Definition of Mittelschmerz:

Mittelschmerz is one-sided lower-abdominal pain that occurs in women at or around the time of ovulation.

Causes, incidence, and risk factors:

About 20% of women experience mittelschmerz, or pain associated with ovulation. The pain may occur just before, during, or after ovulation.

There are several explanations for the cause of this pain. Just prior to ovulation, follicle growth may stretch the surface of the ovary, causing pain. At the time of ovulation, fluid or blood is released from the ruptured egg follicle and may cause irritation of the abdominal lining. Mittelschmerz may be felt on one side one month, then switch to the opposite side the next month, or it may be felt on the same side for several months in succession.

The pain is not harmful and does not signify the presence of disease. In fact, women who feel this pain may be at an advantage when planning or trying to avoid pregnancy. A woman is most likely to become pregnant just before ovulation, on the day of ovulation, or immediately after ovulation. However, birth control methods that rely solely on predicting ovulation are far from completely reliable.