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Fibroids are round growths that develop in the uterus. They are almost always benign, or non-cancerous. Fibroids range in size from as small as a pea to as large as a melon. They are also called leiomyomas or myomas.

Fibroids are very common, affecting an estimated 20 to 50 percent of all women. They are most likely to affect women in their 30s and 40s, and for reasons we don't understand, occur more frequently in African-Americans. Many women with fibroids have family members who also have them.

Some fibroids grow steadily during the reproductive years, while others stay the same size for many years. All fibroids should stop growing after menopause. If your fibroids grow after menopause, you should consult your doctor.

Usually, fibroids cause no symptoms and don't require treatment. But if symptoms occur, you should seek medical attention.

Types of fibroids

Fibroids can grow in different parts of the uterus:

  • Pedunculated fibroids are attached to the uterine wall by stalks.
  • Subserosal fibroids extend outward from the uterine wall.
  • Submucosal fibroids expand from the uterine wall into the uterine cavity.
  • Intramural fibroids develop within the uterine wall.

Different types of fibroids are associated with different symptoms. For example, submucosal fibroids typically cause heavy periods. In contrast, subserosal fibroids are more likely to push against the bladder, causing frequent urination.

Causes of fibroids

Doctors and medical researchers do not know what causes fibroids to develop. There is evidence that the female hormones, estrogen and progesterone, can make them grow. During pregnancy, when the hormone levels are high, fibroids tend to increase in size. After menopause, when the hormone levels are low, fibroids stop growing and may become smaller.

Our approach to fibroids

There are many effective ways to treat uterine fibroids. UCSF offers a wide range of treatments, including innovative and minimally invasive surgical techniques. When needed, we coordinate care with other experts at UCSF, such as fertility doctors and obstetricians who specialize in high-risk pregnancy.

The best treatment choice for each woman depends on personal preference as well as the size and location of her fibroids. We believe that empowering women with knowledge is an important part of the healing process, and encourage each patient to participate in choosing the best treatment option for her.

UCSF Health medical specialists have reviewed this information. It is for educational purposes only and is not intended to replace the advice of your doctor or other health care provider. We encourage you to discuss any questions or concerns you may have with your provider.