Uterine receptivity and the ramifications of ovarian stimulation on endometrial function

Controlled ovarian stimulation (COS) is widely used in assisted reproduction techniques (ART). However, hormonal treatment induces endometrial alterations that may alter implantation rates compared with natural cycles. Endometrial alterations have been observed by histological and biochemical techniques. The recent developments in functional genomics have provided objective tools to analyze the endometrium in natural cycles and evaluate the impact of COS protocols in endometrial development. This article describes the fundamental aspects of endometrial receptivity in natural cycles and reports how COS affects the morphology, biochemistry, and the genomic pattern of the endometrium.