Uterine fibroids are benign (noncancerous) growths or tumors found in the uterus. Also known as leiomyomas or myomas, they can trigger a variety of symptoms, depending on their location, size and proximity to nearby pelvic organs.

The cause of uterine fibroids is unknown, but family history is a risk factor for their development. Race also seems to play a role in who develops fibroids. In fact, Black women are two to three times more likely to experience the growths than women of other races.

These growths can vary in size; some are as small as a seed (less than 1 centimeter, or 0.39 inches), while larger fibroids may grow to the size of a grapefruit (around 10 centimeters, or 3.9 inches). What’s more, many of them can sometimes cluster together.

Fibroids can undergo sudden growth spurts, or they may become enlarged over time. In many cases, the change in size is due to an abundance of hormones, such as estrogen, in the body. The presence of high levels of hormones—as are seen during pregnancy—helps fibroids grow bigger. Conversely, during menopause, fibroids may shrink due to decreasing hormone levels. When this occurs, fibroid symptoms are more likely to improve.

Despite their scary appearance, fibroids rarely morph into cancerous growths. Made up of smooth muscle tissue, these benign tumors are dense and rounded and may be classified into several types.

Fibroids that form outside the uterus, or womb, are called subserosal fibroids. These may rest beneath the membrane that lines the outside of the uterus. Those that form inside the cavity of the uterus are known as submucosal fibroids and lie beneath the inner lining of the womb. Fibroids that form in the walls of the uterus are called intramural fibroids. Sometimes, fibroids are attached to the outside of the uterus by a stalk of tissue, or they may extend inside the uterine cavity. These are classified as pedunculated fibroids and resemble mushrooms.

Approximately 40% to 80% of women of childbearing age develop fibroids. Some women are unaware they have fibroids because they don’t feel any pain or pressure in their pelvic area or on nearby organs or experience heavy menstrual bleeding.

Although fibroids can occur at any age, they are commonly found in women between 30 and 40 years old. Generally, 70% to 80% of all women develop these tumors by age 50. African-American women are more often affected by fibroids; additionally, in Black women, fibroids tend to appear at a younger age and grow more quickly.

The following common symptoms may indicate the presence of uterine fibroids:

  • Lower back pain
  • Pain in the abdomen (cramps)
  • Heavy menstruation
  • Anemia
  • Painful periods
  • Reproduction problems, such as infertility, miscarriages and early labor
  • Painful sex
  • Vaginal bleeding when not menstruating
  • Urinating frequently or problems urinating.

Because women may lack symptoms, uterine fibroids are often discovered during a routine gynecological pelvic exam or through image studies. In addition, larger fibroids can cause pain and discomfort, which is usually the first indication that something is wrong. Pain and excessive bleeding must be evaluated by a doctor. Excessive bleeding during a woman’s menstrual cycle can result in anemia, which, in turn, may lead to fatigue and weakness.

Additionally, fibroids can cause a woman to bleed in between periods. Some women may also develop a craving for ice, starch or dirt, a condition known as pica. This desire is linked to anemia, which causes a shortage of the healthy red blood cells that disperse oxygen to the body’s organs. If fibroids begin to grow rapidly or become enlarged during menopause, experts recommend that women see a doctor immediately.