Extended Culture of Day 3 to Day 5 Frozen Thawed Day 3 Embryos Versus Day 5 Frozen-Thawed Embryos

Cryopreservation of embryos and oocytes has become routine in assisted reproduction technology (ART). Live birth rates following frozen embryo transfers have increased significantly. Data show that cryopreservation has significant improved survival rates and cumulative pregnancy rates, as well as the safety of ART . Embryo cryopreservation has become a cornerstone in ART. With improved vitrification techniques. Frozen embryos transfer (FET) shows equal or even higher implantation and pregnancy rates than do fresh embryo transfers ART Previous studies show equal or even superior outcomes regarding pregnancy and live birth rates with frozen versus fresh embryo transfer Cryopreserve all embryos have increased substantially in recent years, and according to the recent trend of a freeze-all strategy. This study aims to answer a clinical question encountered in daily practice regarding at what stage embryos should be frozen.