Resolving recurrent implantation failure.

Recurrent implantation failure (RIF) continues to represent a difficult clinical challenge. Discussion of its definition continues and the evidence base to support optimal management is weak. Recent studies showing excellent cumulative outcomes following serial transfer have challenged the notion of RIF as anything other than a rare biological phenomenon, as well as the role of the endometrium as a significant factor in RIF. Yet the literature is rich in studies demonstrating how functional endometrial disruption can affect implantation. The emerging understanding of the biosensor role of the endometrium indicates that, like the embryo, its functional integrity exists on a spectrum rather than being simply receptive or non-receptive. The case is made here that it is the combination of embryo and endometrial quality that determines success, and that the one can compensate in part for the other. This paradigm accommodates both the embryo- and endometrium-centric views of implantation, suggesting a new and possibly more fruitful way of considering and investigating RIF.