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

Many experts believe that severe contractions constrict the blood vessels feeding the uterus. The resulting pain can be compared to the angina that occurs when blocked coronary arteries starve portions of the heart of food and oxygen.

Menstrual cramps also may be caused by:

  • Endometriosis. In this painful condition, 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 rarely may be the cause of pain.
  • Adenomyosis. In this condition, the tissue that lines your uterus begins to grow into the muscular walls of the uterus.
  • Pelvic inflammatory disease (PID). This infection of the female reproductive organs is usually caused by sexually transmitted bacteria.
  • Cervical stenosis. In some women, the opening of the cervix may be so small that it impedes menstrual flow, causing a painful increase of pressure within the uterus.
May. 03, 2011