Implantation

Abstract

Clearly, the development of a receptive uterus and the ongoing interaction of the implanting embryo and the endometrium is quite complex. Intercellular communication exists within the cell types of the endometrium in response to steroid hormone secretion by the developing follicle. This initiates the process of uterine receptivity. Coincident with this process, the endometrium increases vascular permeability, and with the arrival of the implanting blastocyst, a local inflammatory response is established. The embryo may itself be the initiator of this response. The subsequent rapid growth of the trophoblast early in implantation may be in response to endogenous growth factors. Also, the penetration of the basement membrane and invasion of the endometrial stroma almost assuredly involve the local production of proteases by the embryo. Much work remains to be done to fully understand this critical step in human reproduction.