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What are Uterine Fibroids?

December 6, 2010

Fibroids are benign growths in the muscle walls of the uterus. Another medical term for fibroids is “leiomyoma” or just “myoma”. Fibroids can grow as a single tumor, or there can be many of them in the uterus. They can be as small as an apple seed or as big as a grapefruit.

There are several different fibroid types, classified by where they grow:

  • on a stalk either inside or outside the uterus (referred to as “pedunculated”)
  • just below the lining of the uterus (referred to as “submucosal”)
  • in the middle of the uterine wall (referred to as “intramural”)
  • under the outer covering of the uterus (referred to as “subserousal”)


There are factors that can increase a woman’s risk of developing fibroids.

  • Age. Fibroids become more common as women age, especially during the 30s and 40s through menopause. After menopause, fibroids usually shrink.
  • Family history. Having a family member with fibroids increases your risk. If a woman’s mother had fibroids, her risk of having them is about three times higher than average.
  • Ethnic origin. 80% of African American women and 70% of Caucasian, Hispanic and Asian women develop uterine fibroids by the time they are 50.
  • Obesity. Women who are overweight are at higher risk for fibroids. For very heavy women, the risk is two to three times greater than average.
  • Eating habits. Eating a lot of red meat (e.g., beef) and ham is linked with a higher risk of fibroids. Eating plenty of green vegetables seems to protect women from developing fibroids.

In about a third of women who have them, fibroids grow large enough to be detected by a physician during a gynecological exam. Even among these women, 70% will never have symptoms or require treatment.


Because no one knows for sure what causes fibroids, we also don’t know what causes them to grow or shrink. We do know that fibroids need the female hormones – estrogen and progesterone – in order to grow. They grow rapidly during pregnancy, when hormone levels are high. They shrink when anti-hormone medication is used. They also stop growing or shrink once a woman reaches menopause. Medical studies are underway to help shed light on these questions.

How do I know that I have Fibroids?

  • Your doctor may find that you have fibroids when you see her or him for a regular pelvic exam to check your uterus, ovaries, and vagina. The doctor can feel the fibroid with her or his fingers during an ordinary pelvic exam, as a (usually painless) lump or mass on the uterus.
  • Your doctor can do imaging tests to confirm that you have fibroids. These are tests that create a “picture” of the inside of your body without surgery.

These tests might include:

  • Ultrasound – uses sound waves to produce the picture. The ultrasound probe can be placed on the abdomen or it can be placed inside the vagina to make the picture.
  • Magnetic Resonance Imaging (MRI) – uses magnets and radio waves to produce the picture .
  • X-rays – uses a form of radiation to see into the body and produce the picture.
  • Cat Scan (CT) – takes many X-ray pictures of the body from different angles for a more complete image.
  • Hysterosalpingogram (HSG) or sonohysterogram – An HSG involves injecting x-ray dye into the uterus and taking x-ray pictures. A sonohysterogram involves injecting water into the uterus and making ultrasound pictures.

What questions should I ask my doctor if I have fibroids?

  • How many fibroids do I have?
  • What size is my fibroid(s)?
  • Where is my fibroid(s) located?
  • How rapidly have they grown (if they were known about already)?
  • How will I know if the fibroid(s) is growing larger?
  • What problems can the fibroid(s) cause?
  • What tests or imaging studies are best for keeping track of the growth of my fibroids?
  • What are my treatment options if my fibroid(s) becomes a problem?
  • What are your views on treating fibroids with a hysterectomy versus other types of treatments?

A second opinion is always a good idea if your doctor has not answered your questions completely or does not seem to be meeting your needs.

Fibroid Facts

  • Only one type of fibroid (the submucosal type that bulges into the uterine cavity) has been found to interfere with a woman’s ability to become pregnant. This can be treated effectively with minimally invasive surgery on an outpatient basis.
  • The vast majority of women who are pregnant and have fibroids go on to have full-term, healthy babies.
  • Unless a fibroid is growing in a location that blocks the birth canal, pregnant women with fibroids do not need to have a cesarean section.
  • The kind of cancer that is sometimes mistaken for a fibroid, called leiomyosarcoma, is rare. It has been found in only one out of every 1,000 women admitted to the hospital for fibroid surgery.
  • Most women with fibroids require no treatment at all; however, the growth of fibroids should be monitored by a gynecological exam every 3-6 months. If fibroids become very large and bothersome, or if they cause medical problems, a woman may choose among several treatment options.
  • Major abdominal surgery, either to remove fibroids (abdominal myomectomy) or to remove the entire uterus (hysterectomy), is no longer necessary in the majority of cases.
LEARN MORE Links to related topics
BBC Health: Uterine polyps
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