Uterine fibroids are benign (not cancer) growths in the uterus. They occur in about 20-25% of all women. Most women who have fibroids are not aware of them because the growths can remain small and not cause symptoms. In other women they can cause problems because of their size, number, and location.
Fibroids are most common in women aged 30-40, but they can occur at any age. They are also called leiomyomas or myomas. Although uterine fibroids are quite common, little is known about what causes them. They develop from the cells that make up the muscle of the uterus. The female hormone estrogen seems to increase their growth. The levels of estrogen in the body can rise or fall based on natural events. For instance, pregnancy causes an increase in estrogen and menopause causes a decrease. Medications also may cause a change in estrogen levels. Fibroids occur more often in black women than in white women.
The size, shape, and location of fibroids can vary greatly. Fibroids can range in size from small, pea-sized growths to large ones that may be more than 15cm wide. They may appear inside the uterus on its outer surface (subserous), within its wall (intramural), or under the endometrium protruding into the uterine cavity (submucosal). Some of them if they grow, may distort the inside as well as the outside of the uterus. A very large fibroid may cause swelling of the abdomen. This can make it hard to do a thorough pelvic exam. A woman may have only one fibroid or many of varying sizes. Whether they will occur singly or in groups, is hard to predict. They may remain very small for a long time, suddenly grow rapidly, or grow slowly over a number of years. Because it is hard to predict their growth, fibroids can be hard to treat.