Trophectoderm biopsy protocols may impact the rate of mosaic blastocysts in cycles with pre-implantation genetic testing for aneuploidy

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

BACKGROUND

To evaluate whether increasing total gonadotropin (Gn) dose is associated with changes in euploid blastocyst rate in preimplantation genetic testing (PGT) oocytes.

METHODS

This retrospective cohort study was conducted between 2017 and 2022, and 19,246 oocytes were grouped and analyzed based on tri-sectional quantiles of total Gn doses.

SETTING

Single reproductive medical center.

SUBJECTS

All the patients who underwent PGT cycles, including PGT for aneuploidy, monogenic disorders, and structural rearrangements, were included.

EXPOSURE

Next-generation sequencing platforms for chromosomal analysis.

MAIN OUTCOME MEASURES

Blastocyst formation and euploid blastocyst rates.

RESULTS

In total, 19,246 oocytes and 5375 PGT blastocysts were analyzed. There were significant differences in blastocyst formation and euploid blastocyst rates among the groups classified according to tri-sectional quantiles of total Gn doses. Significant differences in age, body mass index (BMI), proportion of primary infertility, anti-Müllerian hormone (AMH) levels, number of oocytes retrieved, controlled ovarian stimulation (COS) regimen, type of Gn, and PGT category were observed among the three groups. After stratifying the analysis by age, BMI, infertility diagnosis, AMH levels, number of oocytes retrieved, PGT category, type of Gn, and COS regimen, significant differences were only seen in a small number of specific subgroups. Furthermore, the results of the multiple logistic regression analysis showed that the blastocyst formation and euploid blastocyst rates did not significantly increase or decrease with the total Gn dose, whether treated as a continuous variable or divided into three Gn groups as categorical variables. Notably, advancing age was a risk factor for blastocyst formation and euploid blastocyst rates. PGT for structural rearrangements was a risk factor for blastocyst formation and euploid blastocyst rates as compared with PGT for aneuploidy.

CONCLUSION

In the total PGT cycles, advancing age, and preimplantation genetic testing for structural rearrangements negatively affected blastocyst formation and euploid blastocyst rates; however, the total Gn dose did not affect blastocyst formation and euploid blastocyst rates.

Beyond black-box models: explainable AI for embryo ploidy prediction and patient-centric consultation

PURPOSE

To determine if an explainable artificial intelligence (XAI) model enhances the accuracy and transparency of predicting embryo ploidy status based on embryonic characteristics and clinical data.

METHODS

This retrospective study utilized a dataset of 1908 blastocyst embryos. The dataset includes ploidy status, morphokinetic features, morphology grades, and 11 clinical variables. Six machine learning (ML) models including Random Forest (RF), Linear Discriminant Analysis (LDA), Logistic Regression (LR), Support Vector Machine (SVM), AdaBoost (ADA), and Light Gradient-Boosting Machine (LGBM) were trained to predict ploidy status probabilities across three distinct datasets: high-grade embryos (HGE, n = 1107), low-grade embryos (LGE, n = 364), and all-grade embryos (AGE, n = 1471). The model's performance was interpreted using XAI, including SHapley Additive exPlanations (SHAP) and Local Interpretable Model-agnostic Explanations (LIME) techniques.

RESULTS

The mean maternal age was 38.5 ± 3.85 years. The Random Forest (RF) model exhibited superior performance compared to the other five ML models, achieving an accuracy of 0.749 and an AUC of 0.808 for AGE. In the external test set, the RF model achieved an accuracy of 0.714 and an AUC of 0.750 (95% CI, 0.702-0.796). SHAP's feature impact analysis highlighted that maternal age, paternal age, time to blastocyst (tB), and day 5 morphology grade significantly impacted the predictive model. In addition, LIME offered specific case-ploidy prediction probabilities, revealing the model's assigned values for each variable within a finite range.

CONCLUSION

The model highlights the potential of using XAI algorithms to enhance ploidy prediction, optimize embryo selection as patient-centric consultation, and provides reliability and transparent insights into the decision-making process.

A healthy live birth after mosaic blastocyst transfer in preimplantation genetic testing for GATA1-related cytopenia combined with HLA matching

BACKGROUND

GATA1-related cytopenia (GRC) is characterized by thrombocytopaenia and/or anaemia ranging from mild to severe. Haematopoietic stem cell transplantation (HSCT) is a healing therapeutic choice for GRC patients. We identified a novel pathogenic variant (GATA1: c.1019delG) in a boy with GATA1-related cytopenia. Then we performed preimplantation genetic testing (PGT) in this GRC family. After a mosaic embryo transfered, a healthy and HLA-compatible with the proband baby was delivered.

CASE PRESENTATION

The proband is a 6-year-old boy who was diagnosed to have transfusion-dependent anaemia since 3 year old. Whole-exome sequencing (WES) showed that the proband has a hemizygous variant c.1019delG in GATA1, which is inherited from his mother. His parents decided to undergo PGT to have a health and HLA-compatible offspring. After whole genome amplification (WGA) of biopsied trophectoderm (TE) cells, next generation sequencing (NGS)-based PGT was preformed to analyse embryos on chromosomal aneuploidy, target mutation and HLA typing. There were 3 embryos HLA-matched to the proband. The genotypes of the 3 embryos were heterozygous variant, hemizygous variant, normal respectively. After a heterozygous, mosaic partial trisomy (chr)16, and HLA-matched embryo transfer, a healthy baby was delivered and whose HSCT is compatible with the proband.

CONCLUSIONS

NGS-based PGT-HLA is a valuable procedure for the treatment of GATA1-related cytopenia caused by GATA1 variants, or other haematological disorders, oncological and immunological diseases. Furthermore, our study reconfirms that mosaic embryos transfer would bring healthy offspring.

Evaluating the developmental potential of 2.1PN-derived embryos and associated chromosomal analysis

PURPOSE

Zygotes with 2.1 pronuclei (2.1PN) present with two normal-sized pronuclei, and an additional smaller pronucleus, that is approximately smaller than two thirds the size of a normal pronucleus. It remains unclear whether the additional pronucleus causes embryonic chromosome abnormalities. In the majority of cases, in vitro fertilization (IVF) clinics discarded 2.1PN zygotes. Thus, the present study aimed to evaluate the developmental potential and value of 2.1PN zygotes.

METHODS

2.1PN-derived embryos from 164 patients who underwent IVF or intracytoplasmic sperm injection (ICSI) treatment between January 2021 and December 2022 were included in the present study. All embryos were monitored using a time-lapse system, and blastocyst formation was used to assess 2.1PN-derived embryo developmental potential. The blastocyst formation was quantified using generalized estimating equations, and chromosome euploidy was analyzed using next-generation sequencing (NGS). In addition, the potential association between age and occurrence of 2.1PN zygotes was determined.

RESULTS

The present study demonstrated that numerous 2.1PN zygotes developed into blastocysts. Early cleavage patterns and embryo quality on Day 3 were the independent predictors for the blastocyst formation of 2.1PN-derived embryos. The 2.1PN zygotes displayed a comparable developmental potential compared to 2PN zygotes in advanced age patients (≥ 38). Moreover, there was a tendency that 2.1PN-derived blastocysts showed a similar euploidy rate compared to 2PN-derived blastocysts.

CONCLUSION

Clinicians should consider using 2.1PN-derived euploid embryos for transfer after preimplantation genetic testing in the absence of available 2PN embryo cycles. 2.1PN-derived embryos could be a candidate, particularly beneficial for patients at advanced age.

Factors Associated With Mosaicism in Human Embryos: A Retrospective Study

Objective This study aims to identify factors associated with mosaicism in human embryos at Hung Vuong Hospital. Methods We performed a retrospective analysis of data from 2018 to 2022, approved by the Hung Vuong Hospital Ethics Committee (CS/HV/23/15). We analyzed variables such as demographic characteristics, clinical measurements, and in-vitro fertilization (IVF) cycle outcomes to investigate their relationship with embryo mosaicism. Results A total of 73 couples undergoing IVF with preimplantation genetic testing (PGT) were included in the analysis. Among 308 embryos, 98 (31.8%) were mosaic, 124 (40.3%) were euploid, and 86 (27.9%) were aneuploid. Univariable analysis revealed that female age was significantly associated with increased odds of mosaicism (odd ratio (OR) = 1.11, 95% confidence interval (CI): 1.04 - 1.19, p = 0.003). Male age demonstrated a marginal association with mosaicism (OR = 1.05, 95% CI: 1.00 - 1.11, p = 0.07). Other factors, including body mass index (BMI), anti-Mullerian hormone (AMH) levels, blood types, and sperm quality, were not significantly associated with mosaicism. In the multivariable analysis, controlling for both female and male age, female age showed a trend toward significance (OR = 1.12, 95% CI: 1.02 - 1.23, p = 0.02), while male age showed no significant effect (OR = 0.99, 95% CI: 0.92 - 1.06, p = 0.75). Conclusions The findings suggest that female age is a critical factor influencing the occurrence of mosaicism in embryos. Further research is needed to fully understand the mechanisms underlying mosaicism in human embryos.

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.

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.

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.

PGT-A mosaicism based on NGS intermediate copy numbers: is it time to stop reporting them?

Mosaicism represents a genuine real phenomenon, but its high prevalence and undisclosed clinical significance, stress the burden on genetic counseling and the management of PGT-A results. Even though the assumption of mosaicism from NGS intermediate chromosome copy number profiles may represent a reasonable interpretation, other potential technical reasons, including amplification bias, contamination, biopsy technique, or the analysis algorithms, may constitute alternative explanations. Thresholds confining mosaicism ranges are established according to models employing mixtures of normal and abnormal cells with steady conditions of quantity and quality which are unable to reflect the full extent of variability present in a trophectoderm (TE) biopsy specimen. When the concordance of TE with the ICM is considered, mosaic TE biopsies poorly correlate with the chromosomal status of the remaining embryo, displaying mostly ICM aneuploidy in cases of TE high-range mosaics diagnosis and euploidy when mosaicism grade in TE is less than 50% (low-mid range mosaicism), which implies an evident overestimation of mosaicism results. Indeed, a binary classification of NGS profiles that excludes mosaic ranges, including only euploid and aneuploid diagnosis, provides higher specificity and accuracy in identifying abnormal embryos and discarding them. As intermediate copy number profiles do not represent strong evidence of mosaicism but only an inaccurate and misleading assumption, and considering that no increased risk has been reported in the offspring, until diagnosis specificity is improved and its clinical implications are determined, laboratories should consider limiting predictions to euploid and aneuploid and stop reporting mosaicism.

Reproductive outcomes with delayed blastocyst development: the clinical value of day 7 euploid blastocysts in frozen embryo transfer cycles

Embryos of optimal development reach blastocyst stage 116 ± 2 h after insemination. Usable D7 blastocysts represent nearly 5% of embryos in IVF with acceptable pregnancy and live birth rates, however data are still limited. Therefore, this study aimed to analyze the ongoing pregnancy rate (OPR) of D7 blastocysts in single euploid frozen embryo transfer (FET) cycles. An observational study was performed including 1527 FET cycles with blastocysts biopsied on D5 (N = 855), D6 (N = 636) and D7 (N = 36). Blastocysts were classified as good (AA/AB/BA), fair (BB) or poor (AC/BC/CC/CA/CB) (Gardner scoring). FETs were performed in natural cycles (NC) or hormone replacement therapy (HRT) cycles. Patient's age differed significantly between D5, D6 and D7 blastocysts FET cycles (33.2 ± 5.6, 34.4 ± 5.3 and 35.9 ± 5.2, P < 0.001). OPRs were higher when D5 euploid blastocysts were transferred compared with D6 and D7 (56.0% vs. 45.3% and 11.1%, P < 0.001). Poor quality blastocysts were predominant in D7 blastocyst FET cycles (good quality: 35.4%, 27.2%, 5.6%; fair quality: 52.1%, 38.5%, 11.1%; poor quality: 12.5%, 34.3%, 83.3%, P < 0.001 for D5, D6 and D7 blastocysts; respectively). OPR was significantly reduced by D7 blastocyst FETs (OR = 0.23 [0.08;0.62], P = 0.004), patient's BMI (OR = 0.96 [0.94;0.98], P < 0.001), HRT cycles (OR = 0.70 [0.56;0.88], P = 0.002) and poor quality blastocysts (OR = 0.33 [0.24;0.45], P < 0.001). OPR is significantly reduced with D7 compared with D5/D6 euploid blastocysts in FET cycles. The older the patient, the more likely they are to have an FET cycle with blastocysts biopsied on D7, therefore culturing embryos until D7 can be a strategy to increase OPR outcomes in patients ≥38 years.

A novel embryo biopsy morphological analysis and genetic integrality criterion system significantly improves the outcome of preimplantation genetic testing

PURPOSE

While efforts have been made to establish blastocyst grading systems in the past decades, little research has examined the quality of biopsy specimens. This study is the first to correlate the morphology of biopsied trophectoderm (TE) cells to their quality and subsequent genetic testing results of preimplantation genetic testing (PGT), through an innovative Morphological Analysis and Genetic Integrality Criterion (MAGIC) system.

METHODS

Biopsied TE cells were first evaluated according to the MAGIC procedure, followed by whole-genome amplification (WGA) and library construction, and then sequenced using the Illumina X Ten Platform. Copy number variation (CNV) and allele drop-out (ADO) rates as well as test failure rates were compared and analyzed.

RESULTS

Our data explores the relationship between TE cell morphology and its quality and final genetic testing outcome, which is established based on the MAGIC system. MAGIC guarantees that only high- or good-quality TE cells are used for genetic testing to generate excellent data uniformity and lower ADO rates. Low-quality cells containing biopsied TE cell mass are responsible for the "background noise" of CNV analysis.

CONCLUSION

The MAGIC application has effectively decreased the false-positive mosaicism, hence to ensure the stability and veracity of detection results, to avoid misdiagnoses, and to improve accuracy, as well as to avoid re-biopsy procedures. The study also contributes to understand how the IVF laboratory and the molecular biology laboratory depend on each other to achieve good-quality PGT results, which are clinically relevant for the patients.

Opening the black box: why do euploid blastocysts fail to implant? A systematic review and meta-analysis

BACKGROUND

A normal chromosomal constitution defined through PGT-A assessing all chromosomes on trophectoderm (TE) biopsies represents the strongest predictor of embryo implantation. Yet, its positive predictive value is not higher than 50-60%. This gap of knowledge on the causes of euploid blastocysts' reproductive failure is known as 'the black box of implantation'.

OBJECTIVE AND RATIONALE

Several embryonic, maternal, paternal, clinical, and IVF laboratory features were scrutinized for their putative association with reproductive success or implantation failure of euploid blastocysts.

SEARCH METHODS

A systematic bibliographical search was conducted without temporal limits up to August 2021. The keywords were '(blastocyst OR day5 embryo OR day6 embryo OR day7 embryo) AND (euploid OR chromosomally normal OR preimplantation genetic testing) AND (implantation OR implantation failure OR miscarriage OR abortion OR live birth OR biochemical pregnancy OR recurrent implantation failure)'. Overall, 1608 items were identified and screened. We included all prospective or retrospective clinical studies and randomized-controlled-trials (RCTs) that assessed any feature associated with live-birth rates (LBR) and/or miscarriage rates (MR) among non-mosaic euploid blastocyst transfer after TE biopsy and PGT-A. In total, 41 reviews and 372 papers were selected, clustered according to a common focus, and thoroughly reviewed. The PRISMA guideline was followed, the PICO model was adopted, and ROBINS-I and ROB 2.0 scoring were used to assess putative bias. Bias across studies regarding the LBR was also assessed using visual inspection of funnel plots and the trim and fill method. Categorical data were combined with a pooled-OR. The random-effect model was used to conduct the meta-analysis. Between-study heterogeneity was addressed using I2. Whenever not suitable for the meta-analysis, the included studies were simply described for their results. The study protocol was registered at http://www.crd.york.ac.uk/PROSPERO/ (registration number CRD42021275329).

OUTCOMES

We included 372 original papers (335 retrospective studies, 30 prospective studies and 7 RCTs) and 41 reviews. However, most of the studies were retrospective, or characterized by small sample sizes, thus prone to bias, which reduces the quality of the evidence to low or very low. Reduced inner cell mass (7 studies, OR: 0.37, 95% CI: 0.27-0.52, I2 = 53%), or TE quality (9 studies, OR: 0.53, 95% CI: 0.43-0.67, I2 = 70%), overall blastocyst quality worse than Gardner's BB-grade (8 studies, OR: 0.40, 95% CI: 0.24-0.67, I2 = 83%), developmental delay (18 studies, OR: 0.56, 95% CI: 0.49-0.63, I2 = 47%), and (by qualitative analysis) some morphodynamic abnormalities pinpointed through time-lapse microscopy (abnormal cleavage patterns, spontaneous blastocyst collapse, longer time of morula formation I, time of blastulation (tB), and duration of blastulation) were all associated with poorer reproductive outcomes. Slightly lower LBR, even in the context of PGT-A, was reported among women ≥38 years (7 studies, OR: 0.87, 95% CI: 0.75-1.00, I2 = 31%), while obesity was associated with both lower LBR (2 studies, OR: 0.66, 95% CI: 0.55-0.79, I2 = 0%) and higher MR (2 studies, OR: 1.8, 95% CI: 1.08-2.99, I2 = 52%). The experience of previous repeated implantation failures (RIF) was also associated with lower LBR (3 studies, OR: 0.72, 95% CI: 0.55-0.93, I2 = 0%). By qualitative analysis, among hormonal assessments, only abnormal progesterone levels prior to transfer were associated with LBR and MR after PGT-A. Among the clinical protocols used, vitrified-warmed embryo transfer was more effective than fresh transfer (2 studies, OR: 1.56, 95% CI: 1.05-2.33, I2 = 23%) after PGT-A. Lastly, multiple vitrification-warming cycles (2 studies, OR: 0.41, 95% CI: 0.22-0.77, I2 = 50%) or (by qualitative analysis) a high number of cells biopsied may slightly reduce the LBR, while simultaneous zona-pellucida opening and TE biopsy allowed better results than the Day 3 hatching-based protocol (3 studies, OR: 1.41, 95% CI: 1.18-1.69, I2 = 0%).

WIDER IMPLICATIONS

Embryo selection aims at shortening the time-to-pregnancy, while minimizing the reproductive risks. Knowing which features are associated with the reproductive competence of euploid blastocysts is therefore critical to define, implement, and validate safer and more efficient clinical workflows. Future research should be directed towards: (i) systematic investigations of the mechanisms involved in reproductive aging beyond de novo chromosomal abnormalities, and how lifestyle and nutrition may accelerate or exacerbate their consequences; (ii) improved evaluation of the uterine and blastocyst-endometrial dialogue, both of which represent black boxes themselves; (iii) standardization/automation of embryo assessment and IVF protocols; (iv) additional invasive or preferably non-invasive tools for embryo selection. Only by filling these gaps we may finally crack the riddle behind 'the black box of implantation'.

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

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

On the origins and fate of chromosomal abnormalities in human preimplantation embryos: an unsolved riddle

About 8 out of 10 human embryos obtained in vitro harbour chromosomal abnormalities of either meiotic or mitotic origin. Abnormalities of mitotic origin lead to chromosomal mosaicism, a phenomenon which has sparked much debate lately as it confounds results obtained through preimplantation genetic testing for aneuploidy (PGT-A). PGT-A in itself is still highly debated, not only on the modalities of its execution, but also on whether it should be offered to patients at all.

We will focus on post-zygotic chromosomal abnormalities leading to mosaicism. First, we will summarize what is known of the rates of chromosomal abnormalities at different developmental stages. Next, based on the current understanding of the origin and cellular consequences of chromosomal abnormalities, which is largely based on studies on cancer cells and model organisms, we will offer a number of hypotheses on which mechanisms may be at work in early human development. Finally, and very briefly, we will touch upon the impact our current knowledge has on the practice of PGT-A. What is the level of abnormal cells that an embryo can tolerate before it loses its potential for full development? And is blastocyst biopsy as harmless as it seems?

Accumulation of Cleavage-Stage Embryos by Vitrification may Compromise Embryonic Developmental Potential in Preimplantation Genetic Testing

It was suggested that the embryo pooling was an alternative for patients with insufficient number of embryos for preimplantation genetic testing (PGT) in a single ovarian stimulation cycle. However, limited study noticed whether it is an efficient strategy to pool cleavage-stage embryos by vitrification. This study included 71 cycles with vitrified-warmed and fresh embryos simultaneously for PGT between May 2016 and May 2021. The embryos from the same patients were split into two groups based on the origin: warming group and fresh group. Embryo development, sequencing results, clinical and neonatal outcomes were compared. The results showed that the rate of high-quality embryos in the warming group was significantly higher than that in the fresh group (64.53% versus 52.61%, P = 0.011); however, the available blastocyst rate in this group was significantly lower than that in the fresh group (47.29% versus 57.83%, P = 0.026). There were 96 and 144 blastocysts that underwent trophectoderm (TE) biopsy in warming and fresh groups, respectively. The high-quality blastocyst rate was significantly lower in the warming group compared to the fresh group (57.29% versus 70.14%, P = 0.041). The rates of genetic transferable blastocyst were comparable between the two groups (P = 0.956). There were no statistical differences in terms of embryo implantation, clinical pregnancy, miscarriage rates, and neonatal outcomes between the two groups. In conclusion, this study demonstrated that the cleavage-stage embryo pooling strategy might be unfavorable for the maintenance of embryonic development potential. If not necessary, it is not recommended to pool cleavage-stage embryos for PGT.

Application of Two Blastocyst Biopsy Strategies in Preimplantation Genetic Testing Treatment and Assessment of Their Effects

BACKGROUND

Blastocyst biopsy has become the most mainstream biopsy method. Currently, there are two blastocyst biopsy strategies. Many studies have compared the advantages and disadvantages between blastomere and blastocyst biopsy, but fewer articles have compared the two blastocyst biopsy strategies. For the moment, no published studies have explored the entire set of information on embryo development, next-generation sequencing results, and clinical outcomes, including the baby's health status with the two blastocyst biopsy strategies.

METHODS

A total of 323 preimplantation genetic testing cycles from April 2018 to May 2020, including 178 cycles with Strategy A and 145 cycles with Strategy B. Strategy A was to create a laser-assisted zona pellucid opening for cleavage embryo on the third day after insemination, but Strategy B was not. Strategy A performed a biopsy for artificially assisted hatching blastocysts, while Strategy B performed a biopsy for expanded blastocysts on day 5 or 6. In this study, embryo development, next-generation sequencing results, pregnancy outcomes, and offspring health of the two strategies were compared and analyzed.

RESULTS

There were no statistical differences between the two groups in the rate of fertilization, blastocyst and abortion. The rate of cleavage from Strategy A was slightly higher than Strategy B, and the rate of high-quality cleavage embryo was lower than Strategy B, while the rate of high-quality blastocyst was higher than Strategy B. The rate of no-results blastocyst was significantly lower than Strategy B. In particular, the rate of biochemical pregnancy, clinical pregnancy, and live birth of Strategy A were significantly lower than those of Strategy B. The average Apgar scores of newborns were ≥8 in both groups, and there was no significant difference in average height and weight. In Strategy A, a baby was born with thumb syndactyly, and Strategy B had no congenital disabilities.

CONCLUSIONS

Blastocyst biopsy strategy without laser-assisted zona pellucid drilling on day 3 achieves better clinical treatment effects. Therefore, Strategy B is an optimal treatment regime for PGT.

Non-Assisted Hatching Trophectoderm Biopsy Does Not Increase The Risks of Most Adverse Maternal and Neonatal Outcome and May Be More Practical for Busy Clinics: Evidence From China

OBJECTIVE

This study was conducted in order to investigate whether non-assisted hatching trophectoderm (TE) biopsy increases the risks of adverse perinatal outcomes in livebirths following elective single cryopreserved-thawed blastocyst transfer.

PATIENTS AND METHODS

A total of 5,412 cycles from 4,908 women who achieved singleton livebirths between 2013 and 2019 were included in this retrospective cohort study. All embryos in this study were fertilized by intracytoplasmic sperm injection (ICSI) and cryopreserved through vitrification. The main intervention is to open the zona pellucida (ZP) of day 5/6 blastocyst immediately for biopsy without pre-assisted hatching. The main outcome measures are the common maternal and neonatal outcomes, including hypertensive disorders of pregnancy (HDPs), gestational diabetes mellitus (GDM), abnormal placentation, abnormalities in umbilical cord and amniotic fluid, preterm birth, cesarean section, low birth weight, postpartum hemorrhage, and prolonged hospital stay (both mothers and infants). The generalized estimation equation (GEE) was used to control the effects of repeated measurements. The non-conditional logistic regression model was used to examine the associations between embryo biopsy status and each adverse perinatal event. Given that the selection bias and changes in learning curve might affect the results, we selected 1,086 similar (matching tolerance = 0.01) cycles from the ICSI group via propensity score matching (PSM) for second comparisons and adjustment (conditional logistic regression).

RESULTS

After adjusting for confounders, we confirmed that the non-assisted hatching protocol did not increase the risks of most adverse maternal and neonatal outcomes. Despite this, there were increased risks of GDM (aOR: 1.522, 95% CI: 1.141-2.031) and umbilical cord abnormalities (aOR: 11.539, 95% CI: 1.199-111.067) in the biopsy group. In the second comparisons after PSM, GDM incidence in the biopsy group was still higher (7.26% vs. 5.16%, P = 0.042), yet all measurement outcomes were equally likely to occur in both groups after the second adjustment.

CONCLUSIONS

The non-assisted hatching TE biopsy does not increase the risks of most adverse perinatal outcomes. However, there is a higher GDM incidence in the biopsy group, and this association warrants further study. Considering its safety and simplicity, the non-assisted hatching protocol has the potential to become the preferred option for TE biopsy, especially in busy clinics and IVF laboratories.

Can Culture Media Impact Preimplantation Embryo Aneuploidy?

With continued improvements in blastocyst culture, cell sampling approaches, and genetic analysis platforms, the resulting improvements in embryo development and the resolution and accuracy of chromosome analysis have provided valuable insights into the preimplantation embryo. This includes the impact of in vitro culture conditions on chromosomal dynamics. Specifically, through analysis of embryo aneuploidy and mosaicism, a growing number of reports indicate that rates of chromosomal abnormalities can vary between IVF centers. Because differences in mosaicism reflect mitotic errors, this endpoint analysis suggests that IVF laboratory-controlled variables during embryo development may be influencing chromosome separation and segregation. A growing body of literature suggests that culture media may be one variable influencing preimplantation embryo aneuploidy and mosaicism. However, these data are far from definitive in demonstrating cause-and-effect. Whether reported differences may be due to media formulation, use of sequential media or single-step media, or uninterrupted culture approaches is unknown. Importantly, variables directly impacting media performance and embryo development, including pH, temperature, osmolality, and oxygen concentration, must also be considered and make it difficult to isolate the impact of culture media as the sole factor responsible. These IVF laboratory variables will be reviewed and literature suggesting a possible link to mitotic aneuploidy/mosaicism will be discussed.

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

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