Causes

During your menstrual period, your uterus contracts to help expel its lining. Hormonelike substances (prostaglandins) involved in pain and inflammation trigger the uterine muscle contractions. Higher levels of prostaglandins are associated with more-severe menstrual cramps.

Menstrual cramps can be caused by:

• Endometriosis. The tissue that lines your uterus becomes implanted outside your uterus, most commonly on your fallopian tubes, ovaries or the tissue lining your pelvis.
• Uterine fibroids. These noncancerous growths in the wall of the uterus can cause pain.
• Adenomyosis. The tissue that lines your uterus begins to grow into the muscular walls of the uterus.
• Pelvic inflammatory disease. This infection of the female reproductive organs is usually caused by sexually transmitted bacteria.
• Cervical stenosis. In some women, the opening of the cervix is small enough to impede menstrual flow, causing a painful increase of pressure within the uterus.