Embryo and Endometrial Synchrony in Implantation Failure

Abstract

Normal implantation requires synchronous timing between the endometrium and the embryo. A loss of this synchrony—termed dyssynchrony—occurs when the endometrium is not optimally receptive at the time the embryo is ready to implant. This issue related to timing may lead to implantation failure even when the endometrial is capable of being receptive and the embryo was capable of implantation and progressing through pregnancy to delivery. While the traditional view has represented dyssynchrony as pathology attributed singularly to the embryo or the endometrium, it is clear that both entities can have robust reproductive potential in isolation, and the issue lies in the combination of both of these entities at the appropriate time. The timing of the stimulus for secretory transformation may vary from cycle to cycle, and embryonic development can also vary with age. Thus, their respective contribution to dyssynchrony is not always reproducible from cycle to cycle—thus it may not be screened for in advance. All patients undergoing superovulation during IVF are at risk for embryonic-endometrial dyssynchrony based on timing when a critical level of progesterone is attained and the timing of embryonic blastulation.