Sequential Transfer of Blastocysts on Day 5 and Day 6 in Patients with Repeated Implantation Failure in Frozen Embryo Transfer Cycle.

The aim of this study was to evaluate which frozen embryo transfer (FET) strategy benefits the recurrent implantation failure (RIF) population. A retrospective study of 336 women with RIF was performed from July 2020 to October 2023. The patients were divided into three groups according to the FET protocol. The three FET protocols included transferring a blastocyst on both days 5 and 6 (Group 1, n = 138); transferring a cleavage-stage embryo on day 3 and a blastocyst on day 5 (Group 2, n = 55); and transferring double blastocysts on day 5 (Group 3, n = 143).The sequential day 5 and day 6 blastocyst ET strategy significantly improved in vitro fertilization success rates compared with those of both the traditional double-blastocyst day 5 transfer strategy and the strategy involving one cleavage-stage embryo transfer on day 3 and one blastocyst transfer on day 5 in RIF patients. Compared with those observed in Day 5 double-blastocyst transfer, the rates of clinical pregnancy and implantation increased (51.75% vs. 64.49%, P < 0.001 and 37.06% vs. 41.3%, P = 0.005, respectively), while the rates of biochemical pregnancy and multiple gestation decreased (18.18% vs. 12.32%, P = 0.006 and 43.24% vs. 28.09%, P = 0.044, respectively) with the new protocol.Blastocysts from sequential embryo transfer on day 5 and day 6 were more effective than those from the traditional FET protocol at improving pregnancy outcomes and lowering the multiple pregnancy rate in RIF patients. When only one or zero good-quality blastocysts are available, sequential blastocyst ET on days 5 and 6 should be considered.