Uterine fibroids are benign (noncancerous) tumors that grow on or within the muscle tissue of the uterus. Approximately 20-40% of women 35 years and older have fibroids. Fibroids are frequent in women of all races, however, they occur more frequently in women of African-American descent. Some statistics indicate that up to 80% of African-American women will develop fibroids. While some women do not experience any symptoms, the location and size of fibroids can cause symptoms that can affect a woman’s quality of life. Of the 600,000 hysterectomies performed annually in the United States, one-third are due to fibroids.

Fibroids are hormonally sensitive, some symptoms are likely to be cyclical, like menstruation. Estrogen levels tend to increase prior to the onset of menopause, which may cause the size of many fibroids to increase. This may cause an increase in symptoms, as well. During menopause, the levels of estrogen decrease dramatically, causing fibroids to shrink. However, women taking hormone replacement therapy (HRT) during menopause may not experience any symptom relief because the estrogen contained in this regime may cause fibroids to enlarge and symptoms to return. 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.

The size of fibroids range from very small (walnut size) to as large as a cantaloupe or even larger. Typically, physicians measure fibroids in terms of the size of the uterus during pregnancy; for example, a very large fibroid can cause the uterus to become the size of a six- or seven-month pregnancy (24-28 weeks). Additionally, there can either be one dominant fibroid or many fibroids.

Fibroids are classified according to their location within the uterus. There are three primary types of fibroids:

  • Subserosal fibroids develop in the outer portion of the uterus and continue to grow outward. These typically do not affect a woman’s menstrual flow, but can cause pain due to their size and pressure on other organs.
  • Intramural fibroids are the most common type and develop within the uterine wall and expand, which makes the uterus feel larger than normal (and may cause “bulk symptoms”). Symptoms associated with intramural fibroids are heavy menstrual flow, pelvic pain, back pain, frequent urination and pressure.
  • Submucosal fibroids develop just under the lining of the uterine cavity. The least common type of fibroid, they often cause symptoms such as very heavy, prolonged menstrual periods.
  • Pedunculated fibroids occur when the fibroid grows on a stalk. Pedunculated fibroids can either extend into the endometrial cavity, or protrude outside of the uterus.

Fibroids may also be referred to as myoma, leiomyoma, leiomyomata, and fibromyoma. A woman may have one or all of these types of fibroids. It is common for a woman to have multiple fibroids and it may be difficult to understand which fibroid is causing her symptoms. Because fibroid tumors are a diffuse disease of the uterus, there are usually more fibroids present than can be detected because of their small size. Even a woman who has only one visible fibroid needs to assume that there are multiple fibroids present when discussing therapy.