Menstrual cramps are caused by contractions in the uterus, which is a muscle. The uterus, the hollow, pear-shaped organ where a baby grows, contracts throughout a woman’s menstrual cycle. If the uterus contracts too strongly, it can press against nearby blood vessels, cutting off the supply of oxygen to the muscle tissue of the uterus. Pain results when part of a muscle briefly loses its supply of oxygen.
It is important to note that menstrual cramps can occur without pain. Some women experience uterine contractions without noticing or with very little discomfort. Many, however, deal with pain each month, caused by long-lasting and intense contractions. The pain of menstrual cramps is experienced when these powerful contractions cut the blood supply to the uterus, leading to a lack of oxygen to the related muscles. Fortunately, the oxygen deprivation, as well as the pain, is only temporary.