In more than 8 out of 10 cases, there is no serious cause for painful menstrual periods (dysmenorrhoea). Although distressing, they are merely the way in which a woman, and her uterus, copes with menstruation.
The uterus mainly consists of powerful muscle fibres, which should only come into use during the delivery of a baby, and to a minor extent when blood and the unused lining of the uterus is expelled in the monthly menstrual period. Period pain is usually caused by excessive spasms of these muscles in the uterus, but sometimes may be due to other medical problems.
During the menopause, the natural sex hormones produced by the ovaries, may be produced irregularly and in greater quantities, leading to an increased build up of the uterine lining during the month, or excessive stimulation of the uterine muscles during a period.
An intrauterine contraceptive device (IUD) may irritate the uterus to trigger more powerful contractions than usual.
Salpingitis (infection of the fallopian tubes), often by sexually transmitted diseases, may result in the tubes becoming blocked and painful. Pelvic inflammatory disease is a more widespread infection of the organs within the pelvis. During a period, contractions of the uterus may irritate these infected organs to cause pain.
Endometriosis is a disease in which the cells that normally line the inside of the uterus become displaced, and move through the fallopian tubes to settle around the ovary, in the tubes themselves, or on other organs in the belly. In these abnormal positions they proliferate, and when a menstrual period occurs, they bleed as though they were still in the uterus. This results in pain, adhesions, damage to the organs they are attached to, and infertility.
Fibroids are hard balls of fibrous tissue that form in the muscular wall of the uterus, often after pregnancy. They can distort the shape of the uterus to cause pain when the uterus contracts during a period or orgasm.
The uterus is normally bent forwards at about 60° to the vagina. In some women, the uterus is straighter, or bent backwards (retroverted). These women seem to suffer from more painful periods.
Other causes of dysmenorrhoea include a prolapse of the uterus (uterus slips down into the vagina), pelvic congestion syndrome (veins in the pelvis become dilated), narrowing of the cervix after surgery, adhesions and tumours, polyps or cancers of the uterus or surrounding organs.