Research progress of two-step sequential embryo transfer strategy in in vitro fertilization-embryo transfer cycles

In in vitro fertilization-embryo transfer, thedialoguebetween the embryo and the endometrium is critical for embryonic planting, given the high quality of the embryo and good endometrial receptivity. Embryos were transplanted twice in the same cycle, maximizing the chance of the embryos finding and recognizing the synchrony of the uterus with theplanting windowof the embryos, resulting in higher planting rates. This article elaborates and summarizes the day 2 (D2)/D5 or D3/D5 two-step (sequential) transplantation strategy from the aspects of application progress, applicable population, mechanism of action, safety, and future direction, Which has important clinical application value for the reproductive doctor to select the best transplantation decision, improve the embryo utilization and obtain a higher reference rate of clinical pregnancy. Key words: Two-step (sequential) transplantation; Blastocyst; Pregnancy rate; Implantation rate