P-163 Effects of Early Modes of Cell Division on Blastocyst Ploidy
Authors: Mizobe Y , Kuwatsuru Y , Kuroki Y , Fukumoto Y , Tokudome M , Moewaki H , Tabira M , Iwakawa T , Takeuchi K 
Published: June 2022

Abstract

Study question
Abnormal cleavage (AC) has been confirmed at early development. We performed an NGS analysis on AC-derived blastocysts to investigate ploidy of the resulting embryos.

Summary answer
Group in which AC occurred during second division showed significantly higher rates for embryos appropriate for transfer than group where AC occurred during first division.

What is known already
Early division is important in embryogenesis and serves as an indicator of subsequent embryonic development. The occurrence of AC during early development can be identified with the advent of the time-lapse incubator, which in turn has led to difficulties in determining whether such AC-derived blastocysts can be used embryo transfer. In this study, we performed NGS analysis on AC-derived blastocysts to investigate the ploidy of the resulting embryos.

Study design, size, duration
The subjects comprised women from whom oocytes were collected for NGS analysis from January 2019 to November 2021. Retrospective analysis was performed using a time-lapse system (EmbryoScope+). Embryos were categorized into two groups: those with abnormal divisions observed during the first and second divisions and those in which normal divisions were observed in the same cycle.

Participants/materials, setting, methods
The group with AC observed was designated the AC group and the other with normal divisions as the Normal Cleavage (NC) group. Within the AC group, the subgroup with AC observed during first division was designated as the First (AC-F) group and the subgroup with AC observed during second division as the Second (AC-S) group for comparing the acquisition rates for euploidy embryos and embryos appropriate for transfer.

Main results and the role of chance
The AC group (17.3%) showed a significantly lower rate of good blastocyst formation than did the NC group (53.4%) (P &lt; 0.01). The cutoff point for mosaicism was defined as &gt; 20% of abnormal cells. Percentage &lt;20 were classified as normal (euploid); &gt;80, abnormal (aneuploidy); and 20-80, mosaic. Using a cutoff of 50% to differentiate ‘‘low’’ mosaics from ‘‘high’’ mosaics. There was no difference between the two groups in the acquisition rates for euploidy embryos (30.8-35.1%) and the embryos appropriate for transfer, including low-mosaic ones (44.3-46.1%). There also was no difference in the acquisition rates for euploidy embryos (24.0-37.0%) between the AC-F and AC-S groups. However, the AC-S group (59.3%) showed significantly higher acquisition rates than the AC-F group (32.0%) for the embryos appropriate for transfer, including low-mosaic ones (P &lt; 0.05).

Limitations, reasons for caution
PGT-A is still under clinical research in Japan.

Wider implications of the findings
The group in which AC occurred during second division showed significantly higher acquisition rates for the embryos appropriate for transfer than the group in which AC occurred during first division. This indicates that the most important factor for identifying euploidy embryos is going through the two-cell phase during first division.

Trial registration number
not applicable