Abnormally fertilized oocytes can result in healthy live births: improved genetic technologies for preimplantation genetic testing can be used to rescue viable embryos in in vitro fertilization cycles

An expert opinion on rescuing atypically pronucleated human zygotes by molecular genetic fertilization checks in IVF

IVF laboratories routinely adopt morphological pronuclear assessment at the zygote stage to identify abnormally fertilized embryos deemed unsuitable for clinical use. In essence, this is a pseudo-genetic test for ploidy motivated by the notion that biparental diploidy is required for normal human life and abnormal ploidy will lead to either failed implantation, miscarriage, or significant pregnancy complications, including molar pregnancy and chorionic carcinoma. Here, we review the literature associated with ploidy assessment of human embryos derived from zygotes displaying a pronuclear configuration other than the canonical two, and the related pregnancy outcome following transfer. We highlight that pronuclear assessment, although associated with aberrant ploidy outcomes, has a low specificity in the prediction of abnormal ploidy status in the developing embryo, while embryos deemed abnormally fertilized can yield healthy pregnancies. Therefore, this universal strategy of pronuclear assessment invariably leads to incorrect classification of over 50% of blastocysts derived from atypically pronucleated zygotes, and the systematic disposal of potentially viable embryos in IVF. To overcome this limitation of current practice, we discuss the new preimplantation genetic testing technologies that enable accurate identification of the ploidy status of preimplantation embryos and suggest a progress from morphology-based checks to molecular fertilization check as the new gold standard. This alternative molecular fertilization checking represents a possible non-incremental and controversy-free improvement to live birth rates in IVF as it adds to the pool of viable embryos available for transfer. This is especially important for the purposes of 'family building' or for poor-prognosis IVF patients where embryo numbers are often limited.

Preconception carrier screening and preimplantation genetic testing in the infertility management

BACKGROUND

Genetic testing serves as a valuable element of reproductive care, applicable at various stages of the reproductive journey: (i) before pregnancy, when a couple's genetic reproductive risk can be evaluated; (ii) before embryo implantation, as part of in vitro fertilization (IVF) treatment, to ascertain several inherited or de novo genetic/chromosomal diseases of the embryo before transfer; (iii) during the prenatal period, to assess the genetic costitution of the fetus. Preconception carrier screening (CS) is a genetic test typically performed on couples planning a pregnancy. The primary purpose of CS is to identify couples at-risk of conceiving a child affected by a severe genetic disorder with autosomal recessive or X-linked inheritance. Detection of high reproductive risk through CS allows prospective parents to be informed of their predisposition and improve reproductive decision-making. These include undergoing IVF with preimplantation genetic testing (PGT) or donor gametes, prenatal diagnosis, adoption, remaining childless, taking no actions. Both the presence of the affected gene (PGT-M) and chromosomal status (PGT-A) of the embryo can be comprehensively assessed through modern approaches.

OBJECTIVES

We provide a review of CS and PGT applications to equip healthcare providers with up-to-date information regarding their opportunities and complexities.

RESULTS AND DISCUSSION

The use of CS and PGT is currently considered the most effective intervention for avoiding both an affected pregnancy whilst using autologous gametes in couples with known increased risk, and chromosomal abnormalities. As our understanding in the genetic component in pathological conditions increases, the number of tested disorders will expand, offering a more thorough assessment of one's genetic inheritance. Nevertheless, implementation and development in this field must be accompanied by scientific and ethical considerations to ensure this approach serves the best long-term interests of individuals and society, promoting justice and autonomy and preserving parenthood and the healthcare system.

CONCLUSION

The combination of CS and PGT aligns with principles of personalized medicine by offering reproductive care tailored to the individual's genetic makeup.

Birth of Thirty-Two Healthy Babies Following Transfer of Fresh and Frozen-Thawed Embryos Derived from Monopronuclear Zygotes: A Retrospective Study

Background and Objectives: Fertilized zygotes normally display two pronuclei (PN), but abnormal fertilization patterns (0, 1 or >2PN) are observed daily in IVF labs. Multiple PN zygotes (>2) are generally discarded due to an increased risk of aneuploidy. However, the decision to transfer or not transfer 1PN-derived embryos remains controversial. The aims of our study were to analyze the neonatal outcomes of fresh or frozen-thawed embryos derived from 1PN zygotes, and to evaluate the influence of the fertilization method. Materials and Methods: Data were retrospectively collected from cycles performed between January 2018 and December 2022. Fresh cycles were analyzed for the comparative fate of 1PN zygotes (n = 1234) following conventional in vitro fertilization (cIVF; n = 648) or intracytoplasmic sperm injection (ICSI; n = 586), as well as the results of the 64 transfers of 1PN-derived embryos (pregnancy rate (PR) and neonatal outcomes). This pregnancy follow-up was also applied to 167 transfers of frozen-thawed 1PN-derived embryos. Results: In fresh cycles, 46% of the 1PN zygotes in the cIVF group developed into embryos of sufficient quality to be transferred or frozen (day 3 or 5/6). This rate was lower in the fresh ICSI cycles (33%). Blastulation rate was also significantly higher in the cIVF group (44%) in comparison to the ICSI group (20%). The fresh single embryo transfers (32 per group) allowed seven pregnancies in the cIVF group (PR = 21.9%) as compared to four pregnancies in the ICSI group (PR = 12.5%). In the cIVF group, five deliveries of healthy newborns were achieved, but only one in the ICSI group. In frozen/thawed cycles, 36 pregnancies were obtained out of the 167 transfers. A non-significant difference was observed between embryos derived from cIVF cycles (PR = 26%) and ICSI cycles (PR = 16%) with 18 and 8 healthy babies born, respectively. Conclusions: We observed better outcomes for 1PN zygotes in cIVF cycles in comparison to ICSI cycles. Our center policy to transfer good-quality 1PN-derived embryos allowed the birth of 32 healthy babies.

The Blastulation Rate Is Negatively Associated With Euploid Rate

OBJECTIVES

To study the association between the blastulation rate, the presence of 1 pronucleus (1PN) zygotes, and the ploidy of the cohort of blastocysts.

METHODS

A cross-sectional study using the existing databases of 2 university fertility centres in Canada. We included 345 cycles from 235 couples who underwent next-generation sequencing preimplantation genetic testing for the detection of aneuploidy in the study.

RESULTS

A total of 1456 blastocysts were biopsied. In multivariate analysis, only female age and the number of 1PN/2PN embryos showed a negative association with euploid ratio. Surprisingly, when the analysis was limited to cycles with no delayed blastulation, the blastulation rate was also negatively associated with the euploid ratio.

CONCLUSIONS

This study sheds some light on the stages of early embryo development. Further study on the mechanisms governing embryo development and the different cell cycle checkpoints in embryo development is warranted.

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.

The utility of human two plus one small pronucleated zygotes (2.1PN) based on clinical outcomes and the focused ploidy analysis

PURPOSE

Are human embryos arising from two plus one small pronucleated zygotes, called 2.1 pronuclei (PN), clinically useful?

METHODS

In a retrospective embryo cohort study and prospective experimental study, a total of 287 cycles in which at least one 2.1PN was identified in the fertilization check were included. Embryonic development and clinical outcome were compared for the 1395 2PN zygotes and 304 2.1PN zygotes that were siblings. All embryos were individually cultured in time-lapse systems. Twenty-five 2.1PN-derived blastocysts, donated for research, were used in focused single-nucleotide variant ploidy analysis to identify the distribution pattern of heterozygosity.

RESULTS

The average diameter of PN was 24.9 ± 2.4 µm for large PN and 10.2 ± 2.4 µm for small PN; 79.9% of small PN was derived from female pronuclei. Blastocyst formation rate and good-quality blastocyst rate were significantly lower with 2.1PN embryos than with 2PN embryos (40.0% vs. 57.7%, 21.4% vs. 33.5%, respectively). A total of 13 embryos derived from 2.1PN were transferred, and three healthy babies were born. In ploidy constitutions of trophectoderm (TE), 2.1PN-derived blastocyst TE was shown to be mostly diploid (95.8%, 23/24), and only one blastocyst showed triploid.

CONCLUSIONS

It was suggested that 2.1PN embryos have lower embryonic developmental potential than 2PN embryos, but most of the 2.1PN were diploid, indicating that they are likely to be clinically usable. It is recommended to perform embryo transfer following a combination of PGT-A and ploidy analysis.

Embryos derived from single pronucleus are suitable for preimplantation genetic testing

OBJECTIVE

To study and compare the preimplantation genetic testing for monogenic disorders (PGT-M) results, and to evaluate the treatment cycle outcomes of embryos derived from a single pronucleus (1PN) vs. two pronuclei (2PN).

DESIGN

A retrospective cohort study from January 2018 to December 2022 involving in vitro fertilization (IVF)-PGT-M treatment cycles.

SETTING

Single, academically affiliated fertility center.

PATIENTS

A total of 244 patients underwent 351 IVF-PGT-M treatment cycles.

INTERVENTION

Embryo biopsy with molecular testing for a monogenic disorder.

MAIN OUTCOME MEASURES

The molecular diagnosis results and clinical outcomes after the transfer of embryos derived from 1PN and 2PN in IVF-PGT-M treatment cycles.

RESULTS

Embryos derived from 1PN have a significantly low developmental potential with a lower rate of embryos that underwent biopsy compared with 2PN-derived embryos; 1PN-derived embryos demonstrated a significantly lower number of blastocysts (24% vs. 37.9%) and top-quality blastocysts (22.3% vs. 48.1%) compared with 2PN-derived embryos. Lower successfully completed and unaffected PGT-M results were achieved in 1PN compared with 2PN-derived embryos (47.1% vs. 65.5% and 18.7% vs. 31.6%, respectively), with significantly higher abnormal molecular results (39.6% vs. 22.7%). The embryo transfer of 24 1PN-derived embryos with no affected genetic disorder resulted in 5 (20.8%) clinical pregnancies and 4 (16.7%) live births (LBs).

CONCLUSIONS

Within the limits of fewer embryos derived from 1PN that yielded unaffected embryos suitable for transfer, the clinical pregnancy and LB rate of 1PN embryos undergoing PGT-M are reassuring. We, therefore, suggest applying PGT-M to embryos derived from 1PN embryos to improve the cumulative clinical pregnancy and LB rates.

How should the best human embryo in vitro be? Current and future challenges for embryo selection

In-vitro fertilization (IVF) aims at overcoming the causes of infertility and lead to a healthy live birth. To maximize IVF efficiency, it is critical to identify and transfer the most competent embryo within a cohort produced by a couple during a cycle. Conventional static embryo morphological assessment involves sequential observations under a light microscope at specific timepoints. The introduction of time-lapse technology enhanced morphological evaluation via the continuous monitoring of embryo preimplantation in vitro development, thereby unveiling features otherwise undetectable via multiple static assessments. Although an association exists, blastocyst morphology poorly predicts chromosomal competence. In fact, the only reliable approach currently available to diagnose the embryonic karyotype is trophectoderm biopsy and comprehensive chromosome testing to assess non-mosaic aneuploidies, namely preimplantation genetic testing for aneuploidies (PGT-A). Lately, the focus is shifting towards the fine-tuning of non-invasive technologies, such as "omic" analyses of waste products of IVF (e.g., spent culture media) and/or artificial intelligence-powered morphologic/morphodynamic evaluations. This review summarizes the main tools currently available to assess (or predict) embryo developmental, chromosomal, and reproductive competence, their strengths, the limitations, and the most probable future challenges.

Effect of ejaculatory abstinence period on fertilization and clinical outcomes in ICSI cycles: a retrospective analysis

RESEARCH QUESTION

Does ejaculatory abstinence impact fertilization outcomes in intracytoplasmic sperm injection (ICSI) cycles in infertile couples?

DESIGN

This single-centre retrospective observational study included 6919 ICSI cycles from 2013 to 2022. The primary outcome was the assessment of oocyte fertilization, measured in terms of the rate of formation of two-pronuclear (2PN), 3PN and 1PN zygotes. Secondary outcomes were blastulation, cumulative positive β-human chorionic gonadotrophin test and clinical pregnancy rates. Relationships between ejaculatory abstinence and fertilization outcomes, and ejaculatory abstinence and clinical outcomes were evaluated with multivariable analysis, including possible confounders.

RESULTS

A positive association was observed between ejaculatory abstinence and semen sample volume (P < 0.001), sperm concentration (P < 0.001) and total motile sperm count (P < 0.001). No association was found between the 1PN zygote rate and ejaculatory abstinence (P = 0.97). Conversely, for each additional day of ejaculatory abstinence, the likelihood of obtaining 2PN zygotes from all inseminated oocytes decreased by 3% [adjusted odds ratio (aOR) 0.97, 95% CI 0.94-0.99], whilst the likelihood of obtaining 3PN zygotes from all inseminated oocytes increased significantly by 14% (aOR 1.14, 95% CI 1.07-1.22). No significant associations were found between ejaculatory abstinence and blastulation, cumulative pregnancy or miscarriage rates.

CONCLUSIONS

A longer ejaculatory abstinence period significantly decreases the rate of 2PN zygotes, and increases the rate of 3PN zygotes without directly affect blastulation and pregnancy rates.

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'.

Healthy live birth following embryo transfer of a blastocyst of tetrapronuclear (4PN) origin: a case report

During IVF treatments, normal fertilization is generally evidenced by the appearance of two pronuclei, one arising from the oocyte and the other from the male gamete. Embryos derived from zygotes with a pronuclei number other than two are assumed to possess a ploidy abnormality and their transfer is usually avoided owing to increased risk of implantation failure, miscarriage, and molar pregnancies. Nonetheless, the inclusion of genotyping data in preimplantation genetic testing has revealed that a normal diploid configuration is possible in embryos deriving from zygotes with an abnormal pronuclei number such as tripronuclear and one pronucleus. Here, we present a one-of-a-kind transfer of a tetrapronuclear-derived embryo that was discovered to be diploid and negative for other whole chromosome or segmental aneuploidies during preimplantation genetic testing using a targeted next-generation sequencing approach. The transfer resulted in the live birth of a healthy infant who is now 4 years old and has no apparent health or developmental impairments.

Clinical outcomes of frozen-thawed blastocysts from zygotes with no or one pronucleus for in vitro fertilization and intracytoplasmic sperm injection cycles

PURPOSE

To investigate the clinical outcomes of in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) cycles using frozen-thawed blastocyst transfers derived from zygotes with no (0PN) or one pronucleus (1PN).

METHODS

This retrospective study included 7084 0PN, 2238 1PN, and 72,266 two pronuclear (2PN) embryos cultured to the blastocyst stage from 19,631 IVF and 12,377 ICSI cycles between March 2018 and December 2021. Developmental potential and clinical outcomes of 0PN, 1PN, and 2PN embryos were analyzed. A total of 290 0PN-, 92 1PN-, and 1906 2PN-derived single frozen-thawed blastocyst transfers were performed. Chromosome euploid rates of 0PN-, 1PN-, and 2PN-derived blastocysts were analyzed by next-generation sequencing. Euploid 0PN- and 1PN-derived blastocysts underwent subsequent Infinium Asian Screening Array gene chip analysis to detect ploidy alterations.

RESULTS

Available blastocyst rates of 0PN and 1PN embryos were significantly lower than those of 2PN embryos in both IVF and ICSI cycles. Single 0PN and 1PN blastocysts transferred in frozen-thawed cycles resulted in a similar clinical pregnancy rate, miscarriage rate, live birth rate, and neonatal outcome to 2PN blastocysts in IVF and ICSI cycles. Genetic analysis showed that euploid rates of 0PN- and 1PN-derived blastocysts used for ICSI cycles were similar to that of 2PN-derived blastocysts.

CONCLUSION

Our study indicated that 0PN- and 1PN-derived blastocysts resulted in similar clinical outcomes to 2PN-derived blastocysts. The 0PN- and 1PN-derived blastocysts from ICSI cycles can be transferred as well as those from IVF cycles when the number of 2PN-derived blastocysts is insufficient.

Assessing the clinical viability of micro 3 pronuclei zygotes

PURPOSE

What is the rate of euploidy and clinical viability of embryos resulting from micro 3 pronuclei zygotes?

METHODS

Retrospective cohort analysis in a single, academic in vitro fertilization (IVF) center from March 2018 to June 2021. Cohorts were separated by fertilization as either a 2 pronuclear zygote (2PN) or micro 3 pronuclear zygote (micro 3PN). PGT-A was performed to identify embryonic ploidy rates in embryos created from micro 3PN zygotes. The clinical outcomes of all transferred euploid micro 3PN zygotes were evaluated from frozen embryo transfer (FET) cycles.

RESULTS

During the designated study period, 75,903 mature oocytes were retrieved and underwent ICSI. Of these, 60,161 were fertilized as 2PN zygotes (79.3%) and 183 fertilized as micro 3PN zygotes (0.24%). Of the micro 3PN-derived embryos that underwent biopsy, 27.5% (n=11/42) were deemed euploid by PGT-A, compared to 51.4% (n=12,301/23,923) of 2PN-derived embryos, p=0.06. Four micro 3PN-derived embryos were transferred in subsequent single euploid FET cycles, which includes one live birth and one ongoing pregnancy.

CONCLUSION

Micro 3PN zygotes that develop to the blastocyst stage and meet the criteria for embryo biopsy have the potential to be euploid by preimplantation genetic testing for aneuploidy (PGT-A) and if selected for transfer can achieve a live birth. Although there are a significantly lower number of micro 3PN embryos that make it to blastocyst biopsy, the potential to continue to culture abnormally fertilized oocytes may give these patients a chance at pregnancy that they previously did not have.

A program of successive gene expression in mouse one-cell embryos

At the moment of union in fertilization, sperm and oocyte are transcriptionally silent. The ensuing onset of embryonic transcription (embryonic genome activation [EGA]) is critical for development, yet its timing and profile remain elusive in any vertebrate species. We here dissect transcription during EGA by high-resolution single-cell RNA sequencing of precisely synchronized mouse one-cell embryos. This reveals a program of embryonic gene expression (immediate EGA [iEGA]) initiating within 4 h of fertilization. Expression during iEGA produces canonically spliced transcripts, occurs substantially from the maternal genome, and is mostly downregulated at the two-cell stage. Transcribed genes predict regulation by transcription factors (TFs) associated with cancer, including c-Myc. Blocking c-Myc or other predicted regulatory TF activities disrupts iEGA and induces acute developmental arrest. These findings illuminate intracellular mechanisms that regulate the onset of mammalian development and hold promise for the study of cancer.

Prediction of live birth in vitrified-warmed 1PN-derived blastocyst transfer: Overall quality grade, ICM, TE, and expansion degree

Background: Numerous studies have reported that transfer of blastocysts derived from monopronuclear (1PN) zygotes achieved live births. However, the potential value of morphology grading for the prediction of 1PN blastocyst viability is unclear, and the blastocyst selection criterion for successful pregnancy has not been set up yet. The aim of this study is to assess the ability of the blastocyst morphology grading system based on three parameters, namely, inner cell mass (ICM), trophectoderm (TE), and expansion degree and to predict outcomes of a cycle with single 1PN blastocyst transfer.

Methods: A total of 266 vitrified-warmed 1PN-derived blastocyst transfer cycles for IVF treatment at Shanghai Ninth People’s Hospital between 2007 and 2020 were included. The study was performed on single blastocyst transfers. Electronic records of patients were retrospectively analyzed. In the current study, the blastocysts were classified into three groups: “good,” 3-6AA, 3-6AB, 3-6BA; “medium,” 3-6BB, 3-6AC, 3-6CA; and “poor,” 3-6BC, 3-6CB, 3-6CC. The basal characteristics, embryo grading, and clinical outcomes were compared between the three groups. The association of morphology parameters with pregnancies and live births was analyzed. Logistic regression was adopted to set up a prediction model of live births.

Results: Transfer of the good-quality blastocysts achieved significant higher pregnancies (biochemical pregnancy: 59%; clinical pregnancy: 56.4%, and live birth 48.7%) than those in the group of the medium (biochemical pregnancy: 59%; clinical pregnancy: 49.6%; live birth: 40.4%) or poor-quality (biochemical pregnancy: 38.4%; clinical pregnancy: 34.9%; live birth: 26.7%) blastocysts (p &lt; 0.05). There was a significant association between ICM and live birth. A prediction model of live births involving ICM, TE, and expansion degree was set up.

Conclusion: In 1PN transfer cycles, a higher overall blastocyst quality is shown to correlate most strongly with optimal pregnancy and live birth outcomes. The selection of high-quality blastocysts for transfer should consider the ICM score first. The prediction model of live births based on ICM, TE, and expansion degree may help predict successful pregnancy in 1PN single-blastocyst transfer cycles.

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

Purpose

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

Method(s)

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

Result(s)

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

Conclusion

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

Developmental trajectory of monopronucleated zygotes after in vitro fertilization when they include both male and female genomes

OBJECTIVE

To examine the cause of monopronucleated zygote (1PN) formation that includes both maternal and paternal genomes.

DESIGN

Retrospective cohort study.

SETTING

Private fertility clinic.

PATIENT(S)

A total of 44 1PN and 726 2-pronuclear zygotes from 702 patients were observed using 2 different time-lapse observation systems.

INTERVENTION(S)

Previously recorded time lapse data were reviewed to examine the mechanism of 1PN formation.

MAIN OUTCOME MEASURE(S)

The distance between the position of the second polar body extrusion and the fertilization cone or epicenter/starting position of the cytoplasmic wave was measured, and the consequent data were analyzed. Cytoplasmic waves were confirmed using vector analysis software.

RESULT(S)

The cut-off value for the difference in the distance between the position of the second polar body extrusion and the fertilization cone or the epicenter/starting position of the cytoplasmic wave was 17 μm (AUC: 0.987, 95% CI: 0.976-0.999) for the Embryo Scope and 18 μm (AUC: 0.972, 95% CI: 0.955-0.988) for the iBIS time-lapse observation systems.

CONCLUSION(S)

In this study, it was found with a high degree of accuracy that a monopronucleus is formed when the fusion of the sperm takes place within 18 μm from the point of the second polar body extrusion. The theoretical chance of 1PN occurrence after in vitro fertilization is 2.7% when the sperm is considered to be fused anywhere in the plasma membrane of an oocyte.

Exploration of the Cytoplasmic Function of Abnormally Fertilized Embryos via Novel Pronuclear-Stage Cytoplasmic Transfer

In regular IVF, a portion of oocytes exhibit abnormal numbers of pronuclei (PN) that is considered as abnormal fertilization, and they are routinely discarded. However, it is known that abnormal ploidy still does not completely abandon embryo development and implantation. To explore the potential of cytoplasm from those abnormally fertilized oocytes, we developed a novel technique for the transfer of large cytoplasm between pronuclear-stage mouse embryos, and assessed its impact. A large volume of cytoplast could be efficiently transferred in the PN stage using a novel two-step method of pronuclear-stage cytoplasmic transfer (PNCT). PNCT revealed the difference in the cytoplasmic function among abnormally fertilized embryos where the cytoplasm of 3PN was developmentally more competent than 1PN, and the supplementing of fresh 3PN cytoplasm restored the impaired developmental potential of postovulatory “aged” oocytes. PNCT-derived embryos harbored significantly higher mitochondrial DNA copies, ATP content, oxygen consumption rate, and total cells. The difference in cytoplasmic function between 3PN and 1PN mouse oocytes probably attributed to the proper activation via sperm and may impact subsequent epigenetic events. These results imply that PNCT may serve as a potential alternative treatment to whole egg donation for patients with age-related recurrent IVF failure.

Monopronucleated (1PN) and tripronuclear (3PN) zygotes formation during assisted reproduction in POSEIDON group 4 patients: Emphasizing on polar bodies

AIM

Abnormal fertilization (1PN/3PN) and its accompanying polar body (PB) conditions have been less discussed in poor ovarian responders. By observing the PBs, we analyzed the mechanisms of abnormal fertilization and aimed to explore the role of intracytoplasmic sperm injection/in vitro fertilization (ICSI/IVF) in POSEIDON group 4 patients.

METHODS

An observational study. All fresh IVF/ICSI cycles from January 2018 to December 2019 were evaluated. The inclusion criteria were POSEIDON group 4. Fertilization and PB conditions were assessed 16-18 h post-insemination. Primary observation endpoints including normal fertilization, abnormal fertilization, and total fertilization failure rate.

RESULTS

A total of 351 cycles involving 180 patients met the inclusion criteria. Of these, 15 cycles reported no retrieved oocytes. Finally, 336 cycles (IVF, n = 267; ICSI, n = 69) were included. A total of 1005 oocytes and 939 embryos were assessed. The mean female age was 40.8 years, and the mean AMH level was 0.6 ng/mL. The normal fertilization rate was 69.7%. The zygote distribution was 18.7% 0PN, 3.9% 1PN, 66.9% 2PN, 9.5% 3PN, and 1.0% ≥4PN. For 1PN zygotes, 59% were denoted as 1PN2PB. The mean 3PN rate was 8.9%.

CONCLUSIONS

In POSEIDON group 4, most of the monopronucleated zygotes were 1PN2PB. Digyny (3PN1PB), due to failure to extrude the second PB, was the major cause of triploidy in which ICSI could not circumvent. The distribution of abnormally fertilized zygotes was similar in IVF and ICSI. To investigate the mechanisms of abnormal fertilization and assess whether ICSI is necessary, analysis of PB will provide important clues.

Plasticity of the human preimplantation embryo: developmental dogmas, variations on themes and self-correction

BACKGROUND

IVF for the treatment of infertility offers unique opportunities to observe human preimplantation development. Progress in time-lapse technology (TLT) and preimplantation genetic testing (PGT) has greatly expanded our knowledge of developmental patterns leading to a healthy pregnancy or developmental failure. These technologies have also revealed unsuspected plastic properties of the preimplantation embryo, at macromolecular, cellular and multicellular levels.

OBJECTIVE AND RATIONALE

This review focuses on the emerging concept of plasticity of the human embryo as revealed by recent evidence derived from TLT and PGT, calling for an updated and more precise redefinition of the boundaries between normal and abnormal development.

SEARCH METHODS

PubMed was used to search the MEDLINE database for peer-reviewed English-language original articles and reviews concerning human preimplantation development. Cross-searches were performed by adopting 'fertilisation', 'pronucleus', 'cleavage', 'multinucleation', 'compaction', 'embryo', 'preimplantation genetic testing', 'aneuploidy', mosaicism', 'micromanipulation', 'time-lapse microscopy' and 'IVF/assisted reproduction' as main terms. The most relevant publications, i.e. those concerning major phenomena occurring during normal and abnormal development-with a focus on the human species-were assessed and discussed critically.

OUTCOMES

Advances in TLT and PGT have revealed an astonishing plasticity and self-correction ability of the human preimplantation embryo in vitro. At fertilisation, an abnormal number of pronuclei do not always result in the formation of an aneuploid blastocyst. Animal studies and preliminary human observations indicate that combining of parental genomes may occur at the early cleavage stage, if not at fertilisation. Multinucleation occurs with much higher prevalence than previously thought and may be corrected at later cleavage stages. Irregular cleavage (multichotomous, direct, rapid and reverse cleavages) can generate chromosome segregation abnormalities that often lead to developmental arrest, but that sporadically may be confined to cells excluded from the blastocyst, and may sometimes result in viable pregnancy. Mitotic errors can generate mosaic blastocysts, but alternatively normal embryos may form from selective death or clonal depletion of aneuploid cells.

WIDER IMPLICATIONS

Deviations from developmental dogmas and the increasing evidence of plasticity of the human embryo challenge current embryological notions and suggest the need to write new rules governing cell cycle, cell determination and chromosome segregation during preimplantation development.

Comparison of the rates for reaching the blastocyst stage between normal and abnormal pronucleus embryos monitored by a time-lapse system in IVF patients

Objective

To compare the rates of blastocyst stage development between embryos fertilized after one (MPN) or more than two pronucleus (PN) (3PN, 4PN-multiPN) with those after 2PN in the same patients.

Material and Methods

The embryos of patients who had both abnormal PN (MPN, 3PN or 4PN) and normal fertilized (2PN) embryos after intracytoplasmic sperm injection (ICSI) fertilization, were followed with a time-lapse system following the ICSI procedure. The rates of reaching the blastocyst stage were compared between normal and abnormally fertilized embryos.

Results

One thousand eight hundred and twenty oocytes were collected from 140 patients and 1280 (70.3%) of them were fertilized. MPN, 2PN and 3PN, 4PN (multiPN) ratios of the embryos in the pronuclear stage were 11.4%, 83.13% and 5.47%, respectively. The rates of reaching the blastocyst stage among these embryos were 17.1%, 60.8% and 42.8% for MPN, 2PN and multiPN, respectively. The proportion reaching blastocyst development was significantly higher following 2PN compared to those after MPN and multiPN (p<0.05). Embryos developing after multiPN had significantly higher rates of reaching the blastocyst stage compared to those after MPN (p<0.01).

Conclusion

The majority of abnormally pronucleated embryos arrest without reaching the blastocyst stage. MultiPN embryos have a higher rate of blastocyst development than MPN embryos.

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.

Morphokinetic analysis of pronuclei using time-lapse cinematography in bovine zygotes

The morphokinetics of pronuclei (PN) are considered crucial factors affecting embryogenesis in mammals. Whereas, since bovine zygotes contain a large number of cytosolic lipid droplets, detailed observation of PN has not been performed. In this study, we visualized PN using time-lapse cinematography (TLC) with light microscopy for the first time in delipidated bovine zygotes. The proportions of 0 PN, 1PN, 2PN, and multi-PN in delipidated bovine zygotes were 10.1%, 6.5%, 72.7%, and 10.8%, respectively. Abnormal fertilization, including 1 PN and multi-PN, was observed in 15.6% of blastocysts. The times from IVF to PN appearance, PN fading, and first cleavage in 2 PN bovine zygotes that developed into blastocysts were 10.4, 25.5, and 27.6 h, respectively, which were similar to PN morphokinetics in humans. The 2 PN zygotes showed that the prolonged time from IVF to the appearance of PN and from the fading of PN to the first cleavage negatively affected blastocyst formation. The time from appearance to fading of PN in multi-PN zygotes that developed into blastocysts was longer than that in multi-PN zygotes that did not develop into blastocysts. Besides, among zygotes that developed into blastocysts, the time from appearance to fading of PN in multi-PN zygotes was longer than that in 2 PN and 1 PN zygotes. These results suggest that PN morphokinetic abnormalities are associated with subsequent embryonic development. Observation of PN in bovine zygotes by using non-invasive visible light TLC by delipidation could be a powerful tool to clarify the relationship between PN morphokinetics and developmental competence.

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.

Molar pregnancy after in vitro fertilization with euploid single embryo transfer

Objective

To describe a case of molar pregnancy after in vitro fertilization (IVF) resulting from the transfer of a euploid embryo derived from a monopronuclear zygote.

Design

Case report and review of the literature.

Setting

Private practice IVF center.

Patients

A 42-year-old woman, gravida 3 para 0, with advanced maternal age and infertility who underwent IVF.

Interventions

Preimplantation genetic testing for aneuploidy using next-generation sequencing, single frozen euploid blastocyst transfer, and medical management of suspected missed abortion.

Main Outcome Measures

Genetic examination of products of conception and correlation with embryonic preimplantation genetic testing for aneuploidy results.

Results

Transfer of the euploid embryo derived from an abnormally fertilized oocyte (monopronuclear zygote) resulted in a clinical pregnancy suspected to be a missed abortion. Products of conception collected after medical management of the suspected missed abortion were analyzed using next-generation sequencing with the report "46,XX complete molar pregnancy".

Conclusions

To our knowledge, this is the first account of a complete molar pregnancy resulting from the transfer of a reported euploid embryo, highlighting the importance of understanding the limitations of genetic testing platforms in the setting of abnormally fertilized oocyte-derived embryos.

Genetic ethics and mtDNA replacement techniques

The United Kingdom parliament made history in 2015 when they voted to allow the use of mitochondrial (mtDNA) replacement techniques. Mitochondrial diseases are genetically inherited and currently, the only known cure is replacement therapies. However, most other countries have been slow to adopt policy changes that allow for mtDNA replacement due to the ethical challenges of the techniques. While there are ethical challenges concerning mtDNA replacement, there is a need to address these challenges and allow these techniques in the US to provide treatment for individuals affected. This paper first addresses mitochondrial diseases and replacement techniques currently used and analyzes ethical challenges related to the interventions, such as safety, efficacy, and contributed genetic material from three individuals. This paper then addresses how the ethical principles, beneficence, nonmaleficence, autonomy and justice support mtDNA replacement. Suggestions on how the US can allow mtDNA replacement by adopting similar policy changes to the UK are provided, as well as additional measures to protect patients. Given the rate of individuals affected, severity of mitochondrial diseases, and lack of treatment options available, it's important to address how to overcome ethical challenges and policy barriers.

The Incidence of Mosaicism for Individual Chromosome in Human Blastocysts Is Correlated With Chromosome Length

Mosaicism, known as partial aneuploidies, mostly originates from mitotic errors during the post-zygotic stage; it consists of different cell lineages within a human embryo. The incidence of mosaicism has not been shown to correlate with maternal age, and its correlation with individual chromosome characteristics has not been well investigated. In this study, the results of preimplantation genetic testing for aneuploidy (PGT-A) derived from 4,036 blastocysts (930 IVF couples) were collected from 2015 to 2017. Via next-generation sequencing for comprehensive chromosome screening, embryo ploidy was identified as aneuploid, mosaic, and euploid. Total mosaicism was classified into two categories: "mosaic euploid/aneuploidy" (with mosaic aneuploidy between 20 and 80%) and "mosaic and aneuploidy" (a uniformly abnormal embryo superimposed with mosaic aneuploidies). Frequency of mosaicism was analyzed according to the function of chromosomal lengths, which divides involved chromosomes into three groups: group A (156-249 Mb), group B (102-145 Mb), and group C (51-90 Mb). The results show that the aneuploidy was more frequent in group C than in group A and group B (A: 23.7%, B: 35.1, 41.2%, p < 0.0001), while the mosaicism was more frequent in group A and group B than in group C [(Mosaic euploid/aneuploid) A: 14.6%, B: 12.4%, C: 9.9%, p < 0.0001; (mosaic and aneuploid) A: 21.3%, B: 22.9%, C: 18.9%, p < 0.0001; (Total mosaicism) A: 35.9%, B: 35.3%, C: 28.8%, p < 0.0001]. The significantly higher frequency of aneuploidy was on the shorter chromosome (< 90 Mb), and that of mosaicism was on the longer chromosomes (> 100 Mb). The length association did not reach significance in the patients with advanced age (≥ 36 years), and of the chromosome-specific mosaicism rate, the highest prevalence was on chromosome 14 (5.8%), 1 (5.7%), and 9 (5.6%). Although the length association was observed via group comparison, there may be affecting mechanisms other than chromosomes length. Eventually, twenty patients with mosaic embryo cryotransfers resulted in six live births. No significant correlation was observed between the transfer outcomes and chromosome length; however, the analysis was limited by small sample size.

Developmental Potential of Abnormally Fertilized Oocytes and the Associated Clinical Outcomes

This study aims to investigate the embryo development potential of extending the culture of abnormally fertilized zygotes with no pronuclear (0PN), monopronuclear (1PN), and poor-quality day 3 embryos and to determine the associated clinical outcomes. This is a retrospective study performed between January 2014 and May 2018 at Jinhua People's Hospital. The normal developed embryos and the abnormal 0PN, 1PN, and poor-quality day 3 embryos were cultured to day 5 or 6 for embryo transfer. Clinical outcomes resulting from abnormal embryos and normally developed embryos were compared. A total of 6466 embryos (1542 0PN, 852 1PN, and 4072 poor-quality day 3 embryos) from 831 treatment cycles were cultured to the blastocyst stage. The total blastulation rate was 17.3% (1121/6466) with 18.2% in 0PN, 26.1% in 1PN, and 15.2% in poor-quality day 3 embryos. The rate for good-quality blastocyst formation was 9.5% (616/6466) with 11.2% in 0PN group, 14.8% in 1PN group, and 7.8% in poor-quality day 3 embryos, respectively. Blastulation rates of 0PN and 1PN derived from intracytoplasmic sperm injection (ICSI) were significantly lower compared with the in vitro fertilization group. A total of 243 cycles were transferred with blastocysts originating from abnormal embryos, resulting in 109 (44.9%) clinical pregnancies and 19 (17.4%) miscarriages; in the control group, a total of 350 cycles resulted in 214 (61.1%) clinical pregnancies and 18 (8.4%) miscarriages. The live birth rate was significantly lower in the abnormal embryo group than that in the control group. Collectively, conventional in vitro fertilization derived 0PN and 1PN zygotes, not ICSI, together with day 3 embryos with poor quality, that were able to reach the blastocyst stage and produce a fair pregnancy rate and live birth rate.

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

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

Initial ovarian sensitivity index predicts embryo quality and pregnancy potential in the first days of controlled ovarian stimulation

BACKGROUND

To determine if a modified ovarian sensitivity index (MOSI), based on initial follicular measurements and the initial follicle-stimulating hormone (FSH) dose, can predict the production of high-quality embryos for successful implantation during in vitro fertilization (IVF).

METHODS

This study consisted of two phases: 1) a retrospective study and 2) a prospective observational study. For the first phase, 363 patients charts were reviewed, of which 283 had embryos transferred. All women underwent a standardized antagonist-based IVF protocol. At the first follow-up (Day 3/4), the number and size of the follicles were determined. MOSI was calculated as ln (number follicles (≥6 mm) × 1000 / FSH initial dose). Afterward, the number and quality of the ova, embryo development, and the number and quality of the blastocysts were determined. Embryo implantation was confirmed by β-hCG. For the second phase, 337 IVF cycles were followed to determine MOSI's accuracy.

RESULTS

MOSI could predict the production of ≥4 high-quality embryos by Day 2 (AUC = 0.69, 95%CI:0.63-0.75), ≥2 blastocysts (AUC = 0.74, 95%CI:0.68-0.79), and ≥ 35% rate of blastocyst formation (AUC = 0.65, 95%CI:0.58-0.72). Using linear regression, MOSI was highly associated with the number of ova captured (β = 5.15), MII oocytes (β = 4.31), embryos produced (β = 2.90), high-quality embryos (β = 0.98), and the blastocyst formation rate (β = 0.06, p < 0.01). Using logistic regression, MOSI was highly associated with achieving ≥4 high-quality embryos (odds ratio = 2.80, 95%CI:1.90-4.13), ≥2 blastocysts (odds ratio = 3.40, 95%CI:2.33-4.95), and ≥ 35% blastocysts formation rate (odds ratio = 1.96, 95%CI:1.31-2.92). This effect was independent of age, BMI, and antral follicle count. For implantation, MOSI was significantly associated with successful implantation (odds ratio = 1.79, 95%CI:1.25-2.57). For the prospective study, MOSI was highly accurate at predicting ≥6 high-quality embryos on Day 2 (accuracy = 68.5%), ≥6 blastocysts (accuracy = 68.0%), and a blastocyst formation rate of ≥35% (accuracy = 61.4%).

CONCLUSION

MOSI was highly correlated with key IVF parameters that are associated with achieved pregnancy. Using this index with antagonist cycles, clinicians may opt to stop an IVF cycle, under the assumption that the cycle will fail to produce good blastocysts, preventing wasting the patient's resources and time.

Blastocysts Derived From 0PN Oocytes: Genetic And Clinical Results

Objective

To analyze the genetic and clinical outcomes of blastocysts derived from 0PN oocytes after IVF/ICSI.

Methods

This retrospective observational study included patients aged 40 years or younger submitted to IVF/ICSI with their own oocytes and with blastocysts derived from 0PN oocytes between January 2015 and April 2018. The clinical outcomes of 0PN blastocyst transfers were analyzed. Genetic tests were performed on biopsied 0PN blastocysts with Next Generation Sequencing.

Results

A total of 27 0PN blastocysts were transferred, yielding an implantation rate of 48.0% and an ongoing pregnancy rate of 50.0%. The transfers resulted in 13 live births (59.0% live birth rate). Genetic test results revealed that four of the 17 0PN blastocysts biopsied were 46XX; three were 46XY; and 10 were aneuploid embryos, awarding a diploid rate to 76.4% (13/17).

Conclusion

Almost half of the 0PN blastocysts implanted (48.0%) and 13 healthy babies were born. More than three quarters (76.4%) of the 0PN blastocysts were diploid, thus ruling out the possibility of parthenogenetic activation. Our study indicated that the transfer of 0PN blastocysts is a safe, worthy option when the number of normal 2PN embryos is insufficient.

Value of transferring embryos derived from monopronucleated (1PN) zygotes at the time of fertilization assessment

This paper is a retrospective analysis of the sole transfer of monopronucleated zygotes (1PN) embryos both in in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) to determine the value of transferring embryos formed from 1PN. In fresh cycles, 1PN cleavage-stage embryos (1PN cleavage fresh) were transferred. In frozen–thawed cycles, 1PN blastocyst-stage embryos (1PN blast frozen) were transferred. We used comparison groups: for fresh cycles, 2PN cleavage-stage embryos (2PN cleavage fresh) were transferred; and for frozen–thawed cycles, 2PN blastocyst-stage embryos (2PN blast frozen) were transferred. Comparison groups were matched for cycle and patient characteristics to the 1PN group. Finally, for fresh cycles, live birth rates (LBR) in the 1PN cleavage group were significantly lower than those in 2PN cleavage group, both for IVF [LBR = 7.64% vs. pregnancy rate (PR) = 22.12%, P = 0.003, respectively] and ICSI (LBR = 0% vs. LBR = 20.00%, P < 0.001, respectively). For frozen–thawed IVF cycles, the PR in the 1PN blastocyst group were comparable with those of the 2PN blastocyst group (1PN: LBR = 33.14% vs. 2PN: LBR = 37.24%, P = 0.289, respectively), while in ICSI, the PR in the 1PN blastocyst group were lower than those in the 2PN blastocyst group (LBR = 15.25% vs. LBR = 40.68%, P = 0.002, respectively). So, for IVF, blastocyst culture was capable of selecting normal 1PN embryos for transfer and achieves satisfying outcomes. However, for ICSI, blastocyst culture was not effective enough to eliminate abnormal embryos and 1PN embryo transfer needed to be treated with caution.

Morphokinetics and in vitro developmental potential of monopronucleated ICSI zygotes until the blastocyst stage

The aim of this study was to provide a more comprehensive understanding of 1PN intracytoplasmic sperm injection (ICSI) zygotes. To achieve this objective, we assessed whether all 1PN-derived embryos showed a similar morphokinetic pattern, and if the morphokinetic behaviour of 1PN-derived embryos was comparable with that of 2PN-derived embryos. In total, 149 1PN ICSI zygotes (study group) and 195 2PN ICSI zygotes (control group) were included in the study. Embryo development potential was evaluated in terms of blastocyst rate. Morphokinetic parameters, including the pronucleus diameter and kinetics of in vitro development, were also analyzed. Embryos derived from 1PN ICSI zygotes showed impaired development compared with 2PN-derived embryos, with blastocyst rates of 28.9% and 67.2%, respectively. The diameter of the pronucleus of 1PN zygotes was larger than that of 2PN zygotes. When compared with 2PN-derived embryos, those derived from 1PN zygotes had a visible pronucleus for a shorter time, in addition to a longer syngamy time and slower kinetic behaviour from two to nine cells. When 1PN-derived blastocysts and 2PN-derived blastocysts were compared, the developmental kinetics were similar in both groups, except for a delayed and longer duration of the compaction phase in 1PN-derived embryos. In conclusion, monopronucleated ICSI zygotes present differences in developmental capacity and morphokinetic behaviour compared with 2PN ICSI zygotes, showing particular morphokinetic parameters related to pronucleus formation. Only the 1PN ICSI-derived embryos that reached the blastocyst stage have similar morphokinetic development to blastocysts from 2PN zygotes.

Chromosomal mosaicism in human blastocysts: the ultimate diagnostic dilemma

BACKGROUND

Trophectoderm (TE) biopsy and next generation sequencing (NGS) are currently the preferred techniques for preimplantation genetic testing for aneuploidies (PGT-A). Although this approach delivered important improvements over previous testing strategies, increased sensitivity has also prompted a rise in diagnoses of uncertain clinical significance. This includes reports of chromosomal mosaicism, suggesting the presence of karyotypically distinct cells within a single TE biopsy. Given that PGT-A relies on the chromosomal constitution of the biopsied cells being representative of the entire embryo, the prevalence and clinical implications of blastocyst mosaicism continue to generate considerable controversy.

OBJECTIVE AND RATIONALE

The objective of this review was to evaluate existing scientific evidence regarding the prevalence and impact of chromosomal mosaicism in human blastocysts. We discuss insights from a biological, technical and clinical perspective to examine the implications of this diagnostic dilemma for PGT-A.

SEARCH METHODS

The PubMed and Google Scholar databases were used to search peer-reviewed publications using the following terms: ‘chromosomal mosaicism’, ‘human’, ‘embryo’, ‘blastocyst’, ‘implantation’, ‘next generation sequencing’ and ‘clinical management’ in combination with other keywords related to the subject area. Relevant articles in the English language, published until October 2019 were critically discussed.

OUTCOMES

Chromosomal mosaicism predominately results from errors in mitosis following fertilization. Although it appears to be less pervasive at later developmental stages, establishing the true prevalence of mosaicism in human blastocysts remains exceedingly challenging. In a clinical context, blastocyst mosaicism can only be reported based on a single TE biopsy and has been ascribed to 2–13% of embryos tested using NGS. Conversely, data from NGS studies disaggregating whole embryos suggests that mosaicism may be present in up to ~50% of blastocysts. However, differences in testing and reporting strategies, analysis platforms and the number of cells sampled inherently overshadow current data, while added uncertainties emanate from technical artefacts. Moreover, laboratory factors and aspects of in vitro culture generate further variability. Outcome data following the transfer of blastocysts diagnosed as mosaic remain limited. Current studies suggest that the transfer of putative mosaic embryos may lead to healthy live births, but also results in significantly reduced ongoing pregnancy rates compared to the transfer of euploid blastocysts. Observations that a subset of mosaic blastocysts has the capacity to develop normally have sparked discussions regarding the ability of embryos to self-correct. However, there is currently no direct evidence to support this assumption. Nevertheless, the exclusion of mosaic blastocysts results in fewer embryos available for transfer, which may inevitably compromise treatment outcomes.

WIDER IMPLICATIONS

Chromosomal mosaicism in human blastocysts remains a perpetual diagnostic and clinical dilemma in the context of PGT-A. This review offers an important scientific resource, informing about the challenges, risks and value of diagnosing mosaicism. Elucidating these uncertainties will ultimately pave the way towards improved clinical and patient management.

Genome-wide haplotyping embryos developing from 0PN and 1PN zygotes increases transferrable embryos in PGT-M

STUDY QUESTION

Can genome-wide haplotyping increase success following preimplantation genetic testing for a monogenic disorder (PGT-M) by including zygotes with absence of pronuclei (0PN) or the presence of only one pronucleus (1PN)?

SUMMARY ANSWER

Genome-wide haplotyping 0PNs and 1PNs increases the number of PGT-M cycles reaching embryo transfer (ET) by 81% and the live-birth rate by 75%.

WHAT IS KNOWN ALREADY

Although a significant subset of 0PN and 1PN zygotes can develop into balanced, diploid and developmentally competent embryos, they are usually discarded because parental diploidy detection is not part of the routine work-up of PGT-M.

STUDY DESIGN, SIZE, DURATION

This prospective cohort study evaluated the pronuclear number in 2229 zygotes from 2337 injected metaphase II (MII) oocytes in 268 cycles. PGT-M for 0PN and 1PN embryos developing into Day 5/6 blastocysts with adequate quality for vitrification was performed in 42 of the 268 cycles (15.7%). In these 42 cycles, we genome-wide haplotyped 216 good quality embryos corresponding to 49 0PNs, 15 1PNs and 152 2PNs. The reported outcomes include parental contribution to embryonic ploidy, embryonic aneuploidy, genetic diagnosis for the monogenic disorder, cycles reaching ETs, pregnancy and live birth rates (LBR) for unaffected offspring.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Blastomere DNA was whole-genome amplified and hybridized on the Illumina Human CytoSNP12V2.1.1 BeadChip arrays. Subsequently, genome-wide haplotyping and copy-number profiling was applied to investigate the embryonic genome architecture. Bi-parental, unaffected embryos were transferred regardless of their initial zygotic PN score.

MAIN RESULTS AND THE ROLE OF CHANCE

A staggering 75.51% of 0PN and 42.86% of 1PN blastocysts are diploid bi-parental allowing accurate genetic diagnosis for the monogenic disorder. In total, 31% (13/42) of the PGT-M cycles reached ET or could repeat ET with an unaffected 0PN or 1PN embryo. The LBR per initiated cycle increased from 9.52 to 16.67%.

LIMITATIONS, REASONS FOR CAUTION

The clinical efficacy of the routine inclusion of 0PN and 1PN zygotes in PGT-M cycles should be confirmed in larger cohorts from multicenter studies.

WIDER IMPLICATIONS OF THE FINDINGS

Genome-wide haplotyping allows the inclusion of 0PN and 1PN embryos and subsequently increases the cycles reaching ET following PGT-M and potentially PGT for aneuploidy (PGT-A) and chromosomal structural rearrangements (PGT-SR). Establishing measures of clinical efficacy could lead to an update of the ESHRE guidelines which advise against the use of these zygotes.

STUDY FUNDING/COMPETING INTEREST(S)

SymBioSys (PFV/10/016 and C1/018 to J.R.V. and T.V.), the Horizon 2020 WIDENLIFE: 692065 to J.R.V., T.V., E.D., A.D. and M.Z.E. M.Z.E., T.V. and J.R.V. co-invented haplarithmisis (‘Haplotyping and copy-number typing using polymorphic variant allelic frequencies’), which has been licensed to Agilent Technologies. H.M. is fully supported by the (FWO) (ZKD1543-ASP/16). The authors have no competing interests to declare.

The influence of clinical and laboratory factors on the formation of monopronucleated zygotes after intracytoplasmic sperm injection (ICSI)

The aim of the present study was to determine whether clinical or laboratory factors can influence the development of single pronucleated zygotes (1PN) and two polar bodies (PB) after ICSI. In total, 341 ICSI cycles performed at FertiClinic-Villa Margherita from January 2012 to December 2014 were enrolled in the study. Group A included 240 cycles with no 1PN−2PB while group B included 101 cycles with one or more 1PN−2PB. Age, stimulation protocol, infertility factor, amount of gonadotropin administered, duration of therapy, peak estradiol levels, number of follicles at maturation triggering, oocytes retrieved and mature oocytes, time between retrieval and injection and sperm characteristics were compared between groups. In opposition to previous results showing no relationship between 1PN occurrence and clinical or laboratory variables, we observed that 1PN−2PB zygote formation seems to be associated with a lower female age, higher level of E2 and higher number of follicles on day of oocyte maturation triggering, higher number of astenozoospermic male patients, more oocytes retrieved at pick-up, more mature oocytes (MII) and longer time to injection.

Correlation between the pronucleus size and the potential for human single pronucleus zygotes to develop into blastocysts : 1PN zygotes with large pronuclei can expect an embryo development to the blastocyst stage that is similar to the development of 2PN zygotes

PURPOSE

In this study, we examined the correlation between pronucleus size and the potential for human single pronucleus (1PN) zygotes to develop into blastocysts after IVF and ICSI.

METHODS

This study included 112 patients who underwent a total of 112 cycles of IVF/ICSI. To evaluate embryo development, 1PN zygotes were compared with 2PN zygotes in the same IVF/ICSI cycle (control cycles) using time-lapse live embryo imaging. To assess the potential for blastocyst formation, cutoff values for pronuclear area and diameter were established through receiver operating characteristic curve analysis, after which 1PN zygotes were classified based on those cutoff values.

RESULTS

Among 1PN zygotes cultured to day 5/6, the rate of embryo development was significantly lower than from 2PN zygotes. However, the rates of blastocyst formation and good quality blastocysts from 1PN zygotes with large pronuclear areas (≥ 710 μm²) or diameters (≥ 31 μm) were significantly higher than from 1PN zygotes with smaller pronuclear areas (≤ 509, 510-609, and 610-709 μm²) or diameters (≤ 24, 25-27,and 28-30 μm) (P < 0.01). Moreover, the results for 1PN zygotes with large pronuclei were similar to those for 2PN zygotes.

CONCLUSIONS

The developmental potential of 1PN zygotes with large pronuclear areas (≥ 710 μm²) or diameters (31 μm) appears to be similar to that of 2PN zygotes, and measurement of pronuclear area or diameter in 1PN zygotes is a simple, potentially useful, clinical method.