Methods: In this cohort retrospective study, 366 FET cycles were divided into two groups: Group A, the embryos were warmed one day before transfer, and were cultured overnight; Group B, the embryos were warmed on the same day of transfer, at least were cultured 1 h before embryo transfer (ET). Chemical and clinical pregnancy and live birth rates were compared between two groups.
Results: The chemical pregnancy was higher in group A than B (37.9% versus 28.9%), but this difference was not significant (P = 0.07). Clinical pregnancy (30.8% versus 24.1%) and live birth (19.8% versus 22.05%) were similar in group A and B, (P = 0.15), and (P = 0.8). Conclusion: In conclusion, overnight culture and confirmation of mitosis resumption was not essential for FET cycles in vitrification method.