A woman’s menstrual cycle is the shedding of the endometrium, which occurs when the lining of the uterus loses its hormonal protection due to a drop in the levels of estrogen and progesterone in the woman’s body prior to menstruation. This is not the case after pregnancy. After pregnancy, a woman’s corpus luteum is transformed into the corpus luteum gestationis by the action of embryonic chorionic gonadotropin and increases in size. The corpus luteum gestationis secretes estrogen and progesterone, and the amount of these hormones is significantly increased during pregnancy. The lining of the uterus does not shed with the support of these two hormones, so there is no menstrual flow. If the hormone level in the woman’s body is relatively low, there may be a small amount of bleeding, which is called preeclampsia.