A menstrual disorder is any condition that interferes with the normal menstrual cycle, causing pain, unusually heavy or light bleeding, or missed periods. Normal vaginal bleeding is the periodic blood that flows as a discharge from the woman’s uterus. Normal vaginal bleeding is also called menorrhea. The process by which menorrhea occurs is called menstruation. Abnormal vaginal bleeding is a flow of blood from the vagina that occurs either at the wrong time during the month or in inappropriate amounts. These include amenorrhea, or the cessation of menstruation, menorrhagia, or heavy bleeding, and dysmenorrhea, or severe menstrual cramps. Nearly every woman experiences one or more of these menstrual irregularities in her lifetime. PCOS (polycystic ovarian syndrome) is a major cause for irregular menstruation.