Endometrial receptivity describes the intricate process undertaken by the uterine lining to prepare for the implantation of an embryo. While embryo development and endometrial preparation are concurrent yet independent processes, their synchronization is critical to the success of embryo apposition, adhesion, invasion, and further ongoing pregnancy. The accepted definition of endometrial receptivity is "the period of endometrial maturation during which the trophectoderm of the blastocyst can attach to the endometrial epithelial cells and subsequently invade the endometrial stroma and vasculature." The limited period of optimal endometrial receptivity in which the endometrium is ready to receive an embryo, paired with an embryo's readiness to the implant, is commonly referred to as the "window of implantation" and is generally detected between days 20 and 24 of a normal 28-day menstrual cycle.
Many molecular pathways involve hormones, adhesion molecules, cytokines, and growth factors acting in concert to create a synchronous window of implantation. When synchrony is lost or receptivity is not achieved, the consequence is early pregnancy loss or infertility. This review aims to define endometrial receptivity, describe the critical factors contributing to the development and function of a receptive endometrium, review the causes and consequences of a non-receptive endometrium, and discuss the available technologies for diagnosing and treating the potentially defective endometrium in infertility patients.
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