Office of Women's Health

Facts About Uterine Fibroids

What are uterine fibroids?

Uterine fibroids are tumors or lumps made of muscle cells and other tissue that grow within the wall of the uterus. Although fibroids are called “tumors,” they are not cancer. Fibroids may grow as a single tumor or in clusters. A single fibroid can be less than 1 inch in size or can grow to 8 inches across or more. A bunch or cluster of fibroids also can vary in size. Most of the time fibroids grow in women of childbearing age. It is estimated that as many as 77 percent of women of childbearing age could have the condition without knowing it.

Where do uterine fibroids grow?

Doctors put fibroids into three groups based on where they grow, such as just underneath the lining of the uterus, in between the muscles of the uterus, or on the outside of the uterus. Most fibroids grow within the wall of the uterus. Some fibroids grow on stalks (called peduncles) that grow out from the surface of the uterus, or into the cavity of the uterus.

What are the symptoms of uterine fibroids?

Many women don’t feel any symptoms with uterine fibroids. But fibroids can cause the following:

What causes uterine fibroids?

Currently, little is known about what causes uterine fibroids. Scientists have a number of theories, but none of these ideas explains fibroids completely. Most likely, fibroids are the end result of many factors interacting with each other. These factors could be genetic, hormonal, environmental or a combination of all three.

Who gets uterine fibroids?

Most of the time fibroids grow in women of childbearing age, but can be found in women of all ages. Researchers now recognize several risk factors for uterine fibroids:

How are fibroids diagnosed?

Usually, fibroids are found by abdominal or pelvic examination or pelvic ultrasound. To confirm a diagnosis, your health care provider may use imaging technology such as ultrasound, magnetic resonance imaging (MRI), X-rays or a CT “cat”- scan. Sometimes the only way to confirm the diagnosis is through surgery.

How are fibroids treated?

There are several factors to consider when recommending treatment for fibroids.

If a woman has many symptoms or feels pain often, medical therapy may be considered.

If a woman has moderate symptoms, surgery may be the best form of treatment.

Do uterine fibroids lead to cancer?

Uterine fibroids are not cancerous. Fibroids are not associated with cancer. They do not increase your risk for uterine cancer.

More information about uterine fibroids can be obtained by contacting:

Uterine Fibroids

National Institute of Child Health and Human Development

Agency for Healthcare Research and Quality


Uterine Fibroids Fact Sheet

The National Women’s Health Information Center, U.S. Department of Health and Human Services