Obesity and PCOS: the effect of metabolic derangements on endometrial receptivity at the time of implantation.

Successful embryonic implantation is the result of a receptive endometrium, a functional embryo at the blastocyst stage and a synchronized dialog between maternal and embryonic tissues. Successful implantation requires the endometrium to undergo steroid-dependent change during each menstrual cycle, exhibiting a short period of embryonic receptivity known as the window of implantation. The term "endometrial receptivity" was introduced to define the state of the endometrium during the window of implantation. It refers to the ability of the endometrium to undergo changes that will allow the blastocyst to attach, penetrate, and induce localized changes in the endometrial stroma. These changes are metabolically demanding, and glucose metabolism has been proven to be important for the preparation of the endometrium for embryo implantation. Obesity and polycystic ovary syndrome (PCOS) represent 2 common metabolic disorders that are associated with subfertility. The aim of this review is to summarize the effect of obesity and PCOS on endometrial receptivity at the time of implantation. Focus will be on metabolic alterations that regulate decidualization, including glucose metabolism, hyperinsulinemia, and hyperandrogenism.