Morula transfer achieves better clinical outcomes than post-thawed cleavage embryos after overnight culture in frozen embryo transfer (FET) cycles.

purposeThis study aimed to investigate the clinical outcomes of morula stage transfer derived from post-thawed cleavage embryos undergoing overnight culture in frozen embryo transfer (FET) cycles.

methodsWe performed a retrospective study that included 392 FET cycles with 784 thawed embryos undergoing overnight culture between January 2014 and December 2018. Embryos were divided into three groups in terms of their status: 8-16 cells without morula (group I), one morula (group II), and two morulae (group III). The clinical outcomes of these cycles were then compared between the three groups. Logistic regression analysis was performed to control for confounders.

resultsGroup III was associated with a significantly higher clinical pregnancy rate (odds ratio [OR] 2.35; 95% confidence interval [CI] 1.29-4.27; P = 0.005), implantation rate (OR 3.00; CI 1.75-5.16; P < 0.001), multiple pregnancy rate (OR 4.91; CI 2.11-11.40; P < 0.001), and live birth rate (OR 1.96; CI 1.10-3.49; P = 0.022) than group I. Group II had a higher live birth rate than group I after adjustment (OR 1.70; CI 1.04-2.79; P = 0.035). There was no difference in the rate of premature delivery when compared across the three groups after adjustment.

conclusionThe transfer of morula stage embryos following the overnight culture of post-thawed cleavage embryos led to an improvement in the clinical outcomes of FET cycles. It is important to reduce the number of morula embryos transferred in order to achieve a singleton pregnancy.