Menstrual cramps are pains in the abdomen, pelvis, lower back, and/or thighs that occur before or during menstrual periods. Cramps are not the same as premenstrual syndrome (PMS), a group of symptoms related to the menstrual cycle. PMS usually occurs a week or two before the period and ends when the period starts. Menstrual cramps usually start the day a woman's menstrual period starts, and may last for the entire period.
The medical term for menstrual cramps is dysmenorrhea. Menstrual cramps vary from very mild to quite severe. Most women experience mild to moderate dysmenorrhea from time to time. Severe dysmenorrhea can interfere with a woman's daily activities.
Dysmenorrhea can be either primary or secondary. Primary dysmenorrhea usually begins within a few years after a woman starts her period, usually decreasing in intensity with age. Secondary dysmenorrhea has an underlying pathological cause, such as endometriosis, pelvic inflammatory disease, cervical stenosis, uterine fibroids, or a change in uterine position.
Menstrual cramps are caused by uterine contractions. Between periods, the uterus builds up a lining of blood and tissue in preparation for possible pregnancy. If pregnancy does not occur, a thick uterine lining is not needed, so it is shed at the beginning of the next cycle. As that lining breaks down, it releases hormone-like substances called prostaglandins, which cause uterine contractions. Severity of cramps is related to the prostaglandin level at that time. Women who experience menstrual cramps may produce more prostaglandins than usual or be especially sensitive to their effects. Menstrual cramps usually become less severe over time, but they may not go away completely. Primary dysmenorrhea is uncommon after childbirth.