Effect of the time for embryo transfer from oocyte retrieval on clinical outcomes in freeze-all cycles: a retrospective cohort study

Purpose: To identify the optimal time for the frozen embryo transfer (FET) after oocyte retrieval in freeze-all cycles. Methods: A retrospective analysis of 977 patients was performed. Implantation, clinical pregnancy and live birth rates were analyzed. Results: No significant difference was found between the first FET performed in the first menstrual cycle group and performed within the subsequent menstrual cycle group in terms of implantation, pregnancy and live birth rates. To rule out the effect of endometrial thickness, a hierarchical analysis was performed. There were no differences between groups for pregnancy, multiple pregnancy and live birth rates for all ranges of endometrial thickness. Conclusions: The first FET should be performed once the endometrial thickness has been prepared well rather than delaying until the subsequent menstrual cycles.