In most women, various physical changes are brought about by fluctuations in hormone levels during the menstrual cycle. This includes muscle contractions of the uterus (menstrual cramping) that can precede or accompany menstruation. Many women experience painful cramps, also known as dysmenorrhea, during menstruation. Among adult women, that pain is severe enough to affect daily activity in only 2%–28%. Severe symptoms that disrupt daily activities and functioning may be diagnosed as a premenstrual dysphoric disorder. These symptoms can be severe enough to affect a person’s performance at work, school, and in everyday activities in a small percentage of women.