confidence in the reliability of PGT-A results can be maintained by performing confirmatory clinical TE biopsies.

The effects of differences in trophectoderm biopsy techniques and the number of cells collected for biopsy on next‐generation sequencing results

Purpose

To examine how differences in trophectoderm biopsy techniques affect the frequency of mosaic embryos and sequencing results.

Methods

We examined differences in next‐generation sequencing (NGS) analysis results among operators or according to biopsy technique. Additionally, we determined the cut‐off for the number of collected cells to predict the occurrence of mosaicism. We collected cells according to the cut‐off value and examined whether there was a difference in the NGS analysis results between the pulling and flicking methods.

Results

There was no difference in the NGS analysis results among the operators. Regarding re‐biopsy, changes in the mosaic were observed in all specimens. The cut‐off value for the number of collected cells was five, and when more than five cells were collected, there was no difference in the NGS analysis results between the two methods.

Conclusions

We demonstrated that if trophectoderm biopsy techniques and NGS are stable, the cell collection location has a greater effect on NGS results than the biopsy technique.

Comparison of chromosomal status in reserved multiple displacement amplification products of embryos that resulted in miscarriages or live births: a blinded, nonselection case-control study

Objective

To analyze chromosomal status in reserved multiple displacement amplification (MDA) products of embryos that result in miscarriages or live births.

Methods

Patients who underwent preimplantation genetic testing for monogenic disorders (PGT-Ms) without aneuploidy screening were included. The case group included 28 cycles that resulted in miscarriages. Controls included 56 cycles with live births. Comprehensive chromosomal screening (CCS) using next-generation sequencing (NGS) was performed on reserved MDA products from previous blastocyst trophectoderm biopsies. The incidence and type of chromosomal abnormalities in embryos resulting in miscarriages or live births were analyzed.

Results

Of 28 embryos resulting in miscarriages in the case group, the rate of chromosomal abnormalities was 53.6%, which was significantly greater than 14.3% for those resulting in live births in control group (P < 0.001). Whole-chromosome aneuploidy was not found in the control group but was noted in 25.0% of embryos in the case group. Although the rates of segmental abnormality and mosaicism were also greater in the case group, no significant differences were detected. One chaotic embryo in the control group progressed to live birth.

Conclusion

Chromosomal abnormalities were the main reason leading to early pregnancy loss. However, abnormalities, such as segmental aneuploidy and mosaicism, should be managed cautiously, considering their undermined reproductive potential.

The concordance rates of an initial trophectoderm biopsy with the rest of the embryo using PGTseq, a targeted next-generation sequencing platform for preimplantation genetic testing-aneuploidy

OBJECTIVE

To determine how often the results of a single trophectoderm (TE) biopsy tested by PGTseq, a targeted next-generation sequencing preimplantation genetic testing for aneuploidy technology, reflect the biology of the rest of the embryo.

DESIGN

Blinded prospective cohort study.

SETTING

University-affiliated private practice.

PATIENT(S)

A total of 300 blastocysts were donated; 113 of these embryos were euploid; 163 embryos possessed at least one whole chromosome aneuploidy; and 24 embryos were negative for whole chromosome aneuploidy but possessed at least one secondary finding on initial TE biopsy.

INTERVENTION(S)

All blastocysts underwent rebiopsy and preimplantation genetic testing for aneuploidy on the PGTseq platform.

MAIN OUTCOME MEASURE(S)

Partial concordance rate per embryo, total concordance rate per embryo, and total concordance rate per chromosomal event.

RESULT(S)

An initial TE biopsy result of euploidy or whole chromosome aneuploidy was reconfirmed in >99% of rebiopsied samples, affirming that meiotic errors are manifested in almost the entire embryo. In contrast, results of whole chromosome or segmental mosaicism were confirmed in 15%-18% of subsequent rebiopsies, suggesting that mitotic events are only sporadically seen throughout the embryo. Segmental aneuploidy was confirmed in 56.6% of rebiopsied samples, identifying a mixed meiotic and mitotic etiology for such abnormalities.

CONCLUSION(S)

A euploid or aneuploid result on the PGTseq platform is highly concordant with the rest of the embryo's ploidy status. The rarer confirmation of whole chromosome mosaic and segmental mosaic results suggest that these mosaics are suitable for embryo transfer. Segmental aneuploidy, with higher concordance rates throughout the embryo, may represent a different biologic etiology compared to mosaic embryos.

From contemplation to classification of chromosomal mosaicism in human preimplantation embryos

Chromosomal mosaicism is a hallmark of early human embryo development. The last decade yielded an enormous amount of information about diversity and prevalence of mosaicism in preimplantation embryos due to progress in preimplantation genetic testing of aneuploidies (PGT-A) based exclusively on molecular karyotyping of trophectoderm biopsy. However, the inner cell mass karyotype is still missing for mosaic embryos affecting the success rate of assisted reproductive medicine. Here, a classification model of chromosomal mosaicism is proposed based on the analysis of the primary zygote karyotype, the timing and types of primary and secondary chromosome segregation errors, and the distribution of mosaic cell clones between different embryonic and extraembryonic compartments of the blastocyst. Five basic principles for mosaicism analysis are introduced, namely, the estimation of the primary zygote karyotype, the investigation of additional sample point, the requirement of the second time point analysis, the delineating of reciprocity of chromosome segregation, and comprehensive chromosome screening at the single-cell level. The suggested model allows the prediction of the inner cell mass karyotype of the blastocyst and its developmental potential based on information from trophectoderm biopsy and non-invasive PGT-A using blastocoele fluid sample or spent culture medium as additional sample and time points for analysis and considering the reciprocity as a basic process in chromosome segregation errors between daughter cells in postzygotic cell divisions.

Evidence-based management of preimplantation chromosomal mosaicism: lessons from the clinic

Mosaic results obtained through preimplantation genetic testing for aneuploidy pose ongoing challenges to clinical practice. Thorough genetic counseling for patients considering mosaic embryo transfer is consistently recommended by many best-practice statements, and providers are charged with the task of assessing and explaining potential prenatal, neonatal, and long-term risks. However, an increasing amount of outcome data from transferred embryos with mosaic results do not show any evidence of increased risk to ongoing pregnancies or newborns. This article examines how to reconcile these data with the current practices for patient education about preimplantation genetic testing for aneuploidy and mosaic embryo risk assessment, through an evidence-based lens.

Experience analysing over 190,000 embryo trophectoderm biopsies using a novel FAST-SeqS preimplantation genetic testing assay

RESEARCH QUESTION

Is FAST-SeqS an accurate methodology for preimplantation genetic testing for whole-chromosome aneuploidy (PGT-A)? What additional types of chromosomal abnormalities can be assessed? What are the observed aneuploidy rates in a large clinical cohort?

DESIGN

FAST-SeqS, a next-generation sequencing (NGS)-based assay amplifying genome-wide LINE1 repetitive sequences, was validated using reference samples. Sensitivity and specificity were calculated. Clinically derived trophectoderm biopsies submitted for PGT-A were assessed, and aneuploidy and mosaicism rates among biopsies were determined. Clinician-provided outcome rates were calculated.

RESULTS

Sensitivity and specificity were over 95% for all aneuploidy types tested in the validation. Comparison of FAST-SeqS with VeriSeq showed high concordance (98.5%). Among embryos with actionable results (n = 182,827), 46.2% were aneuploid. Whole-chromosome aneuploidies were most observed (72.9% without or 8.7% with a segmental aneuploidy), with rates increasing with egg age; segmental aneuploidy rates did not. Segmental aneuploidy (n = 20,557) was observed on all chromosomes (most commonly deletions), with frequencies associated with chromosome length. Mosaic-only abnormalities constituted 10.1% (n = 3862/38145) of samples. Abnormal ploidy constituted 1.8% (n = 2370/128,991) of samples, triploidy being the most common (73.6%). Across 3297 frozen embryo transfers, the mean clinical pregnancy rate was 62% (range 38-80%); the mean combined ongoing pregnancy and live birth rate was 57% (range 38-72%).

CONCLUSION

FAST-SeqS is a clinically reliable and scalable method for PGT-A, is comparable to whole-genome amplification-based platforms, and detects additional information related to ploidy using SNP analysis. Results suggest ongoing benefit of PGT-A using FAST-SeqS, consistent with other platforms.

The true incidence of chromosomal mosaicism after preimplantation genetic testing is much lower than that indicated by trophectoderm biopsy

STUDY QUESTION

What is the true incidence of chromosomal mosaicism in embryos analyzed by preimplantation genetic testing (PGT).

SUMMARY ANSWER

The true incidence of chromosomal mosaicism is much lower than we usually surmise.

WHAT IS KNOWN ALREADY

In recent years, contemporary methods for chromosome analysis, along with the biopsy of more than one cell, have given rise to an increased rate of chromosomal mosaicism detection after preimplantation genetic testing for aneuploidy. However, the exorbitant incidence of mosaicism represents a dilemma and imposes restrictions on the application of PGT treatment. Concern has been raised about the possibility that the incidence of chromosomal mosaicism is overestimated and quite a few of the results are false-positive errors. However, studies verifying the diagnosis of chromosomal mosaicism and assessing the true incidence of chromosomal mosaicism are limited.

STUDY DESIGN, SIZE, DURATION

A total of 1719 blastocysts from 380 patients who underwent PGT treatment were retrospectively analyzed to evaluate the typical incidence of mosaicism. Then 101 embryos donated by 70 couples were re-biopsied and dissected into three portions if available: trophectoderm (TE), inner cell mass (ICM), and the remaining portions. All the portions were tested using next-generation sequencing (NGS), and the results were compared to the original diagnosis.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The setting for this study was a university-affiliated center with an in-house PGT laboratory. All samples were amplified with multiple annealing and looping-based amplification cycles (MALBACs) and the NGS was carried out on a Life Technologies Ion Proton platform.

MAIN RESULTS AND THE ROLE OF CHANCE

A clinical TE biopsy revealed an incidence of 11.9% for diploid-aneuploid mosaicism (DAM), 17.3% for aneuploid mosaicism (AM) and 29.1% in total. After rebiopsy, 94.1% whole-chromosome aneuploidies and 82.8% segmental-chromosome aneuploidies were confirmed in the embryos. As for the mosaic errors, only 32 (31.7%) out of 101 embryos presented with uniform chromosomal aberrations in agreement with the original biopsy results, 15 (14.8%) embryos presented with de novo chromosomal aberrations, and 54 (53.5%) embryos showed a euploid profile in all portions. Among the 32 uniform embryos, the true mosaicism was confirmed in only 4 cases, where a reciprocal chromosomal aberration was identified; 14 embryos presented with identical mosaicism, providing the moderate evidence for true mosaicism; and 14 embryos displayed uniform full aneuploidies in all portions of embryo, revealing a high-grade mosaicism or a false-negative diagnosis. Logistical regression analysis revealed that the concordance rate with ICM was associated with the type and level of mosaicism. The concordance rate of segmental-chromosome mosaicism was significantly lower than whole-chromosome mosaicism (adjusted Odds Ratio (aOR): 5.137 (1.061, 24.876), P = 0.042) and compared to DAM, the concordance rate of AM was significantly higher (aOR: 6.546 (1.354, 31.655), P = 0.019). The concordance rate also increased with increasing levels of mosaicism (P < 0.001).

LIMITATIONS, REASONS FOR CAUTION

This study was limited by a small sample size and the use of a single whole-genome amplification (WGA) method and NGS platform. These findings are only applicable to samples subjected to MALBAC amplification and Ion Proton platform, and studies involving larger sample sizes and multiple WGA methods and NGS platforms are required to prove our findings.

WIDER IMPLICATIONS OF THE FINDINGS

TE biopsy is reliable to detect whole-chromosome aneuploidies, but the ability to diagnose mosaicism is doubtful. More attention should be paid to false-positive and false-negative errors in NGS-based PGT, especially for laboratories using less stringent criteria for mosaicism classification (i.e. 20-80%), which might be subject to a much higher false-positive mosaicism rate in the practice.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by grants from the National Key R&D Program of China (No. 2016YFC1000206-5) and the National Natural Science Foundation of China (No. 81701509).

TRIAL REGISTRATION NUMBER

N/A.

Rescuing monopronucleated-derived human blastocysts: a model to study chromosomal topography and fingerprinting

OBJECTIVE

To quantify the percentage of monopronuclear-derived blastocysts (MNBs) that are potentially useful for reproductive purposes using classic and state-of-the-art chromosome analysis approaches, and to study chromosomal distribution in the inner cell mass (ICM) and trophectoderm (TE) for intertissue/intratissue concordance comparison.

DESIGN

Prospective experimental study.

SETTING

Single-center in vitro fertilization clinic and reproductive genetics laboratory.

PATIENT(S)

A total of 1,128 monopronuclear zygotes were obtained between June 2016 and December 2018.

INTERVENTION(S)

MNBs were whole-fixed or biopsied to obtain a portion of ICM and 2 TE portions (TE1 and TE2) and were subsequently analyzed by fluorescence in situ hybridization, new whole-genome sequencing, and fingerprinting by single-nucleotide polymorphism array-based techniques (a-SNP).

MAIN OUTCOME MEASURE(S)

We assessed MNB rate, ploidy rate, and chromosomal constitution by new whole-genome sequencing, and parental composition by comparative a-SNP, performed in a "trio"-format (embryo/parents). The 24-chromosome distribution was compared between the TE and the ICM and within the TE.

RESULT(S)

A total of 18.4% of monopronuclear zygotes progressed to blastocysts; 77.6% of MNBs were diploid; 20% of MNBs were male and euploid, which might be reproductively useful. Seventy-five percent of MNBs were biparental and half of them were euploid, indicating that 40% might be reproductively useful. Intratissue concordance (TE1/TE2) was established for 93.3% and 73.3% for chromosome matching. Intertissue concordance (TE/ICM) was established for 78.8%, but 57.6% for chromosome matching. When segmental aneuploidy was not considered, intratissue concordance and chromosome matching increased to 100% and 80%, respectively, and intertissue concordance and chromosome matching increased to 84.8% and 75.8%, respectively.

CONCLUSION(S)

The a-SNP-trio strategy provides information about ploidy, euploidy, and parental origin in a single biopsy. This approach enabled us to identify 40% of MNBs with reproductive potential, which can have a significant effect in the clinical setting. Additionally, segmental aneuploidy is relevant for mismatched preimplantation genetic testing of aneuploidies, both within and between MNB tissues. Repeat biopsy might clarify whether segmental aneuploidy is a prone genetic character.

Pregnancy and Neonatal Outcomes after Transfer of Mosaic Embryos: A Review

Preimplantation genetic testing for aneuploidy (PGT-A) seeks to identify embryos with a normal chromosome complement during in vitro fertilization (IVF). Transfer of one euploid embryo at a time maximizes the chance of implantation while minimizing the risk of multiple pregnancy. The emergence of new technologies including next generation sequencing (NGS) has led to increased diagnosis of embryonic mosaicism, suggesting the presence of karyotypically distinct cells within a single trophectoderm (TE). Clinical implications of embryonic mosaicism are important in both naturally conceived and IVF pregnancies. Although information regarding outcomes after mosaic embryo transfer (MET) is limited, more than 100 live births have now been documented with rather reassuring outcomes with no abnormal phenotype. Here, we aim to provide a summary of recent data regarding clinical and neonatal outcomes after transfer of mosaic embryos in IVF/PGT-A cycles.

Chromosomal mosaicism: Origins and clinical implications in preimplantation and prenatal diagnosis

The diagnosis of chromosomal mosaicism in the preimplantation and prenatal stage is fraught with uncertainty and multiple factors need to be considered in order to gauge the likely impact. The clinical effects of chromosomal mosaicism are directly linked to the type of the imbalance (size, gene content, and copy number), the timing of the initial event leading to mosaicism during embryogenesis/fetal development, the distribution of the abnormal cells throughout the various tissues within the body as well as the ratio of normal/abnormal cells within each of those tissues. Additional factors such as assay noise and culture artifacts also have an impact on the significance and management of mosaic cases. Genetic counseling is an important part of educating patients about the likelihood of having a liveborn with a chromosome abnormality and these risks differ according to the time of ascertainment and the tissue where the mosaic cells were initially discovered. Each situation needs to be assessed on a case-by-case basis and counseled accordingly. This review will discuss the clinical impact of finding mosaicism through: embryo biopsy, chorionic villus sampling, amniocentesis, and noninvasive prenatal testing using cell-free DNA.

Using outcome data from one thousand mosaic embryo transfers to formulate an embryo ranking system for clinical use

OBJECTIVE

To study how the attributes of mosaicism identified during preimplantation genetic testing for aneuploidy relate to clinical outcomes, in order to formulate a ranking system of mosaic embryos for intrauterine transfer.

DESIGN

Compiled analysis.

SETTING

Multi-center.

PATIENT(S)

A total of 5,561 euploid blastocysts and 1,000 mosaic blastocysts used in clinical transfers in patients undergoing fertility treatment.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Implantation (gestational sac), ongoing pregnancy, birth, and spontaneous abortion (miscarriage before 20 weeks of gestation).

RESULT(S)

The euploid group had significantly more favorable rates of implantation and ongoing pregnancy/birth (OP/B) compared with the combined mosaic group or the mosaic group affecting only whole chromosomes (implantation: 57.2% vs. 46.5% vs. 41.8%; OP/B: 52.3% vs. 37.0% vs. 31.3%), as well as lower likelihood of spontaneous abortion (8.6% vs. 20.4% vs. 25%). Whole-chromosome mosaic embryos with level (percent aneuploid cells) <50% had significantly more favorable outcomes than the ≥50% group (implantation: 44.5% vs. 30.4%; OP/B: 36.1% vs. 19.3%). Mosaic type (nature of the aneuploidy implicated in mosaicism) affected outcomes, with a significant correlation between number of affected chromosomes and unfavorable outcomes. This ranged from mosaicism involving segmental abnormalities to complex aneuploidies affecting three or more chromosomes (implantation: 51.6% vs. 30.4%; OP/B: 43.1% vs. 20.8%). Combining mosaic level, type, and embryo morphology revealed the order of subcategories regarding likelihood of positive outcome.

CONCLUSION(S)

This compiled analysis revealed traits of mosaicism identified with preimplantation genetic testing for aneuploidy that affected outcomes in a statistically significant manner, enabling the formulation of an evidence-based prioritization scheme for mosaic embryos in the clinic.

Validation of preimplantation genetic tests for aneuploidy (PGT-A) with DNA from spent culture media (SCM): concordance assessment and implication

BACKGROUND

Spent culture medium (SCM) as a source of DNA for preimplantation genetic tests aneuploidy (PGT-A) has been widely discussed.

METHODS

Seventy-five blastocysts that were donated for research provided a unique possibility in which multiple specimens, including trophectoderm (TE) biopsy, SCM, and paired corresponding whole blastocyst (WB) specimens from the same blastocyst source, could be utilized for the purpose of this preclinical validation.

RESULTS

To conduct a validation ploidy concordance assessment, we evaluated the full chromosomal concordance rates between SCM and WB (SCM-to-WB), and between TE and WB (TE-to-WB) as well as sensitivity, specificity and overall diagnostic accuracy. 78.67% (59/75) of NGS results in the SCM group were interpretable, a significantly lower percentage than their corresponding TE and WB groups. This discrepancy manifests itself in intrinsically low quantity and poor integrity DNA from SCM. Subsequently, remarkable differences in full concordance rates (including mosaicism, and segmental aneuploidies) are seen as follows: 32.2% (SCM-to-WB, 19/59) and 69.33% (TE-to-WB, 52/75), (p < 0.001). In such cases, full concordance rates were 27.27% (15/55) in SCM-to-WB, and, 76% (57/75) in TE-to-WB (p < 0.001). Collectively, the NGS data from SCM also translated into lower sensitivities, Positive Predictive Value (PPV), Negative Predictive Value (NPV), overall diagnostic accuracies, and higher Negative Likelihood Ratio (NLR).

CONCLUSIONS

Our study reveals that DNA is detectable in the majority of SCM samples. Individual chromosomal aberration, such as segmental aneuploidy and mosaicism, can be quantitatively and qualitatively measured. However, TE still provides a more accurate and reliable high-throughput methodology for PGT-A. Meanwhile, cell-free DNA in SCM reporting lacks uniform diagnostic interpretations. Considering that this test is meant to determine which embryos are relegated to be discarded, PGT-A with cell-free DNA in SCM should not be permitted to be applied in routine clinical settings for diagnosis purpose.

Preimplantation genetic testing for aneuploidy: A review of published blastocyst reanalysis concordance data

Preimplantation genetic testing for aneuploidy (PGT‐A) reduces miscarriage risk, increases the success of IVF, shortens time to pregnancy, and reduces multiple gestation rates without compromising outcomes. The progression of PGT‐A has included common application of next‐generation sequencing (NGS) from single nucleotide polymorphism microarray, quantitative real‐time PCR, and array comparative hybridization platforms of analysis. Additional putative advances in PGT‐A capability include classifying embryos as mosaic and predicting the presence of segmental imbalance. A critical component in the process of technical validation of these advancements involves evaluation of concordance between reanalysis results and initial testing results. While many independent studies have investigated the concordance of results obtained from the remaining embryo with the original PGT‐A diagnosis, compilation and systematic analysis of published data has not been performed. Here, we review results from 26 primary research articles describing concordance in 1271 human blastocysts from 2260 pairwise comparisons. Results illustrate significantly higher discordance from PGT‐A methods which utilize NGS and include prediction of mosaicism or segmental imbalance. These results suggest caution when considering new iterations PGT‐A.

Copy number analysis of meiotic and postzygotic mitotic aneuploidies in trophectoderm cells biopsied at the blastocyst stage and arrested embryos

Preimplantation genetic testing for aneuploidy (PGT-A) by copy number analysis is now widely used to select euploid embryos for transfer. Whole or partial chromosome aneuploidy can arise in meiosis, predominantly female meiosis, or in the postzygotic, mitotic divisions during cleavage and blastocyst formation, resulting in chromosome mosaicism. Meiotic aneuploidies are almost always lethal, however, the clinical significance of mitotic aneuploidies detected by PGT-A is not fully understood and healthy live births have been reported following transfer of mosaic embryos. Here, we used single nucleotide polymorphism genotyping of both polar bodies and embryo samples to identify meiotic aneuploidies and compared copy number changes for meiotic and presumed mitotic aneuploidies in trophectoderm cells biopsied at the blastocyst stage and arrested embryos. PGT-A detected corresponding full copy number changes (≥70%) for 36/37 (97%) maternal meiotic aneuploidies. The number of presumed mitotic copy number changes detected exceeded those of meiotic origin. Although mainly in the mosaic range, some of these mitotic aneuploidies had copy number changes ≥70% and would have been identified as full aneuploidies. Interestingly, many arrested embryos had multiple mitotic aneuploidies across a broad range of copy number changes, which may have arisen through tripolar spindle and other mitotic abnormalities.

Preimplantation Genetic Testing for Chromosomal Abnormalities: Aneuploidy, Mosaicism, and Structural Rearrangements

There is a high incidence of chromosomal abnormalities in early human embryos, whether they are generated by natural conception or by assisted reproductive technologies (ART). Cells with chromosomal copy number deviations or chromosome structural rearrangements can compromise the viability of embryos; much of the naturally low human fecundity as well as low success rates of ART can be ascribed to these cytogenetic defects. Chromosomal anomalies are also responsible for a large proportion of miscarriages and congenital disorders. There is therefore tremendous value in methods that identify embryos containing chromosomal abnormalities before intrauterine transfer to a patient being treated for infertility—the goal being the exclusion of affected embryos in order to improve clinical outcomes. This is the rationale behind preimplantation genetic testing for aneuploidy (PGT-A) and structural rearrangements (-SR). Contemporary methods are capable of much more than detecting whole chromosome abnormalities (e.g., monosomy/trisomy). Technical enhancements and increased resolution and sensitivity permit the identification of chromosomal mosaicism (embryos containing a mix of normal and abnormal cells), as well as the detection of sub-chromosomal abnormalities such as segmental deletions and duplications. Earlier approaches to screening for chromosomal abnormalities yielded a binary result of normal versus abnormal, but the new refinements in the system call for new categories, each with specific clinical outcomes and nuances for clinical management. This review intends to give an overview of PGT-A and -SR, emphasizing recent advances and areas of active development.