Role of Human Chorionic Gonadotropin. The trophoblastic cells secretes human chorionic gonadotropin hormone which has properties similar to those luteinizing hormone (LH) of the pituitary gland. It takes over the function of pituitary LH during pregnancy. HCG maintains the corpus luteum and stimulates it to secrete progesterone. The latter maintains the endometrium of the uterus and causes it to grow throughout pregnancy. This also prevent menstruation. Progesterone also causes increased secretion of mucus in the cervix of the uterus that forms a protective plug during pregnancy