Current studies on human implantation: a brief overview

Abstract

Embryo implantation involves a series of complex interactions between the developing embryo and the maternal endometrium. Results of studies with animal models suggest that the uterus must undergo a series of morphological and biochemical changes, mediated primarily by oestrogen and progesterone, before it becomes receptive for successful implantation. At present there is little understanding of the endometrial changes required to achieve endometrial receptivity for implantation in the human. It appears that control of receptivity is not as stringent in the human as in some other species, with IVF data suggesting that the duration of receptivity is at least 4 days, and that successful implantation can occur under a relatively wide range of morphological and ultrastructural conditions. Research on the later stages of implantation, including embryo positioning within the uterus, attachment and invasion, has been almost non-existent in the human. Further studies are critical for a better understanding of this complex process, although human studies will always be limited by ethical constraints.