P-187 Post-thaw embryo quality is not predictive of live birth rates in frozen embryo transfer cycles: a retrospective cohort study
Authors: Wu C , Nguyen V , Leveille M.C , Gale J 
Published: June 2022

Abstract

Study question
To determine whether post-thaw change in embryo quality is associated with live birth outcomes.

Summary answer
Post-thaw embryo morphology is not predictive of live birth rates in single frozen embryo transfer cycles.

What is known already
Embryo quality is typically evaluated via morphological assessment of embryos based on the Gardner criteria. For medical or elective reasons, embryos are commonly frozen for future use through the vitrification process. Research has shown that embryo quality pre-vitrification correlates highly with freeze-thaw survival, implantation, pregnancy, and subsequent live birth rates. Good-quality embryos are therefore more likely to be selected for vitrification. However, it is not unusual to find a decline in the quality of these vitrified embryos upon thawing them for embryo transfer.

Study design, size, duration
We retrospectively identified a patient cohort based out of the Ottawa Fertility Centre in Ottawa, Ontario, Canada, between 2016 and 2020.

Participants/materials, setting, methods
Frozen single embryo transfer (FET) cycles involving good-quality expanded blastocysts deriving from autologous oocytes were selected for inclusion. We compared FET cycles involving good post-thaw embryo quality to those with worsened/poor post-thaw embryo quality. The primary outcome was live birth after FET. Secondary outcomes included rates of positive serum human chorionic gonadotropin, clinical intrauterine pregnancy, miscarriage, and ectopic pregnancy. We fit a multivariate logistic regression model, adjusting for patient and cycle characteristics.

Main results and the role of chance
A total of 962 single FET cycles were analyzed. There were 826 embryos that preserved their pre-vitrification quality post-thaw and 136 embryos that exhibited poorer quality on post-thaw assessment. Baseline characteristics were mostly comparable between the two groups under study. In the multivariate regression model, the adjusted odds of live birth was not significantly different in the group with good post-thaw embryo quality compared to that in the group with worse/poor post-thaw embryo quality (odds ratio [OR] 1.30, 95% confidence interval [CI] 0.86-1.96, p = 0.21). Similarly, no significant associations were found between post-thaw embryo quality and the secondary outcomes of positive BhCG (OR 1.19, 95% CI 0.81-1.75), clinical intrauterine pregnancy (OR 1.29, 95% CI 0.87-1.87), miscarriage (OR 0.97, 95% CI 0.53-1.77), and ectopic pregnancy rates (OR 0.41, 95% CI 0.14-1.24).

Limitations, reasons for caution
Although a multivariate regression model was used to adjust for clinically relevant confounders, there remains the possibility for residual confounding given the observational nature of our study.

Wider implications of the findings
The results of our study suggest that, after adjusting for patient and cycle characteristics, post-thaw embryo quality does not impact live birth outcomes.

Trial registration number
Not applicable