Redefining Endometrial Receptivity

However, the notion of receptivity as a static state in which the tissue is poised, frozen in time, awaiting the arrival of an adequately developed embryo, is naïve. An integrative definition of receptivity must embrace communication between maternal and embryonic tissues. At receptivity, the endometrium has reached a point at which negotiation can begin that may or may not lead to successful implantation, placentation, development and growth of a viable conceptus. Global transcriptomic comparison of receptive and non-receptive endometrium has undergone refinement to identify signalling pathways that may operate in different cell compartments (5). The Wnt pathway is operative at several stages of implantation including blastocyst activation, juxtacrine signalling at the epithelial stages and later interaction with deciduas (6). Chemokine pathways are implicated (7) as are prostaglandins (8), cannabinoids (9), lysophosphatidic acid (10), HB-EGF (11) and others. The idea that the initial interaction between trophectoderm and apical uterine epithelium might either mediate or impede a molecular cascade leading to implantation (12-16) came from observations suggesting that embryos would attach freely to stromal cells or extracellular matrix (17), but not to epithelial cells outside the receptive phase, and led to a hypothesis that the luminal epithelium resists attachment until the mid-secretory phase. l ( ) : 1–6