Mosaicism between trophectoderm and inner cell mass

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.

Mechanism of chromosomal mosaicism in preimplantation embryos and its effect on embryo development

Aneuploidy is one of the main causes of miscarriage and in vitro fertilization failure. Mitotic abnormalities in preimplantation embryos are the main cause of mosaicism, which may be influenced by several endogenous factors such as relaxation of cell cycle control mechanisms, defects in chromosome cohesion, centrosome aberrations and abnormal spindle assembly, and DNA replication stress. In addition, incomplete trisomy rescue is a rare cause of mosaicism. However, there may be a self-correcting mechanism in mosaic embryos, which allows some mosaicisms to potentially develop into normal embryos. At present, it is difficult to accurately diagnose mosaicism using preimplantation genetic testing for aneuploidy. Therefore, in clinical practice, embryos diagnosed as mosaic should be considered comprehensively based on the specific situation of the patient.

Evolution of Minimally Invasive and Non-Invasive Preimplantation Genetic Testing: An Overview

Preimplantation genetic testing (PGT) has become a common supplementary diagnοstic/testing tοol for in vitro fertilization (ΙVF) cycles due to a significant increase in cases of PGT fοr mοnogenic cοnditions (ΡGT-M) and de novο aneuplοidies (ΡGT-A) over the last ten years. This tendency is mostly attributable to the advancement and application of novel cytogenetic and molecular techniques in clinical practice that are capable of providing an efficient evaluation of the embryonic chromosomal complement and leading to better IVF/ICSI results. Although PGT is widely used, it requires invasive biopsy of the blastocyst, which may harm the embryo. Non-invasive approaches, like cell-free DNA (cfDNA) testing, have lower risks but have drawbacks in consistency and sensitivity. This review discusses new developments and opportunities in the field of preimplantation genetic testing, enhancing the overall effectiveness and accessibility of preimplantation testing in the framework of developments in genomic sequencing, bioinformatics, and the integration of artificial intelligence in the interpretation of genetic data.

To transfer or not to transfer: the dilemma of mosaic embryos - a narrative review

A frequent finding after preimplantation genetic diagnostic testing for aneuploidies using next-generation sequencing is an embryo that is putatively mosaic. The prevalence of this outcome remains unclear and varies with technical and external factors. Mosaic embryos can be classified by the percentage of cells affected, type of chromosome involvement (whole or segmental), number of affected chromosomes or affected cell type (inner mass cell, trophectoderm or both). The origin of mosaicism seems to be intrinsic as a post-zygotic mitotic error, but some external factors can play a role. As experience has increased with the transfer of mosaic embryos, clinical practice has gradually become more flexible in recent years. Nevertheless, clinical results show lower implantation, pregnancy and clinical pregnancy rates and higher miscarriage rates with mosaic embryo transfer when compared with the transfer of euploid embryos. Prenatal diagnosis is highly recommended after the transfer of mosaic embryos. This narrative review is intended to serve as reference material for practitioners in reproductive medicine who must manage a mosaic embryo result after preimplantation genetic testing for aneuploidies.

Single-cell DNA sequencing reveals a high incidence of chromosomal abnormalities in human blastocysts

Aneuploidy, a deviation from the normal chromosome copy number, is common in human embryos and is considered a primary cause of implantation failure and early pregnancy loss. Meiotic errors lead to uniformly abnormal karyotypes, while mitotic errors lead to chromosomal mosaicism: the presence of cells with at least 2 different karyotypes within an embryo. Knowledge about mosaicism in blastocysts mainly derives from bulk DNA sequencing (DNA-Seq) of multicellular trophectoderm (TE) and/or inner cell mass (ICM) samples. However, this can only detect an average net gain or loss of DNA above a detection threshold of 20%-30%. To accurately assess mosaicism, we separated the TE and ICM of 55 good-quality surplus blastocysts and successfully applied single-cell whole-genome sequencing (scKaryo-Seq) on 1,057 cells. Mosaicism involving numerical and structural chromosome abnormalities was detected in 82% of the embryos, in which most abnormalities affected less than 20% of the cells. Structural abnormalities, potentially caused by replication stress and DNA damage, were observed in 69% of the embryos. In conclusion, our findings indicated that mosaicism was prevalent in good-quality blastocysts, whereas these blastocysts would likely be identified as normal with current bulk DNA-Seq techniques used for preimplantation genetic testing for aneuploidy.

Embryo drop-out rates in preimplantation genetic testing for aneuploidy (PGT-A): a retrospective data analysis from the DoLoRes study

PURPOSE

To evaluate the decline in transferable embryos in preimplantation genetic testing for aneuploidy (PGT-A) cycles due to (a) non-biopsable blastocyst quality, (b) failure of genetic analysis, (c) diagnosis of uniform numerical or structural chromosomal aberrations, and/or (d) chromosomal aberrations in mosaic constitution.

METHODS

This retrospective multicenter study comprised outcomes of 1562 blastocysts originating from 363 controlled ovarian stimulation cycles, respectively, 226 IVF couples in the period between January 2016 and December 2018. Inclusion criteria were PGT-A cycles with trophectoderm biopsy (TB) and next generation sequencing (NGS).

RESULTS

Out of 1562 blastocysts, 25.8% were lost due to non-biopsable and/or non-freezable embryo quality. In 10.3% of all biopsied blastocysts, genetic analysis failed. After exclusion of embryos with uniform or chromosomal aberrations in mosaic, only 18.1% of those originally yielded remained as diagnosed euploid embryos suitable for transfer. This translates into 50.4% of patients and 57.6% of stimulated cycles with no euploid embryo left for transfer. The risk that no transfer can take place rose significantly with a lower number of oocytes and with increasing maternal age. The chance for at least one euploid blastocyst/cycle in advanced maternal age (AMA)-patients was 33.3% compared to 52.1% in recurrent miscarriage (RM), 59.8% in recurrent implantation failure (RIF), and 60.0% in severe male factor (SMF).

CONCLUSIONS

The present study demonstrates that PGT-A is accompanied by high embryo drop-out rates. IVF-practitioners should be aware that their patients run a high risk of ending up without any embryo suitable for transfer after (several) stimulation cycles, especially in AMA patients. Patients should be informed in detail about the frequency of inconclusive or mosaic results, with the associated risk of not having an euploid embryo available for transfer after PGT-A, as well as the high cost involved in this type of testing.

Healthy Live Births after the Transfer of Mosaic Embryos: Self-Correction or PGT-A Overestimation?

The implementation of next generation sequencing (NGS) in preimplantation genetic testing for aneuploidy (PGT-A) has led to a higher prevalence of mosaic diagnosis within the trophectoderm (TE) sample. Regardless, mosaicism could potentially increase the rate of live-born children with chromosomic syndromes, though available data from the transfer of embryos with putative PGT-A mosaicism are scarce but reassuring. Even with lower implantation and higher miscarriage rates, mosaic embryos can develop into healthy live births. Therefore, this urges an explanation for the disappearance of aneuploid cells throughout development, to provide guidance in the management of mosaicism in clinical practice. Technical overestimation of mosaicism, together with some sort of "self-correction" mechanisms during the early post-implantation stages, emerged as potential explanations. Unlike the animal model, in which the elimination of genetically abnormal cells from the future fetal lineage has been demonstrated, in human embryos this capability remains unverified even though the germ layer displays an aneuploidy-induced cell death lineage preference with higher rates of apoptosis in the inner cell mass (ICM) than in the TE cells. Moreover, the reported differential dynamics of cell proliferation and apoptosis between euploid, mosaic, and aneuploid embryos, together with pro-apoptosis gene products (cfDNA and mRNA) and extracellular vesicles identified in the blastocoel fluid, may support the hypothesis of apoptosis as a mechanism to purge the preimplantation embryo of aneuploid cells. Alternative hypotheses, like correction of aneuploidy by extrusion of a trisomy chromosome or by monosomic chromosome duplication, are even, though they represent an extremely rare phenomenon. On the other hand, the technical limitations of PGT-A analysis may lead to inaccuracy in embryo diagnoses, identifying as "mosaic" those embryos that are uniformly euploid or aneuploid. NGS assumption of "intermediate copy number profiles" as evidence of a mixture of euploid and aneuploid cells in a single biopsy has been reported to be poorly predictive in cases of mosaicism diagnosis. Additionally, the concordance found between the TE and the ICM in cases of TE biopsies displaying mosaicism is lower than expected, and it correlates differently depending on the type (whole chromosome versus segmental) and the level of mosaicism reported. Thus, in cases of low-/medium-level mosaicism (<50%), aneuploid cells would rarely involve the ICM and other regions. However, in high-level mosaics (≥50%), abnormal cells in the ICM should display higher prevalence, revealing more uniform aneuploidy in most embryos, representing a technical variation in the uniform aneuploidy range, and therefore might impair the live birth rate.

Clinical management of mosaic results from preimplantation genetic testing for aneuploidy of blastocysts: a committee opinion

This revised document incorporates a growing number of published studies about mosaic embryo transfer and provides current evidence-based considerations for the clinical management of embryos with mosaic results on preimplantation genetic testing for aneuploidy. This document replaces the document titled "Clinical management of mosaic results from preimplantation genetic testing for aneuploidy (PGT-A) of blastocysts: a committee opinion," published in 2020 (Fertil Steril 2020;114:246-54).

Update on preimplantation genetic testing for aneuploidy and outcomes of embryos with mosaic results

Preimplantation genetic testing for aneuploidy (PGT-A) is used as a frequent add-on for in-vitro fertilization (IVF) to improve clinical outcomes. The purpose is to select a euploid embryo following chromosomal testing on embryo biopsies. The current practice includes comprehensive chromosome screening (CCS) technology applied on trophectoderm (TE) biopsies. Despite its widespread use, PGT-A remains a controversial topic mainly because all of the RCTs comprised only good prognosis patients with 2 or more blastocysts available; hence the results are not generalizable to all groups of patients. Furthermore, with the introduction of the highly-sensitive platforms into clinical practice (i.e. next-generation sequencing [NGS]), a result consistent with intermediate copy number surfaced and is termed "Mosaic," consistent with a mixture of euploid and aneuploid cells within the biopsy sample. The optimal disposition and management of embryos with mosaic results is still an open question, as many 'mosaics' generated healthy live births with no identifiable congenital anomalies. The present article provides a complete and comprehensive up-to-date review on PGT-A. It discusses in detail the findings of all the published RCTs on PGT-A with CCS, comments on the subject of "mosaicism" and its current management, and describes the latest technique of non-invasive PGT-A.

The nature of embryonic mosaicism across female age spectrum: an analysis of 21,345 preimplantation genetic testing for aneuploidy cycles

Objective

To understand how mosaicism varies across patient-specific variables and clinics.

Design

Cross-sectional cohort.

Setting

Genetic testing laboratory.

Patients

A total of 86,208 embryos from 17,366 patients underwent preimplantation genetic testing for aneuploidy using next-generation sequencing.

Interventions

Mosaic embryos were classified as either low-level (20%-40%) or high-level (40%-80%) and by type of mosaic error: single segmental, complex segmental, single chromosome, or complex abnormal mosaic. The rate of mosaicism was stratified by the Society for Assisted Reproductive Technology age categories: <35 years, 35-37 years, 38-40 years, 41-42 years, and >42 years.

Main Outcome Measures

Distribution of chromosomal findings and prevalence of mosaicism type by age. Probability of creating mosaic embryos in a subsequent cycle.

Results

Among all embryos, 44% were euploid, 40.2% were aneuploid, and 15.8% were mosaic. Both low-level and high-level mosaicism were more prevalent among younger patients. Of all mosaic embryos, the youngest age cohort <35 years had the highest proportions of single and complex segmental mosaicism (37.9% and 6.8%, respectively), whereas those aged >42 years had the highest single whole chromosome and complex abnormal mosaicism (37.1% and 34.0%, respectively). Although there was variability in mosaic rates across clinics, the median mosaic rate over 3 years ranged from 14.48% to 17.72%. A diagnosis of a mosaic embryo in a previous cycle did not increase a patient's odds for having a mosaic embryo in a subsequent cycle.

Conclusions

Mosaicism is overall higher in younger patients, but the complexity of mosaic errors increases with age. A history of mosaicism was not associated with mosaicism in subsequent cycles. Additional research is needed to understand the etiologies of the various subtypes of mosaic embryos and clinical outcomes associated with their transfer.

Case report: Prenatal diagnosis of rare chromosome mosaicism: discordant results between chorionic villi and amniotic fluid samples

Objective: We described a unique case of near-negative chromosome mosaicism in chorionic villi but complete monosomy X in amniotic fluid. Methods: Chorionic villus sampling and amniocentesis were performed separately in the first and second trimesters. Chromosomal microarray (CMA) and rapid aneuploidy detection (QF-PCR and FISH) were performed on placental villi and uncultured amniotic fluid. After pregnancy termination, the placenta, umbilical cord, and fetal muscle tissues were sampled for FISH detection. Results: The CMA revealed a lower signal from chromosome X in chorionic villi, with a copy number of 1.85, implying the presence of mosaic monosomy X. However, the QF-PCR and FISH results were nearly normal. In uncultured amniotic fluid, CMA and rapid aneuploidy detection indicated complete monosomy X. Across different sampling points on the aborted fetus, the FISH results varied from normal, to mosaic, and then complete monosomy X. Conclusion: This case presents a rare and complex situation where sampling from uncultured chorionic villi indicated low-level chromosome mosaicism, while sampling from amniotic fluid revealed complete monosomy X. Although some of these discordant outcomes may be due to methodological limitations, we conclude that prenatal consultation should be combined with fetal ultrasound phenotype and genetic testing for a comprehensive evaluation of fetal genetic abnormalities.

Sperm deoxyribonucleic acid fragmentation index at the time of intracytoplasmic sperm injection and standard in vitro fertilization is correlated with lower fertilization but not with blastocyst genetic diagnosis

Objective

To determine the effects of sperm deoxyribonucleic acid (DNA) fragmentation at the time of fertilization on in vitro fertilization (IVF) outcomes and genetic diagnosis using next generation sequencing.

Design

Prospective double-blinded study.

Setting

Private Clinic.

Patients

Couples (n = 150).

Intervention

In vitro fertilization with preimplantation genetic testing for aneuploidy and sperm DNA fragmentation assay, as in sperm chromatin structure assay the day of retrieval.

Main Outcome Measures

Laboratory outcomes are listed in the results section. Statistical analysis was performed using JMP, XYLSTAT, and STATA version 15.

Results

The sperm DNA fragmentation index (DFI) in the neat ejaculate did not predict fertilization rate, quality, blastulation, or genetic diagnosis. No statistically significant results were obtained comparing <15% with >15%, <20% with >20%, <30% with >30% except for DFI. No statistically significant differences in oocyte source age or male age were observed. No statistically significant differences comparing <15% with >15%, <20% with >20%, <30% with >30% DFI at the time of standard IVF or intracytoplasmic sperm injection (ICSI) were observed for % euploid, aneuploid, mosaic, blastulation, biopsied, or D5/total biopsied. The DFI of >15% had more good quality D3 embryos than the <15% group, as did the >20% group compared with the <20% group. The ICSI fertilization was significantly higher in all 3 lower percentage groups compared with the higher counterpart. Standard IVF had significantly more blastocysts/fertilized suitable for biopsy and more D5/total number biopsied than ICSI embryos despite no difference in DFI.

Conclusions

The DFI at fertilization is correlated with decreased fertilization for ICSI and IVF.

Metaphase-II oocyte competence is unlinked to the gonadotrophins used for ovarian stimulation: a matched case-control study in women of advanced maternal age

PURPOSE

An impact of different gonadotrophins selection for ovarian stimulation (OS) on oocyte competence has yet to be defined. In this study, we asked whether an association exists between OS protocol and euploid blastocyst rate (EBR) per metaphase-II (MII) oocytes.

METHODS

Cycles of first preimplantation genetic testing for aneuploidies conducted by women ≥ 35 years old with their own metaphase-II oocytes inseminated in the absence of severe male factor (years 2014-2018) were clustered based on whether recombinant FSH (rec-FSH) or human menopausal gonadotrophin (HMG) was used for OS, then matched for the number of fresh inseminated eggs. Four groups were outlined: rec-FSH (N = 57), rec-FSH plus rec-LH (N = 55), rec-FSH plus HMG (N = 112), and HMG-only (N = 127). Intracytoplasmic sperm injection, continuous blastocyst culture, comprehensive chromosome testing to assess full-chromosome non-mosaic aneuploidies and vitrified-warmed euploid single embryo transfers (SETs) were performed. The primary outcome was the EBR per cohort of MII oocytes. The secondary outcome was the live birth rate (LBR) per first SETs.

RESULTS

Rec-FSH protocol was shorter and characterized by lower total gonadotrophin (Gn) dose. The linear regression model adjusted for maternal age showed no association between the Gn adopted for OS and EBR per cohort of MII oocytes. Similarly, no association was reported with the LBR per first SETs, even when adjusting for blastocyst quality and day of full blastulation.

CONCLUSION

In view of enhanced personalization in OS, clinicians shall focus on different endpoints or quantitative effects related to Gn action towards follicle recruitment, development, and atresia. Here, LH and/or hCG was administered exclusively to women with expected sub/poor response; therefore, we cannot exclude that specific Gn formulations may impact patient prognosis in other populations.

Preimplantation genetic testing for aneuploidy: The management of mosaic embryos

As the resolution and accuracy of diagnostic techniques for preimplantation genetic testing for aneuploidy (PGT-A) are improving, more mosaic embryos are being identified. Several studies have provided evidence that mosaic embryos have reproductive potential for implantation and healthy live birth. Notably, mosaic embryos with less than 50% aneuploidy have yielded a live birth rate similar to euploid embryos. This concept has led to a major shift in current PGT-A practice, but further evidence and theoretically relevant data are required. Proper guidelines for selecting mosaic embryos suitable for transfer will reduce the number of discarded embryos and increase the chances of successful embryo transfer. We present an updated review of clinical outcomes and practice recommendations for the transfer of mosaic embryos using PGT-A.

Morphological and morphokinetic associations with aneuploidy: a systematic review and meta-analysis

BACKGROUND

A time lapse system (TLS) is utilized in some fertility clinics with the aim of predicting embryo viability and chance of live birth during IVF. It has been hypothesized that aneuploid embryos display altered morphokinetics as a consequence of their abnormal chromosome complement. Since aneuploidy is one of the fundamental reasons for IVF failure and miscarriage, attention has focused on utilizing morphokinetics to develop models to non-invasively risk stratify embryos for ploidy status. This could avoid or reduce the costs associated with pre-implantation genetic testing for aneuploidy (PGT-A). Furthermore, TLS have provided an understanding of the true prevalence of other dysmorphisms. Hypothetically, the incorporation of morphological features into a model could act synergistically, improving a model's discriminative ability to predict ploidy status.

OBJECTIVE AND RATIONALE

The aim of this systematic review and meta-analysis was to investigate associations between ploidy status and morphokinetic or morphological features commonly denoted on a TLS. This will determine the feasibility of a prediction model for euploidy and summarize the most useful prognostic markers to be included in model development.

SEARCH METHODS

Five separate searches were conducted in Medline, Embase, PubMed and Cinahl from inception to 1 July 2021. Search terms and word variants included, among others, PGT-A, ploidy, morphokinetics and time lapse, and the latter were successively substituted for the following morphological parameters: fragmentation, multinucleation, abnormal cleavage and contraction. Studies were limited to human studies.

OUTCOMES

Overall, 58 studies were included incorporating over 40 000 embryos. All except one study had a moderate risk of bias in at least one domain when assessed by the quality in prognostic studies tool. Ten morphokinetic variables were significantly delayed in aneuploid embryos. When excluding studies using less reliable genetic technologies, the most notable variables were: time to eight cells (t8, 1.13 h, 95% CI: 0.21-2.05; three studies; n = 742; I2 = 0%), t9 (2.27 h, 95% CI: 0.5-4.03; two studies; n = 671; I2 = 33%), time to formation of a full blastocyst (tB, 1.99 h, 95% CI 0.15-3.81; four studies; n = 1640; I2 = 76%) and time to expanded blastocyst (tEB, 2.35 h, 95% CI: 0.06-4.63; four studies; n = 1640; I2 = 83%). There is potentially some prognostic potential in the degree of fragmentation, multinucleation persisting to the four-cell stage and frequency of embryo contractions. Reverse cleavage was associated with euploidy in this meta-analysis; however, this article argues that these are likely spurious results requiring further investigation. There was no association with direct unequal cleavage in an embryo that progressed to a blastocyst, or with multinucleation assessed on Day 2 or at the two-cell stage. However, owing to heterogeneous results and poor-quality evidence, associations between these morphological components needs to be investigated further before conclusions can be reliably drawn.

WIDER IMPLICATIONS

This first systematic review and meta-analysis of morphological and morphokinetic associations with ploidy status demonstrates the most useful morphokinetic variables, namely t8, t9 and tEB to be included in future model development. There is considerable variability within aneuploid and euploid embryos making definitively classifying them impossible; however, it is feasible that embryos could be prioritized for biopsy. Furthermore, these results support the mechanism by which algorithms for live birth may have predictive ability, suggesting aneuploidy causes delayed cytokinesis. We highlight significant heterogeneity in our results secondary to local conditions and diverse patient populations, therefore calling for future models to be robustly developed and tested in-house. If successful, such a model would constitute a meaningful breakthrough when accessing PGT-A is unsuitable for couples.

Human blastocyst spontaneous collapse is associated with worse morphological quality and higher degeneration and aneuploidy rates: a comprehensive analysis standardized through artificial intelligence

STUDY QUESTION

What are the factors associated with human blastocyst spontaneous collapse and the consequences of this event?

SUMMARY ANSWER

Approximately 50% of blastocysts collapsed, especially when non-viable, morphologically poor and/or aneuploid.

WHAT IS KNOWN ALREADY

Time-lapse microscopy (TLM) is a powerful tool to observe preimplantation development dynamics. Lately, artificial intelligence (AI) has been harnessed to automate and standardize such observations. Here, we adopted AI to comprehensively portray blastocyst spontaneous collapse, namely the phenomenon of reduction in size of the embryo accompanied by efflux of blastocoel fluid and the detachment of the trophectoderm (TE) from the zona pellucida (ZP). Although the underlying causes are unknown, blastocyst spontaneous collapse deserves attention as a possible marker of reduced competence.

STUDY DESIGN, SIZE, DURATION

An observational study was carried out, including 2348 TLM videos recorded during preimplantation genetic testing for aneuploidies (PGT-A, n = 720) cycles performed between January 2013 and December 2020. All embryos in the analysis at least reached the time of starting blastulation (tSB), 1943 of them reached full expansion, and were biopsied and then vitrified.

PARTICIPANTS/MATERIALS, SETTING, METHODS

ICSI, blastocyst culture, TE biopsy without Day 3 ZP drilling, comprehensive chromosome testing and vitrification were performed. The AI software automatically registered tSB and time of expanding blastocyst (tEB), start and end time of each collapse, time between consecutive collapses, embryo proper area, percentage of shrinkage, embryo:ZP ratio at embryo collapse, time of biopsy (t-biopsy) and related area of the fully (re-)expanded blastocyst before biopsy, time between the last collapse and biopsy. Blastocyst morphological quality was defined according to both Gardner's criteria and an AI-generated implantation score. Euploidy rate per biopsied blastocyst and live birth rate (LBR) per euploid single embryo transfer (SET) were the main outcomes. All significant associations were confirmed through regression analyses. All couple, cycle and embryo main features were also investigated for possible associations with blastocyst spontaneous collapse.

MAIN RESULTS AND THE ROLE OF CHANCE

At least one collapsing embryo (either viable or subsequently undergoing degeneration) was recorded in 559 cycles (77.6%) and in 498 cycles (69.2%) if considering only viable blastocysts. The prevalence of blastocyst spontaneous collapse after the tSB, but before the achievement of full expansion, was 50% (N = 1168/2348), irrespective of cycle and/or couple characteristics. Blastocyst degeneration was 13% among non-collapsing embryos, while it was 18%, 20%, 26% and 39% among embryos collapsing once, twice, three times or ≥4 times, respectively. The results showed that 47.3% (N = 918/1943) of the viable blastocysts experienced at least one spontaneous collapse (ranging from 1 up to 9). Although starting from similar tSB, the number of spontaneous collapses was associated with a delay in both tEB and time of biopsy. Of note, the worse the quality of a blastocyst, the more and the longer its spontaneous collapses. Blastocyst spontaneous collapse was significantly associated with lower euploidy rates (47% in non-collapsing and 38%, 32%, 31% and 20% in blastocysts collapsing once, twice, three times or ≥4 times, respectively; multivariate odds ratio 0.78, 95%CI 0.62-0.98, adjusted P = 0.03). The difference in the LBR after euploid vitrified-warmed SET was not significant (46% and 39% in non-collapsing and collapsing blastocysts, respectively).

LIMITATIONS, REASONS FOR CAUTION

An association between chromosomal mosaicism and blastocyst collapse cannot be reliably assessed on a single TE biopsy. Gestational and perinatal outcomes were not evaluated. Other culture strategies and media should be tested for their association with blastocyst spontaneous collapse. Future studies with a larger sample size are needed to investigate putative impacts on clinical outcomes after euploid transfers.

WIDER IMPLICATIONS OF THE FINDINGS

These results demonstrate the synergistic power of TLM and AI to increase the throughput of embryo preimplantation development observation. They also highlight the transition from compaction to full blastocyst as a delicate morphogenetic process. Blastocyst spontaneous collapse is common and associates with inherently lower competence, but additional data are required to deepen our knowledge on its causes and consequences.

STUDY FUNDING/COMPETING INTEREST(S)

There is no external funding to report. I.E., A.B.-M., I.H.-V. and B.K. are Fairtility employees. I.E. and B.K. also have stock or stock options of Fairtility.

TRIAL REGISTRATION NUMBER

N/A.

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.

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.

Live Birth with or without Preimplantation Genetic Testing for Aneuploidy

BACKGROUND

Embryo selection with preimplantation genetic testing for aneuploidy (PGT-A) may improve pregnancy outcomes after initial embryo transfer. However, it remains uncertain whether PGT-A improves the cumulative live-birth rate as compared with conventional in vitro fertilization (IVF).

METHODS

In this multicenter, randomized, controlled trial, we randomly assigned subfertile women with three or more good-quality blastocysts to undergo either PGT-A or conventional IVF; all the women were between 20 and 37 years of age. Three blastocysts were screened by next-generation sequencing in the PGT-A group or were chosen by morphologic criteria in the conventional-IVF group and then were successively transferred one by one. The primary outcome was the cumulative live-birth rate after up to three embryo-transfer procedures within 1 year after randomization. We hypothesized that the use of PGT-A would result in a cumulative live-birth rate that was no more than 7 percentage points higher than the rate after conventional IVF, which would constitute the noninferiority margin for conventional IVF as compared with PGT-A.

RESULTS

A total of 1212 patients underwent randomization, and 606 were assigned to each trial group. Live births occurred in 468 women (77.2%) in the PGT-A group and in 496 (81.8%) in the conventional-IVF group (absolute difference, -4.6 percentage points; 95% confidence interval [CI], -9.2 to -0.0; P<0.001). The cumulative frequency of clinical pregnancy loss was 8.7% and 12.6%, respectively (absolute difference, -3.9 percentage points; 95% CI, -7.5 to -0.2). The incidences of obstetrical or neonatal complications and other adverse events were similar in the two groups.

CONCLUSIONS

Among women with three or more good-quality blastocysts, conventional IVF resulted in a cumulative live-birth rate that was noninferior to the rate with PGT-A. (Funded by the National Natural Science Foundation of China and others; ClinicalTrials.gov number, NCT03118141.).

Let the data do the talking: the need to consider mosaicism during embryo selection

Chromosomal mosaicism, the coexistence of cells with different chromosomal content, has been documented in human embryos for 3 decades. Early versions of preimplantation genetic testing for aneuploidy (PGT-A) did not measure mosaicism, either because typically only a single cell was assessed or because the technique could not accurately identify it. Although this led to a straightforward diagnosis (an embryo was considered either normal or abnormal), it simply avoided the issue and, in hindsight, may have led to numerous misdiagnoses with negative clinical consequences. Modern PGT-A evaluates a multicellular biopsy specimen with techniques capable of recognizing intermediate copy number signals for chromosomes or subchromosomal regions. We are, therefore, inevitably confronted with the issue of mosaicism and the challenge of managing embryos producing such results in the clinic. Here we discuss recent data showing that not only mosaicism in general, but specific features of mosaicism detected with PGT-A, are associated with variable clinical outcomes. The conclusion is evident: mosaicism should be considered for more informed and improved embryo selection in the clinic.

Evidence-based clinical prioritization of embryos with mosaic results: a systematic review and meta-analysis

PURPOSE

The purpose of this review and meta-analysis is to standardize the practice of mosaic embryo transfer, based on the current available evidence.

METHODS

This is a systematic review and meta-analysis. Relevant studies published were comprehensively selected using PubMed, Medline, Embase, and CENTRAL until 5 March 2021. Prospective and retrospective studies reporting the genetic analysis and clinical outcomes of mosaic embryo transfer were included. Risk of bias assessment was based on the Newcastle-Ottawa scale for the non-randomized studies. The primary and secondary outcomes were combined ongoing pregnancy and live birth rate and miscarriage rate, respectively.

RESULTS

There were no differences between low and high mosaic embryos when a cut-off of 40% was used in terms of OP/LBR and SAB. However, low mosaics with a cut-off of 50% compared to high mosaics showed a significantly higher OP/LBR in the NGS but not in the a-CGH group, and a significantly lower risk of SAB. No differences were noted between mosaic monosomies versus trisomies and single versus double mosaics for both OP/LBR and SAB. Finally, segmental mosaics showed a higher OP/LBR and a lower SAB compared to whole chromosomes, and single and double mosaics had a higher OP/LBR compared to complex mosaics.

CONCLUSIONS

A cut-off of 50% in defining low versus high mosaic embryos is preferable to a threshold of 40% when using NGS platform. No priority was established for mosaic trisomies over monosomies. Single and double mosaics must be preferred over complex mosaics and segmental mosaics must be preferred over whole chromosome mosaics. These results should be interpreted in the context of specific chromosomes involved in the mosaicism.

Non-invasive preimplantation genetic testing for putative mosaic blastocysts: a pilot study

STUDY QUESTION

What is the potential of applying non-invasive preimplantation genetic testing (niPGT) for chromosome abnormalities in blastocysts reported with a mosaic trophectoderm (TE) biopsy?

SUMMARY ANSWER

niPGT of cell-free DNA in blastocyst culture medium exhibited a good diagnostic performance in putative mosaic blastocysts.

WHAT IS KNOWN ALREADY

Advances in niPGT have demonstrated the potential reliability of cell-free DNA as a resource for genetic assessment, but information on mosaic embryos is scarce because the mosaicism may interfere with niPGT. In addition, the high incidence of mosaicism reported in the context of PGT and the viability of mosaic blastocysts raise questions about whether mosaicism really exists.

STUDY DESIGN, SIZE, DURATION

The study was performed between May 2020 and July 2020. First, clinical data collected by a single-center over a 6-year period on PGT for chromosome aneuploidies (PGT-A) or chromosomal structural rearrangements (PGT-SR) were analyzed. After confirming the reliability of niPGT, 41 blastocysts classified as mosaics by trophectoderm (TE) biopsy were re-cultured. The chromosomal copy number of the blastocyst embryo (BE, the gold standard), TE re-biopsy, and corresponding cell-free DNA in the culture medium was assessed.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Data on patients enrolled for PGT at a single center from 2014 to 2019 were collected and the cycles with available putative mosaic blastocysts were evaluated. To verify the diagnostic validity of niPGT, eight aneuploid blastocysts were thawed and re-cultured for 14-18 h. The concordance of the niPGT diagnosis results and the whole blastocyst testing results was analyzed. Forty-one blastocysts reported as mosaics from 22 patients were included and re-cultured for 14-18 h. The genetic material of the BE, TE re-biopsy, and corresponding cell-free DNA in the culture medium was amplified using multiple annealing and looping-based amplification cycles. The karyotype data from niPGT and TE re-biopsy were compared with that from the whole blastocyst, and the efficiency of niPGT was assessed.

MAIN RESULTS AND THE ROLE OF CHANCE

Data on 3738 blastocysts from 785 PGT-A or PGT-SR cycles of 677 patients were collected. According to the TE biopsy report, of the 3662 (98%) successfully amplified samples, 24 (0.6%) yielded no results, 849 (23.2%) were euploid, 2245 (61.3%) were aneuploid, and 544 (14.9%) were mosaic. Sixty patients without euploid blastocysts opted for a single mosaic blastocyst transfer, and 30 (50%) of them obtained a clinical pregnancy. With the BE chromosome copy number as the gold standard, niPGT and TE re-biopsy showed reliable detection ability and diagnostic efficiency in eight putative aneuploid blastocysts. Of the 41 putative mosaic blastocysts re-cultured and re-tested, 35 (85.4%) showed euploid BE results. All but two of the blastocysts previously diagnosed with segmental chromosomal mosaic were actually euploid. In addition, all blastocysts previously classified as low degree (20-50%) mosaics were identified as euploid by BE PGT, whereas four of the six putative high degree (50-80%) mosaic blastocysts showed chromosomal abnormalities. The raw concordance rates of spent culture medium (SCM) and TE re-biopsies compared with BE were 74.4% and 82%, respectively, in terms of overall ploidy and 96.2% and 97.6%, respectively, per single chromosome when considering all degree mosaic results as true positives. However, when we set a mosaicism identification threshold of 50%, the concordance rates of SCM and TE re-biopsies compared with BE were 87.2% and 85% at the overall ploidy level and 98.8% and 98.3% at the chromosomal level, respectively. At the full ploidy level, the sensitivity and false negative rates for niPGT were 100% and 0, respectively. After adjustment of the threshold for mosaicism, the specificity of niPGT increased from 69.7% to 84.8% in terms of overall ploidy and from 96.1% to 98.9% at the chromosomal level.

LIMITATIONS, REASONS FOR CAUTION

The primary limitation of this study is the small sample size, which decreases the strength of our conclusions. If possible, identifying the clinical outcome of niPGT on reassessed mosaic blastocysts would be further progress in this field.

WIDER IMPLICATIONS OF THE FINDINGS

This study is the first to explore the practicability of niPGT in diagnostic reassessment of putative mosaicism. The present study provides a novel opportunity for patients with only mosaic blastocysts and no euploid blastocysts, regardless of the technical or biological basis of mosaicism. Employing niPGT after 14-18 h of re-culturing might be a superior option for the best use of blastocysts because of its minimally invasive nature.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by grants from National Key Technology Research and Development Program of China (No. 2017YFC1002004), the Central Guiding the Science and Technology Development of the Local (2018080802D0081) and College Natural Science Project of Anhui Province (KJ2019A0287). There are no competing interests to declare.

TRIAL REGISTRATION NUMBER

N/A.

Embryo quality, ploidy, and transfer outcomes in male versus female blastocysts

PURPOSE

The goal is to determine if variations exist between male and female blastocysts in preimplantation measurements of quality and ploidy and in vitro fertilization elective single-embryo transfer (eSET) outcomes.

METHODS

A retrospective chart review was conducted from a private fertility center's database of blastocysts undergoing preimplantation genetic testing for aneuploidy, along with details of eSET from this screened cohort. Main outcomes included preimplantation embryo quality and sex-specific eSET outcomes.

RESULTS

A total of 3708 embryos from 578 women were evaluated, with 45.9% male and 54.1% female. The majority were High grade. No difference existed between embryo sex and overall morphological grade, inner cell mass or trophectoderm grade, or blastocyst transformation day. Female blastocysts had a higher aneuploidy rate than male blastocysts (P < 0.001). Five hundred thirty-nine eSETs from 392 women were evaluated, with High grade embryos more likely to have implantation (P < 0.001), clinical pregnancy (P < 0.001), and ongoing pregnancy (P = 0.018) than Mid or Low grade embryos. Day 5 blastocysts were more likely to have implantation (P = 0.018), clinical pregnancy (P = 0.005), and ongoing pregnancy (P = 0.018) than day 6 blastocysts. Male and female embryos had similar transfer outcomes, although female day 5 blastocysts were more likely to result in clinical pregnancy (P = 0.012), but not ongoing pregnancy, than female day 6 blastocysts. Male eSET outcomes did not differ by blastocyst transformation day.

CONCLUSION

Male and female embryos have comparable grade and quality; however, female embryos were more likely to be aneuploid. Ongoing pregnancy rates did not differ by embryo sex. Day 5 embryos had more favorable transfer outcomes than day 6 embryos.

Confined placental mosaicism and the association with pregnancy outcome and fetal growth: a review of the literature

BACKGROUND

Chromosomal mosaicism can be detected in different stages of early life: in cleavage stage embryos, in blastocysts and biopsied cells from blastocysts during preimplantation genetic testing for aneuploidies (PGT-A) and later during prenatal testing, as well as after birth in cord blood. Mosaicism at all different stages can be associated with adverse pregnancy outcomes. There is an onward discussion about whether blastocysts diagnosed as chromosomally mosaic by PGT-A should be considered safe for transfer. An accurate diagnosis of mosaicism remains technically challenging and the fate of abnormal cells within an embryo remains largely unknown. However, if aneuploid cells persist in the extraembryonic tissues, they can give rise to confined placental mosaicism (CPM). Non-invasive prenatal testing (NIPT) uses cell-free (cf) DNA released from the placenta in maternal blood, facilitating the detection of CPM. In literature, conflicting evidence is found about whether CPM is associated with fetal growth restriction (FGR) and/or other pregnancy outcomes. This makes counselling for patients by clinicians challenging and more knowledge is needed for clinical decision and policy making.

OBJECTIVE AND RATIONALE

The objective of this review is to evaluate the association between CPM and prenatal growth and adverse pregnancy outcomes. All relevant literature has been reviewed in order to achieve an overview on merged results exploring the relation between CPM and FGR and other adverse pregnancy outcomes.

SEARCH METHODS

The following Medical Subject Headings (MESH) terms and all their synonyms were used: placental, trophoblast, cytotrophoblast, mosaicism, trisomy, fetal growth, birth weight, small for gestational age and fetal development. A search in Embase, PubMed, Medline Ovid, Web of Science, Cochrane Central Register of Controlled Trials (CENTRAL) and Google Scholar databases was conducted. Relevant articles published until 16 July 2020 were critically analyzed and discussed.

OUTCOMES

There were 823 articles found and screened based on their title/abstract. From these, 213 articles were selected and full text versions were obtained for a second selection, after which 70 publications were included and 328 cases (fetuses) were analyzed. For CPM in eight different chromosomes (of the total 14 analyzed), there was sufficient evidence that birth weight was often below the 5th percentile of fetal growth standards. FGR was reported in 71.7% of CPM cases and preterm birth (<37 weeks of delivery) was reported in 31.0% of cases. A high rate of structural fetal anomalies, 24.2%, in cases with CPM was also identified. High levels of mosaicism in CVS and presence of uniparental disomy (UPD) were significantly associated with adverse pregnancy outcomes.

WIDER IMPLICATIONS

Based on the literature, the advice to clinicians is to monitor fetal growth intensively from first trimester onwards in case of CPM, especially when chromosome 2, 3, 7, 13, 15, 16 and 22 are involved. In addition to this, it is advised to examine the fetuses thoroughly for structural fetal anomalies and raise awareness of a higher chance of (possibly extreme) premature birth. Despite prematurity in nearly a fifth of cases, the long-term follow-up of CPM life borns seems to be positive. More understanding of the biological mechanisms behind CPM will help in prioritizing embryos for transfer after the detection of mosaicism in embryos through PGT-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.

An overview of the current and emerging platforms for preimplantation genetic testing for aneuploidies (PGT-A) in in vitro fertilization programs

Preimplantation genetic testing for aneuploidies (PGT-A) and PGT for monogenic disorders (PGT-M) have currently been used widely, aiming to improve IVF outcomes. Although with many years of unsatisfactory results, PGT-A has been revived because new technologies have been adopted, such as platforms to examine all 24 types of chromosomes in blastocysts. This report compiles current knowledge regarding the available PGT platforms, including quantitative PCR, array CGH, and next-generation sequencing. The diagnostic capabilities of are compared and respective advantages/disadvantages outlined. We also address the limitations of current technologies, such as assignment of embryos with balanced translocation. We also discuss the emerging novel PGT technologies that likely will change our future practice, such as non-invasive PGT examining spent culture medium. Current literature suggest that most platforms can effectively reach concordant results regarding whole-chromosome ploidy status of all 24 types of chromosomes. However, different platforms have different resolutions and experimental complexities; leading to different turnaround time, throughput and differential capabilities of detecting mosaicism, segmental mutations, unbalanced translocations, concurrent PGT-A and PGT-M etc. Based on these information, IVF staff can more appropriately interpret PGT data and counsel patients, and select suitable platforms to meet personalized needs. The present report also concisely discusses some crucial clinical outcomes by PGT, which can clarify the role of applying PGT in daily IVF programs. Finally the up-to-date information about the novel use of current technologies and the newly emerging technologies will also help identify the focus areas for the design of new platforms for PGT in the future.

Clinical management of mosaic results from preimplantation genetic testing for aneuploidy (PGT-A) of blastocysts: a committee opinion

Since the advent of preimplantation genetic testing for aneuploidy (PGT-A) in the 1990s, substantial changes in test methodology and technology now allow the detection and reporting of intermediate chromosome copy number (commonly referred to as mosaicism) for aneuploidy in a trophectoderm biopsy sample. Clinicians are grappling with how to interpret such findings and how to counsel patients about embryo transfer decision-making. This document reviews the available literature and outlines the various issues surrounding the reporting of intermediate copy number and consideration of storage or transfer of blastocysts with intermediate copy number results. This document does not endorse, nor does it suggest that PGT-A is appropriate for all cases of in vitro fertilization.

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.

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.

Commentary on two recently published formal guidelines on management of "mosaic" embryos after preimplantation genetic testing for aneuploidy (PGT-A)

Two professional societies recently published opinions on the clinical management of "mosaic" results from preimplantation genetic testing for aneuploidy (PGT-A) in human blastocyst-stage embryos in associations with in vitro fertilization (IVF). We here point out three principal shortcomings: (i) Though a most recent societal opinion states that it should not be understood as an endorsement of the use of PGT-A, any discussion of how PGT-A should be clinically interpreted for all practical purposes does offer such an endorsement. (ii) The same guideline derived much of its opinion from a preceding guidance in favor of utilization of PGT-A that did not follow even minimal professional requirements for establishment of practice guidelines. (iii) Published guidelines on so-called "mosaic" embryos from both societies contradict basic biological characteristics of human preimplantation-stage embryos. They, furthermore, are clinically unvalidated and interpret results of a test, increasingly seen as harmful to IVF outcomes for many infertile women. Qualified professional organizations, therefore, should finally offer transparent guidelines about the utilization of PGT-A in association with IVF in general.

A workflow for simultaneous DNA copy number and methylome analysis of inner cell mass and trophectoderm cells from human blastocysts

OBJECTIVE

To establish a workflow for isolating single trophectoderm (TE) and inner cell mass (ICM) cells and to simultaneously evaluate these cells for copy number variation (CNV) as well as methylome development.

DESIGN

Experimental.

SETTING

Academic medical center.

PATIENT(S)

Donated genetically abnormal blastocysts.

INTERVENTION(S)

Single cells were isolated, followed by bisulfite conversion and sequencing to identify CNV and methylome profiles.

MAIN OUTCOME MEASURE(S)

CNV and methylation profiling.

RESULT(S)

Two embryos were dissociated, isolating 46 single cells, with 17 ICM and 12 TE cells selected for further downstream analysis. Chromosome ploidies and embryo sex were concordant with the results from conventional aneuploidy testing. In 3 of the 29 cells, additional aneuploidies were discovered, indicating possible mosaicism undetected by routine preimplantation genetic testing for aneuploidy. CpG methylation frequency was higher in ICM cells compared with TE cells (44.3% vs. 32.4%), respectively, while non-CpG methylation frequency was similar among both cell types. CpG methylation levels accurately distinguished ICM from TE cells epigenetically.

CONCLUSION(S)

We describe an effective workflow for isolating and sequencing single ICM and TE cells from human blastocysts. The use of methylation profiling can help distinguish these two cell populations better then morphologic identification alone. TE cells had significantly lower levels of DNA methylation, which may be explained in part by the fact that these cells have begun the process of differentiation and are transcriptionally more active than ICM. This approach may be used to explore the genetic complexities within human embryos, specifically among the two primary cell types seen at this stage of development.

When embryology meets genetics: the definition of developmentally incompetent preimplantation embryos (DIPE)-the consensus of two Italian scientific societies

A clear definition of developmentally incompetent preimplantation embryo (DIPE) in literature is still missing, while several scientific societies are discussing this challenging topic. From both a clinical and scientific perspective, the identification of embryos unfit for reproductive purpose is crucial. This aim should be pursued in light of all diagnostic technologies for embryo evaluation, encompassing also genetic analyses, of recent implementation in IVF. The Italian context is characterized by an unusual scenario: embryos can be discarded only if not viable and cannot be used for research purposes either. Therefore, thousands of embryos, diagnosed as affected and/or aneuploid as resulting from preimplantation genetic testing (PGT) and clinically not utilizable, are cryopreserved and stored indefinitely, with important psychological, legal, and financial implications. With the aim of updating the definition of DIPE, also on the basis of the embryo genetic status, the Italian Society of Embryology, Reproduction and Research (SIERR) and the Italian Society of Human Genetic (SIGU) reviewed the literature on this topic, found a consensus, and produced a list of relevant criteria.

Association between morphologic grading and implantation rate of Euploid blastocyst

BACKGROUND

Standard morphologic evaluation has been the most widely adopted approach to embryo selection, and remains the most common strategy.The objective of the study to determine the association between the morphologic grading and implantation rate of euploid blastocysts in single frozen-thawed embryo transfer (SET) cycles.

METHODS

A total of 271 patients aged 20-40 years undergoing euploid SET from January 2017 to December 2019 were included in retrospective cohort study.The cycles were divided into three groups based on their morphologic grading before cryopreservation: good-quality (n = 58), average-quality (n = 88) and poor-quality blastocysts (n = 125). The pregnancy outcome of the three morphologic groups were analyzed and a logistic regression of implantation rate was conducted.

RESULTS

Good-quality blastocysts yielded statistically significantly higher implantation rates than poor-quality (79.31% vs. 48%; P<0.001). Planned subgroup analyses by age and the day of TE biopsy were conducted. Logistic regression analyses that adjusted for these variables identified higher implantation rates (adjusted odds ratio(aOR) = 4.083, 95% confidence interval (CI):1.836-9.082, P<0.001) for the good-quality blastocysts than for those that underwent poor-quality cycles in women aged < 35 years, but not in women aged ≥35 years (aOR = 6.074, 95% CI: 0.456-80.919, P = 0.172). The implantation rates were higher among women with good-quality blastocysts on both Day 5 and Day 6 of TE biopsy than among those with poor-quality blastocysts (Day 5, aOR = 3.294, 95% CI:1.260-8.616, P = 0.015; Day 6, aOR = 4.179, 95% CI:1.004 ~ 17.399, P = 0.049). Day 5 euploid blastocysts had no significant difference in implantation potential and early spontaneous abortion rate compared with similarly graded Day 6 euploid blastocysts.

CONCLUSIONS

Blastocyst morphologic grading was associated with implantation rate for euploid embryo transfers after adjustment for potential confounders. These findings suggest that evaluating blastocyst morphology is critical when selecting the best euploid blastocyst.

Preimplantation Genetic Testing for Aneuploidy - a Castle Built on Sand

Preimplantation genetic testing for aneuploidy (PGT-A) has become a routine add-on for in vitro fertilization (IVF) to determine whether human embryos are to be clinically utilized or disposed of. Studies claiming IVF outcome improvements following PGT-A, however, used highly selected patient populations or inappropriate statistical methodologies. PGT-A was never clinically validated in its ability to define a human embryo as chromosomal normal, mosaic, or aneuploid, nor certified by a regulatory body, or an authoritative professional organization. Because of a high false-positive rate, PGT-A, actually reduces live IVF birth chances for many patients. Furthermore, in recent studies the PGT-A hypothesis was demonstrated to be mistaken for biological, mathematical and technical reasons. PGT-A, therefore, should clinically only be offered within experimental study frameworks.

The dawn of the future: 30 years from the first biopsy of a human embryo. The detailed history of an ongoing revolution

Following early studies showing no adverse effects, cleavage stage biopsy by zona drilling using acid Tyrode's solution, and removal of single blastomeres for preimplantation genetic testing (PGT) and identification of sex in couples at risk of X-linked disease, was performed by Handyside and colleagues in late 1989, and pregnancies reported in 1990. This method was later used for specific diagnosis of monogenic conditions, and a few years later also for chromosomal structural and/or numerical impairments, thereby establishing a valuable alternative option to prenatal diagnosis. This revolutionary approach in clinical embryology spread worldwide, and several other embryo biopsy strategies developed over three decades in a process that is still ongoing. The rationale of this narrative review is to outline the different biopsy approaches implemented across the years in the workflow of the IVF clinics that provided PGT: their establishment, the first clinical experiences, their downsides, evolution, improvement and standardization. The history ends with a glimpse of the future: minimally/non-invasive PGT and experimental embryo micromanipulation protocols. This grand theme review outlines a timeline of the evolution of embryo biopsy protocols, whose implementation is increasing worldwide together with the increasing application of PGT techniques in IVF. It represents a vade mecum especially for the past, present and upcoming operators and experts in this field to (re)live this history from its dawn to its most likely future.

Multicenter prospective study of concordance between embryonic cell-free DNA and trophectoderm biopsies from 1301 human blastocysts

BACKGROUND

The recent identification of embryonic cell-free DNA in spent blastocyst media has opened a new era of possibilities for noninvasive embryo aneuploidy testing in assisted reproductive technologies. Yet, previous studies assessing a limited number of embryos reported variable concordance between embryonic cell-free DNA and trophectoderm biopsies, thus questioning the validity of this approach.

OBJECTIVE

This study aimed to evaluate the concordance and reproducibility of testing embryonic cell-free DNA vs trophectoderm DNA obtained from the same embryo in a large sample of human blastocysts and to assess the contribution of the inner cell mass and trophectoderm to embryonic cell-free DNA released to the culture media.

STUDY DESIGN

This is an interim analysis of a prospective, observational study among 8 in vitro fertilization centers in 4 continents to assess consistency between noninvasive embryo aneuploidy testing of embryonic cell-free DNA and conventional trophectoderm biopsy. The analysis included 1301 day-6/7 blastocysts obtained in 406 in vitro fertilization cycles from 371 patients aged 20-44 years undergoing preimplantation genetic testing for aneuploidy. Fresh oocytes underwent intracytoplasmic sperm injection or in vitro fertilization. No previous assisted hatching or vitrification was allowed before media collection. Individual spent blastocyst medium was collected from embryos cultured at least 40 hours from day 4. After media collection, conventional preimplantation genetic testing for aneuploidy, comprising trophectoderm biopsy and blastocyst vitrification, was performed. Embryonic cell-free DNA was analyzed blindly after embryo transfer. Inner cell mass and trophectoderm biopsies were also performed in a subset of 81 aneuploid blastocysts donated for research.

RESULTS

Embryonic cell-free DNA analyses were 78.2% (866/1108) concordant with the corresponding trophectoderm biopsies. No significant differences were detected among centers ranging from 72.5% to 86.3%. Concordance rates exceeded 86% when all defined steps in the culture laboratory were controlled to minimize the impact of maternal and operator contamination. Sensitivity per center ranged from 76.5% to 91.3% and specificity from 64.7% to 93.3%. The false-negative rate was 8.3% (92/1108), and false-positive rate was 12.4% (137/1108). The 2 fertilization techniques provided similar sensitivity (80.9% vs 87.9%) and specificity (78.6% vs 69.9%). Multivariate analysis did not reveal any bias from patient clinical background, ovarian stimulation protocols, culture conditions, or embryo quality on testing accuracy of concordance. Moreover, concordances of embryonic cell-free DNA with trophectoderm and inner cell mass suggest that the embryonic cell-free DNA originates from both compartments of the human embryo.

CONCLUSION

Noninvasive analysis of embryonic cell-free DNA in spent blastocyst culture media demonstrates high concordance with trophectoderm biopsy results in this large multicenter series. A noninvasive approach for prioritizing embryo euploidy offers important advantages such as avoiding invasive embryo biopsy and decreased cost, potentially increasing accessibility for a wider patient population.

Necessity is the mother of invention and the evolutionary force driving the success of in vitro fertilization

During the last few decades, millions of healthy children have been born with the aid of in vitro fertilization (IVF). This success belies the fact that IVF treatment is comprised of a complex series of interventions starting with a customized control ovarian stimulation protocol. This is followed by the induction of oocyte maturation, the retrieval of mature oocytes and in vitro fertilization, which often involves the microinjection of a single sperm into the oocyte. After fertilization, the resulting embryos are cultured for up to 7 days. The best embryos are transferred into the uterus where the embryo implants and hopefully develops into a healthy child. However, frequently the best embryos are biopsied and frozen. The biopsied cells are analyzed to identify those embryos without chromosomal abnormalities. These embryos are eventually thawed and transferred with pregnancy rates as good if not better than embryos that are not biopsied and transferred in a fresh cycle. Thus, IVF treatment requires the coordinated efforts of physicians, nurses, molecular biologists and embryologists to conduct each of these multifaceted phases in a seamless and flawless manner. Even though complex, IVF treatment may seem routine today, but it was not always the case. In this review the evolution of human IVF is presented as a series of innovations that resolved a technical hurdle in one component of IVF while creating challenges that eventually lead to the next major advancement. This step-by-step evolution in the treatment of human infertility is recounted in this review.

Preimplantation Genetic Testing: Where We Are Today

Background: Preimplantation genetic testing (PGT) is widely used today in in-vitro fertilization (IVF) centers over the world for selecting euploid embryos for transfer and to improve clinical outcomes in terms of embryo implantation, clinical pregnancy, and live birth rates. Methods: We report the current knowledge concerning these procedures and the results from different clinical indications in which PGT is commonly applied. Results: This paper illustrates different molecular techniques used for this purpose and the clinical significance of the different oocyte and embryo stage (polar bodies, cleavage embryo, and blastocyst) at which it is possible to perform sampling biopsies for PGT. Finally, genetic origin and clinical significance of embryo mosaicism are illustrated. Conclusions: The preimplantation genetic testing is a valid technique to evaluated embryo euploidy and mosaicism before transfer.

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.

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.

Incidence, Origin, and Predictive Model for the Detection and Clinical Management of Segmental Aneuploidies in Human Embryos

Despite next-generation sequencing, which now allows for the accurate detection of segmental aneuploidies from in vitro fertilization embryo biopsies, the origin and characteristics of these aneuploidies are still relatively unknown. Using a multifocal biopsy approach (four trophectoderms [TEs] and one inner cell mass [ICM] analyzed per blastocyst; n = 390), we determine the origin of the aneuploidy and the diagnostic predictive value of segmental aneuploidy detection in TE biopsies toward the ICM's chromosomal constitution. Contrary to the prevalent meiotic origin of whole-chromosome aneuploidies, we show that sub-chromosomal abnormalities in human blastocysts arise from mitotic errors in around 70% of cases. As a consequence, the positive-predictive value toward ICM configuration was significantly lower for segmental as compared to whole-chromosome aneuploidies (70.8% versus 97.18%, respectively). In order to enhance the clinical utility of reporting segmental findings in clinical TE biopsies, we have developed and clinically verified a risk stratification model based on a second TE biopsy confirmation and segmental length; this model can significantly improve the prediction of aneuploidy risk in the ICM in over 86% of clinical cases enrolled. In conclusion, we provide evidence of the predominant mitotic origin of segmental aneuploidies in preimplantation embryos and develop a risk stratification model that can help post-test genetic counseling and that facilitates the decision-making process on clinical utilization of these embryos.