P-296 Supernumerary blastocysts resulting from abnormal cleavage patterns: freeze or not to freeze? A practical question!
Authors: Entezami F , Marti Vilanova M , Jaldo Garcia J , Pessah C , Gonzalez Marti B 
Published: June 2023

Abstract

Study question
After eSET, the supernumerary blastocysts that showed cleavage anomalies can be vitrified as second choice embryos. Do they display enough implantation chance to be frozen?

Summary answer
No pregnancy was obtained after frozen transfer of blastocysts with direct uneven cleavage and chaotic cleavage. It is not recommended to freeze those spare embryos.

What is known already
The use of time-lapse incubation offers stable culture conditions and provides comprehensive information on dynamic embryo development. Studies found that abnormal cleavage affects the genome of human embryos and can reduce its developmental potential with embryonic arrest. Aneuploidy contributes also to failed implantation. It was also reported that cleavage anomalies such as direct uneven cleavage and chaotic cleavage affect negatively implantation and live birth. Even if the good survival rate of blastocysts after vitrification has dramatically improved clinical outcome after frozen embryo transfer, implantation and live birth are correlated to embryonic ploidy and healthy cellular machinery.

Study design, size, duration
Retrospective qualitative assessment of time-lapse images for 186 vitrified blastocysts resulting from extended culture of 871 embryos showing morphokinetic abnormalities such as direct uneven cleavage first mitosis (DC1), direct cleavage second mitosis (DC2), fast cleavage (FC), complete chaotic cleavage (CC) and multiple anomalies (MA), during 2021-2022 in a single private hospital, and analysis of the clinical outcome after warming and SET.

Participants/materials, setting, methods
From 871 embryos in Embryoscope + (Vitrolife), 445 total blastocysts and 251 top quality were obtained according to Gardner’s grading. 186 of those were vitrified for further transfer. In 5 subgroups of anomalies (DC1, DC2, FC, CC, MA) pregnancy (PR) and ongoing pregnancy rate (OPR) per warming cycle and per transfer were calculated.
The results were compared by SPSS software to overall 2021 center’s results.

Main results and the role of chance
The mean female age was 35.4 ± 0.5 years. From the 186 top quality blastocysts that were vitrified, 96 were warmed in 94 frozen cycles with a survival rate of 98.3%, resulting in 93 SET transfers.
A total of 32 pregnancies were obtained from which 21 were ongoing pregnancies. There was no statistical difference in PR per warming cycle or per transfer, and in OPR per warming cycle or per transfer between the overall study group compared to the center’s annual results 2021: 34.0% vs 40.2%, 34.4% vs 40.1%, 22.3% vs 30.1%, and 22.6% vs 30.7%.
Reasonable PR and OPR per transfer were obtained with blastocysts from DC2, FC and MA patterns, with caution to small sample size: 32.0% and 20.0%, 44.1% and 32.3%, 40.0% and 25.0%. The results were statistically comparable to the center’s annual result.
All the transfers from DC1 and CC pattern failed to achieve a pregnancy.

Limitations, reasons for caution
One limitation of the study was its retrospective nature and the other was the small sample size in each subgroup of anomaly. The results should be confirmed prospectively and should compel the live birth rate after delivery of the ongoing pregnancies obtained during the second semester of 2022.

Wider implications of the findings
Abnormal cleavage patterns such as DC and CC are known to affect negatively implantation and live birth. Deselection of embryos showing these specific patterns could significantly increase successful implantation for the accordingly selected embryos. It is therefore non optimal to freeze the spare blastocysts resulting from these peculiar abnormal patterns.

Trial registration number
NA