Menstruation

The natural, monthly cyclical shedding and discharge of endometrial tissue with blood and uterine secretions in nonpregnant, reproductive-age females, resulting from falling progesterone levels at the end of an ovulatory cycle. Factors that may alter the menstrual cycle are pregnancy, menopause, stress, weight changes, extreme exercise, hormonal imbalances (PCOS), uterine fibroids, endometrial polyps, inflammation (endometriosis).