Human chorionic gonadotropin: does it affect human endometrial morphology in vivo?

Human chorionic gonadotropin (hCG) is widely used as a surrogate to luteinizing hormone (LH) to trigger ovulation in controlled ovarian hyperstimulation (COH). Yet this molecule may exert direct effects on the endometrium. These effects, not mediated by ovarian hormones, are probably a consequence of stimulation of endometrial hCG/LH receptors. Because the half-life of hCG differs markedly from that of LH, possible pharmacological effects of hCG on the endometrium could alter endometrial receptivity in COH. Arguments supporting a clinical action of gonadotropins, and hCG in particular, on the endometrium abound. Notably, evidence has been reported of decidualization of stromal cells of the human endometrium in vitro as a result of exposure to gonadotropins, including hCG. The present article discusses, from a clinical standpoint, the main basis supporting the hypothesis that hCG administration as commonly used in infertility treatments may exert direct effects in vivo on endometrial histology and partake in endometrial transformations of the luteal phase. Preliminary results suggest that endometrial effects of hCG exist in vivo and should be taken into account when assessing the endometrial effects of hormones.