In primary dysmenorrhea, there is no underlying gynecologic problem causing the pain. This type of cramping may begin within six months to a year following menarche (the beginning of menstruation), the time when a girl starts having menstrual periods. Menstrual cramps typically do not begin until ovulatory menstrual cycles (when an egg is released from the ovaries) occur, and actual menstrual bleeding usually begins before the onset of ovulation. Therefore, an adolescent girl may not experience dysmenorrhea until months to years following the onset of menstruation.
Each month, the inner lining of the uterus (the endometrium) builds up in preparation for a possible pregnancy. After ovulation, if the egg is not fertilized by a sperm, no pregnancy will result and the current lining of the uterus is no longer needed. The woman's estrogen and progesterone hormone levels decline, and the lining of the uterus becomes swollen and dies. It is then shed and will be replaced by a new lining in the next monthly cycle.
When the old uterine lining begins to break down, molecular compounds called prostaglandins are released. These compounds cause the muscles of the uterus to contract. When the uterine muscles contract, they constrict the blood supply (vasoconstriction) to the endometrium. This contraction blocks the delivery of oxygen to the tissue of the endometrium which, in turn, breaks down and dies. After the death of this tissue, the uterine contractions literally squeeze the old endometrial tissue through the cervix and out of the body by way of the vagina. Other substances known as leukotrienes, which are chemicals that play a role in the inflammatory response, are also elevated at this time and may be related to the development of menstrual cramp.
