Fibroids Overview

Fibroids are masses of noncancerous tissue that may grow in your uterus. Some women have one one. Others have several. They can be as small as a pea or as large as an orange.

The word “fibroid” is a misnomer, says women’s health specialist Susan Lark, M.D., of Los Altos, California. “It implies that these tumors arise from fibrous tissue. Actually, they grow from the smooth muscle layer of the uterus, the myometrium. It lies under the uterine lining, the endometrium, which bleeds each month during your period. The correct medical term for fibrois is ‘myoma’ or ‘leiomyoma.'”

About one-quarter of women over 35 have fibroids, though half never know it. For reasons that remain unclear, they typically develop in your late thirties or forties, and often grow large around your mid-forties, as you become “perimenopausal,” the time when you begin the many-year process of menopause.

Fibroids tend to run in families. Any woman can develop them, but compared with whites, African-Americans have about three times the risk. No one knows why.

Most fibroid cause no symptoms. You typically learn you have them when your doctor discovers them during a routine pelvic exam. On the other hand, some fibroids cause problems, notably unusually heavy menstrual flow. Why? Uterine muscle contractions play an important role in limiting menstrual flow, and fibroids may interfere with this.

If your flow is heavy enough for long enough, your fibroids might give you iron-deficiency anemia. Fibroids may also cause spotting between periods, dull pain or feelings of fullness or pressure in your lower abdomen or back. If they press on your bladder or rectum, you might develop urinary or bowel symptoms. If they develop near your cervix, you might feel discomfort on intercourse. Fibroids can also contribute to infertility or miscarriage. Occasionally, you might feel sudden sharp pain in your lower abdomen. That might be a medical emergency (see Red Flags).

Fibroids often cause your uterus to enlarge, as if you were pregnant. Doctors often describe fibroids as producing a “12-to14-week-size uterus,” or some other figure related to pregnancy.

The cause of fibroids is a mystery, but exposure to estrogen makes them grow quickly, Dr. Lark explains. Your estrogen level rises considerably during pregnancy, and any fibroids you have may balloon, which is why they’re associated with miscarriage. Estrogen also appears to explain why fibroids often grow quite large in the years preceding menopause. Gerson Weiss, M.D., chair of obstetrics and gynecology at the New Jersey Medical School in Newark theorizes that when you’re perimenopausal, your estrogen level spikes upward, while othe hormones that dampen estrogen’s effects remain low. Then, as your estrogen level declines after menopause, fibroids usually shrink.