Timing endometrial receptivity in the transfer cycle—without compromising it—is a major goal.
Successful embryo implantation in IVF cycles requires a fully competent embryo, optimal ET technique, and a receptive endometrium. Whereas establishment of the former two has significantly improved over time, timing endometrial receptivity is still a challenge. The maximal window of implantation (WOI) lasts between 24 and 48 hours.
Transferring embryos into dyssynchronous endometrium decreases the implantation rate and increases the miscarriage rate. The inability to determine maximal endometrial receptivity is one of the major reasons implantation rates in assisted reproductive technologies have plateaued and more frozen ET (FET) cycles are performed to allow transfer when development of the embryo is considered synchronized with that of the endometrium.