The optimal FET strategy for the recurrent implantation failure patient: thawing Day 3 embryos and culturing to Day 5 blastocysts

Abstract This study aimed to investigate the optimal frozen embryo transfer (FET) strategy in recurrent implantation failure (RIF) patients with three consecutive failed cleavage embryo implantations. A retrospective analysis of FET cycles performed in our IVF center from January 2018 to August 2020. The FET cycles were classified into three groups according to their FET strategies: thawed day 3 embryo transfer (D3 FET group) (n = 52), thawed blastocyst transfer (D5 FET group) (n = 166), and extended culturing of frozen-thawed day 3 embryos to day 5 blastocysts transfer (D3-5 FET group) (n = 58). The biochemical, clinical pregnancies, implantation, abortion, multiple pregnancy, and live birth were analyzed and compared among the three groups. A total of 43.8% of vitrified-thawed cleavage embryos developed into blastocysts in the D3-5 FET group. Although no statistically significant differences were observed in the number of transferred embryos and grade A embryos among the three groups, the pregnancy outcomes were significantly better in the D3-5 FET group, with higher biochemical, clinical pregnancy, implantation, and live-birth rates (all P < 0.05) in comparison with the D3 FET group. Interestingly, when compared with the D5 FET group, the D3-5 FET group showed a significantly higher implantation rate, although no difference was found in the clinical pregnancy rate and live birth outcomes. Our results suggest that D3-5 FET would be the optimal FET strategy for RIF patients with three repeated consecutive implantation failures by achieving better pregnancy outcomes than the direct D3 FET strategy.