The shedding of the endometrium is mainly caused by a decrease in estrogen and progesterone levels prior to menstruation. With lower estrogen and progesterone levels, the endometrium loses the support of high hormone levels, so exfoliative bleeding occurs. Normally, the endometrium changes with the menstrual cycle, and this change is mainly related to the changes in estrogen and progesterone levels in the patient’s body. After the end of the patient’s period, follicle stimulating hormone levels will be very high, so it will stimulate the patient’s ovaries to develop follicles. When the follicles grow, the patient’s estrogen level increases, so it stimulates the patient’s endometrium to undergo hyperplasia. When the patient ovulates, the patient’s estrogen level will decrease and the patient’s progesterone level will increase. Progesterone inhibits the excessive proliferation of the endometrium, so that the endometrium has a proliferative phase that changes to a secretory phase, mainly in preparation for the fertilization of the egg. When the patient does not conceive, the estrogen and progesterone levels will drop, so the patient’s endometrium will peel off and she will have her period.