Optimal Timing of Euploid Day 6 Blastocyst Transfer in Frozen HRT Cycles, Day 6 or Day 7 of Progesterone Administration.

Traditionally the duration of progesterone exposure before embryo transfer has been considered equal for day 5 and day 6 embryos but this may not be the case and warrants further study. The optimal preparation of the endometrium in frozen embryo transfer (FET) cycles is yet to be determined. Synchronization between the embryonic stage and the endometrial window of implantation (WOI) is crucial and progesterone plays a critical role in the WOI (1). Data on the optimal route of administration, the dose and duration of progesterone supplementation before blastocyst transfer are inconsistent (2,3). In view of the current lack of evidence, this study will be of importance.