Novel Time-Lapse Parameters Correlate with Embryo Ploidy and Suggest an Improvement in Non-Invasive Embryo Selection

Time-lapse analysis of embryos classified as euploid, mosaic, and aneuploid after embryonic trophectoderm biopsy

PURPOSE

Analyze morphokinetic, morphology, and KIDscore™Day5 in different PGT-A classes, focusing on putative mosaicism level and type.

METHODS

The single-center retrospective study analyzed 832 embryoscope-cultured blastocysts from cycles with at least one putative mosaic, conducted from 2020 to 2022. A P-value < 0.05 was considered statistically significant.

RESULTS

Putative mosaic embryos were significantly delayed compared to euploid in tPNF, t2, t4, t7, and t8 but significantly faster than aneuploid in tPNF, t2, t3, t4, t5, tSC, tM, tSB, and tB. Regarding the level, low-putative mosaic embryos (< 50%) showed significantly earlier tSC, tM, tSB, and tB compared to aneuploid, whereas high-putative mosaic embryos exhibited significantly earlier tSB and tB. Concerning the type of putative mosaicism, segmental aneuploidies reached significantly earlier t8, tM, and tB than complex aneuploidies. The study also investigated the usefulness of KIDscore™Day5 for embryo selection as an additional tool to PGT-A. A significant decrease in KIDscore™Day5 was observed from euploid to low-putative mosaic, from high-putative mosaic to aneuploid, and between segmental and complex-putative mosaic. The observed differences in KIDscore™Day5 were partially confirmed by transfer results: euploid blastocysts showed the most favorable clinical outcomes compared to low- and high-putative mosaics. Additionally, both euploid and segmental putative mosaic embryos exhibited the best clinical results compared to whole chromosome and complex putative mosaic. Moreover, within the same PGT-A class, embryos with the lowest KIDscore™Day5 values had significantly lower clinical results.

CONCLUSIONS

The data highlight that morphology, morphokinetics, and chromosome content in trophectoderm biopsy are closely related, and the KIDscore™Day5 algorithm reflects this interplay.

CRISPR/Cas9-editing of PRNP in Alpine goats

Misfolding of the cellular PrP (PrPc) protein causes prion disease, leading to neurodegenerative disorders in numerous mammalian species, including goats. A lack of PrPc induces complete resistance to prion disease. The aim of this work was to engineer Alpine goats carrying knockout (KO) alleles of PRNP, the PrPc-encoding gene, using CRISPR/Cas9-ribonucleoproteins and single-stranded donor oligonucleotides. The targeted region preceded the PRNPTer mutation previously described in Norwegian goats. Genome editors were injected under the zona pellucida prior to the electroporation of 565 Alpine goat embryos/oocytes. A total of 122 two-cell-stage embryos were transferred to 46 hormonally synchronized recipient goats. Six of the goats remained pregnant and naturally gave birth to 10 offspring. Among the 10 newborns, eight founder animals carrying PRNP genome-edited alleles were obtained. Eight different mutated alleles were observed, including five inducing KO mutations. Three founders carried only genome-edited alleles and were phenotypically indistinguishable from their wild-type counterparts. Among them, one male carrying a one base pair insertion leading to a KO allele is currently used to rapidly extend a PRNP-KO line of Alpine goats for future characterization. In addition to KO alleles, a PRNPdel6 genetic variant has been identified in one-third of founder animals. This new variant will be tested for its potential properties with respect to prion disease. Future studies will also evaluate the effects of genetic background on other characters associated with PRNP KO, as previously described in the Norwegian breed or other species.

Preimplantation development analysis of aneuploid embryos with different chromosomal abnormalities

Background

The change of morphokinetic pattern in aneuploid embryos will facilitate the non-invasive selection of euploid embryos. In this study, we investigated the impact of different chromosomal abnormalities on the morphokinetic patterns of embryonic development.

Methods

Our cohort includes 939 time-lapse preimplantation genetic testing cycles performed between January 2019 and July 2022 at a single academic fertility center, with a total of 2876 biopsied blastocysts. Intracytoplasmic sperm injection, blastocyst culture, trophectoderm biopsy, time-lapse monitoring, and next-generation sequencing were performed.

Results

After adjusting for patient- and cycle-related factors, six morphokinetic parameters (t5, P = 0.006; t8, P = 0.048; tSB, P < 0.001; tB,P < 0.001; t5-t2, P = 0.004; tB-tSB, P < 0.001) were significant in multilevel mixed-effects logistic regression model analysis for morphokinetic parameters to predict euploid or aneuploid embryos. None of the patient- or cycle-related factors systematically affected any morphokinetic parameter. Morphokinetic parameters of late cleavage and blastocyst stages in embryos with chromosome fragment deletion (t4 to t8, tB, t5-t2, tB-tSB, ECC2, ECC3, s2, P < 0.05) or duplication (t4, t5, tSB, tB, t5-t2, P < 0.05) were prolonged, and the morphokinetic parameters of the blastocyst stage in monosomic embryos (tSB, tB, tB-tSB, P < 0.01) were prolonged. Partial or complete chromosome 20 or 22 deletion can cause significant delays in multiple parameters of cleavage and blastocyst stages (from t4 to tB, P < 0.05).

Conclusions

Our study found that different chromosomal abnormalities have different effects on the morphokinetic parameters. Significant delays in morphokinetic parameters at different stages were found in fragment-mutated embryos and monosomic embryos. This can provide insights into the pre-implantation development pattern of aneuploid embryos and help non-invasive embryo selection.

Making and Selecting the Best Embryo in In vitro Fertilization

Currently, most assisted reproduction units transfer a single embryo to avoid multiple pregnancies. Embryologists must select the embryo to be transferred from a cohort produced by a couple during a cycle. This selection process should be accurate, non-invasive, inexpensive, reproducible, and available to in vitro fertilization (IVF) laboratories worldwide. Embryo selection has evolved from static and morphological criteria to the use of morphokinetic embryonic characteristics using time-lapse systems and artificial intelligence, as well as the genetic study of embryos, both invasive with preimplantation genetic testing for aneuploidies (PGT-A) and non-invasive (niPGT-A). However, despite these advances in embryo selection methods, the overall success rate of IVF techniques remains between 25 and 30%. This review summarizes the different methods and evolution of embryo selection, their strengths and limitations, as well as future technologies that can improve patient outcomes in the shortest possible time. These methodologies are based on procedures that are applied at different stages of embryo development, from the oocyte to the cleavage and blastocyst stages, and can be used in laboratory routine.

Correlation between Human Embryo Morphokinetics Observed through Time-Lapse Incubator and Life Birth Rate

(1) Background: Does the variation in sequential development times of embryos, observed through time-lapse monitoring, between the two study groups play a role in predicting pregnancy success? (2) Methods: The prospective double-arm study was to identify the morphokinetic parameters specific to embryos that were capable of implanting and were conducted on 89 embryos cultured in the Esco Miri time-lapse incubator, divided into two groups: Lot A, consisting of 57 embryos that successfully implanted and resulted in life birth rate (LBR), and Lot B (NLB), comprising 32 embryos that did not implant, leading to a negative beta-hCG outcome. (3) Results: Baseline characteristics, including female age, were not found to be statistically significant (p > 0.01). In contrast, there is a highly statistically significant difference concerning oocytes (p = 0.0029). Morphokinetic variables represented by sequential culture times were not statistically significant (p > 0.01) when comparing the two groups. However, the negative mean differences between these parameters suggest that the times for Lot A are better (shorter) than those for Lot B. While not statistically significant, these differences may still have practical significance. In the case of grading, the difference is considered to be extremely statistically significant (p < 0.01). (4) Conclusions: Although there are no statistically significant differences in sequential timings (p > 0.01) between the two groups, there are parameters indicating predictive potential for exploring pregnancy in embryo morphokinetics.

The severity of meiotic aneuploidy is associated with altered morphokinetic variables of mouse oocyte maturation

STUDY QUESTION

Is there an association between morphokinetic variables of meiotic maturation and the severity of aneuploidy following in vitro maturation (IVM) in the mouse?

SUMMARY ANSWER

The severity of meiotic aneuploidy correlates with an extended time to first polar body extrusion (tPB1) and duration of meiosis I (dMI).

WHAT IS KNOWN ALREADY

Morphokinetic variables measured using time-lapse technology allow for the non-invasive evaluation of preimplantation embryo development within clinical assisted reproductive technology (ART). We recently applied this technology to monitor meiotic progression during IVM of mouse gametes. Whether there is a relationship between morphokinetic variables of meiotic progression and aneuploidy in the resulting egg has not been systematically examined at the resolution of specific chromosomes. Next-generation sequencing (NGS) is a robust clinical tool for determining aneuploidy status and has been reverse-translated in mouse blastocysts and oocytes. Therefore, we harnessed the technologies of time-lapse imaging and NGS to determine the relationship between the morphokinetics of meiotic progression and egg aneuploidy.

STUDY DESIGN SIZE DURATION

Cumulus-oocyte complexes were collected from large antral follicles from hyperstimulated CD-1 mice. Cumulus cells were removed, and spontaneous IVM was performed in the absence or presence of two doses of Nocodazole (25 or 50 nM) to induce a spectrum of spindle abnormalities and chromosome segregation errors during oocyte meiosis. Comprehensive chromosome screening was then performed in the resulting eggs, and morphokinetic variables and ploidy status were compared across experimental groups (control, n = 11; 25 nM Nocodazole, n = 13; 50 nM Nocodazole, n = 23).

PARTICIPANTS/MATERIALS SETTING METHODS

We monitored IVM in mouse oocytes using time-lapse microscopy for 16 h, and time to germinal vesicle breakdown (tGVBD), tPB1, and dMI were analyzed. Following IVM, comprehensive chromosome screening was performed on the eggs and their matched first polar bodies via adaptation of an NGS-based preimplantation genetic testing for aneuploidy (PGT-A) assay. Bioinformatics analysis was performed to align reads to the mouse genome and determine copy number-based predictions of aneuploidy. The concordance of each polar body-egg pair (reciprocal errors) was used to validate the results. Ploidy status was categorized as euploid, 1-3 chromosomal segregation errors, or ≥4 chromosomal segregation errors. Additionally, aneuploidy due to premature separation of sister chromatids (PSSC) versus non-disjunction (NDJ) was distinguished.

MAIN RESULTS AND THE ROLE OF CHANCE

We applied and validated state-of-the-art NGS technology to screen aneuploidy in individual mouse eggs and matched polar bodies at the chromosome-specific level. By performing IVM in the presence of different doses of Nocodazole, we induced a range of aneuploidy. No aneuploidy was observed in the absence of Nocodazole (0/11), whereas IVM in the presence of 25 and 50 nM Nocodazole resulted in an aneuploidy incidence of 7.69% (1/13) and 82.61% (19/23), respectively. Of the aneuploid eggs, 5% (1/20) was due to PSSC, 65% (13/20) to NDJ, and the remainder to a combination of both. There was no relationship between ploidy status and tGVBD, but tPB1 and the dMI were both significantly prolonged in eggs with reciprocal aneuploidy events compared to the euploid eggs, and this scaled with the severity of aneuploidy. Eggs with ≥4 aneuploid chromosomes had the longest tPB1 and dMI (P < 0.0001), whereas eggs with one to three aneuploid chromosomes exhibited intermediate lengths of time (P < 0.0001).

LARGE SCALE DATA

N/A.

LIMITATIONS REASONS FOR CAUTION

We used Nocodazole in this study to disrupt the meiotic spindle and induce aneuploidy in mouse oocytes. Whether the association between morphokinetic variables of meiotic progression and the severity of aneuploidy occurs with other compounds that induce chromosome segregation errors remain to be investigated. In addition, unlike mouse oocytes, human IVM requires the presence of cumulus cells, which precludes visualization of morphokinetic variables of meiotic progression. Thus, our study may have limited direct clinical translatability.

WIDER IMPLICATIONS OF THE FINDINGS

We validated NGS in mouse eggs to detect aneuploidy at a chromosome-specific resolution which greatly improves the utility of the mouse model. With a tractable and validated model system for characterizing meiotic aneuploidy, investigations into the molecular mechanisms and factors which may influence aneuploidy can be further elaborated. Time-lapse analyses of morphokinetic variables of meiotic progression may be a useful non-invasive predictor of aneuploidy severity.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by the Bill & Melinda Gates Foundation (INV-003385). Under the grant conditions of the Foundation, a Creative Commons Attribution 4.0 Generic License has already been assigned to the Author Accepted Manuscript version that might arise from this submission. The authors have no conflict of interest to disclose.

The Association between Embryo Development and Chromosomal Results from PGT-A in Women of Advanced Age: A Prospective Cohort Study

Embryo morphology and morphokinetics have been studied for their association with euploid embryos. However, the results are controversial, especially in the advanced-aged women group, when the risk of aneuploidy increases significantly. This prospective cohort study evaluated the association between embryo development between day-3 cleavage and day-5 blastocyst stages and euploidy rates, determined using preimplantation genetic testing for aneuploidy (PGT-A). Embryos from women aged 35 years and above who underwent intracytoplasmic sperm injections and PGT-A were studied. Day-3 cleavage-stage embryos were evaluated for their cell number, and day-5 blastocyst-stage embryos were evaluated for their morphological grade. Embryo development from day 3 to day 5 was categorized as either good or poor development and evaluated for its association with the PGT-A results. We evaluated 325 embryos from 101 infertile couples. It was found that 55.17% of blastocysts with good development and 29.83% with poor development were euploid. A significant association was found between embryo development and euploidy rates in advanced-aged women (p < 0.001). Also, there were significantly higher rates of euploid embryos with good blastocyst morphological grades, especially blastocyst expansion grades and trophectoderm grades. In conclusion, embryo morphokinetics shows promising results in predicting euploidy in advanced female age.