Uterine fibroids are very common. From 20 percent to 40 percent of women age 35 and older have uterine fibroids of a significant size. It is not known why, although genetic variability is thought to be a factor. Fibroid tumors may start in women when they are in their 20s, however, most women do not begin to have symptoms until they are in their late 30s or 40s. Physicians are not able to predict if a fibroid will grow or cause symptoms.
Fibroids can dramatically increase in size during pregnancy .
This is thought to occur because of the increase in estrogen levels during pregnancy. After pregnancy, the fibroids usually shrink back to their pre-pregnancy size. Fibroids typically improve after menopause when the level of estrogen decreases dramatically. Typically, fibroids are first diagnosed during a gynecologic internal exam, which enables the doctor to feel if the uterus is enlarged. The presence of fibroids is most often confirmed by an abdominal ultrasound.