What are uterine fibroids?

Uterine fibroids (also called leiomyomas) are growths made up of the muscle and connective tissue from the wall of the uterus. These growths are usually not cancerous (benign). Your uterus is an upside down pear-shaped organ in your pelvis. The normal size is the size of your uterus is similar to a lemon. It’s also called the womb and it’s the place where a baby grows and develops during pregnancy.

Fibroids can grows as a single nodule (one growth) or in a cluster. Fibroid clusters can range in size from 1 mm to more than 20 cm (8 inches) in diameter or even larger. For comparison, they can get as large as the size of a watermelon. These growths can develop within the wall of the uterus, inside the main cavity of the organ or even on the outer surface. Fibroids can vary in size, number and location within and on your uterus.

You may experience a variety of symptoms with uterine fibroids and these may not be the same symptoms that another woman with fibroids will experience. Because of how unique fibroids can be, your treatment plan will depend on your individual case.

Are fibroids common?

Fibroids are actually a very common type of growth in your pelvis. Approximately 40 to 80% of women have fibroids. However, many women don’t experience any symptoms from their fibroids, so they don’t realize they have fibroids. This can happen when you have small fibroids — called asymptomatic because they don’t cause you to feel anything unusual.

Who is at risk for uterine fibroids?

There are several risk factors that can play a role in your chances of developing fibroids. These can include:

  • Obesity and a higher body weight (a person is considered obese if they’re more than 20% over the healthy body weight).
  • Family history of fibroids.
  • Not having children.
  • Early onset of menstruation (getting your period at a young age).
  • Late age for menopause.

Where do fibroids grow?

There are several places both inside and outside of your uterus where fibroids can grow. The location and size of your fibroids is important for your treatment. Where your fibroids are growing, how big they are and how many of them you have will determine which type of treatment will work best for you or if treatment is even necessary.

There are different names given for the places your fibroids are located in and on the uterus. These names describe not only where the fibroid is, but how it’s attached. Specific locations where you can have uterine fibroids include:

  • Submucosal fibroids: In this case, the fibroids are growing inside the uterine space (cavity) where a baby grows during pregnancy. Think of the growths extending down into the empty space in the middle of the uterus.
  • Intramural fibroids: These fibroids are embedded into the wall of the uterus itself. Picture the sides of the uterus like walls of a house. The fibroids are growing inside this muscular wall.
  • Subserosal fibroids: Located on the outside of the uterus this time, these fibroids are connected closely to the outside wall of the uterus.
  • Pedunculated fibroids: The least common type, these fibroids are also located on the outside of the uterus. However, pedunculated fibroids are connected to the uterus with a thin stem. They’re often described as mushroom-like because they have a stalk and then a much wider top.

What do fibroids look like?

Fibroids are typically rounded growths that can look like nodules of smooth muscle tissue. In some cases, they can be attached with a thin stem, giving them a mushroom-like appearance.

Are fibroids cancer?

It’s extremely rare for a fibroid to go through changes that transform it into a cancerous or a malignant tumor. In fact, one out of 350 women with fibroids will develop malignancy. There’s no test that’s 100% predictive in detecting rare fibroid-related cancers. However, people who have rapid growth of uterine fibroids, or fibroids that grow during menopause, should be evaluated immediately.

What causes uterine fibroids?

The causes of fibroids are not known. Most fibroids happen in women of reproductive age. They typically aren’t seen in young women who haven’t had their first period yet.

What are the symptoms of uterine fibroids?

Most fibroids do not cause any symptoms and don’t require treatment other than regular observation by your healthcare provider. These are typically small fibroids. When you don’t experience symptoms, it’s called an asymptomatic fibroid. Larger fibroids can cause you to experience a variety of symptoms, including:

The symptoms of uterine fibroids usually stabilize or go away after you’ve gone through menopause because hormone levels decline within your body.

What does uterine fibroid pain feel like?

There are a variety of feelings you might experience if you have fibroids. If you have small fibroids, you may feel nothing at all and not even notice they’re there. For larger fibroids, however, you can experience discomforts and even pains related to the condition. Fibroids can cause you to feel back pain, severe menstrual cramps, sharp stabbing pains in your abdomen and even pain during sex.

Can fibroids change over time?

Fibroids can actually shrink or grow over time. They can change size suddenly or steadily over a long period of time. This can happen for a variety of reasons, but in most cases this change in fibroid size is linked to the amount of hormones in your body. When you have high levels of hormones in your body, fibroids can get bigger. This can happen at several specific times in your life, like during pregnancy. Your body releases high levels of hormones during pregnancy to support the growth of your baby. This surge of hormones also causes the fibroid to grow. If you know you have fibroids before a pregnancy, talk to your healthcare provider. You may need to be monitored to see how the fibroid grows throughout the pregnancy.

Fibroids can also shrink when your hormone levels drop. This is common after menopause. Once a woman has passed through menopause, the amount of hormones in her body is much lower. This can cause the fibroids to shrink in size. Often, your symptoms can also get better after menopause.

Can fibroids cause anemia?

Anemia is a condition that happens when your body doesn’t have enough healthy red blood cells to carry oxygen to your organs. It can make you feel tired and weak. Some women may develop intense cravings for ice, starch, or dirt. This is called pica and is associated with anemia. Anemia can happen to women who have frequent or extremely heavy periods. Fibroids can cause your periods to be very heavy or for you to even bleed between periods. Some treatments like oral iron pills — or if you're significantly anemic, an iron infusion (by IV) — can improve your anemia. Talk to your healthcare provider if you are experiencing symptoms of anemia while you have fibroids.

Last reviewed by a Cleveland Clinic medical professional on 08/24/2020.

References

  • US Department of Health and Human Services, Office on Women’s Health. Uterine fibroids. Accessed 8/24/2020.
  • The American College of Obstetricians and Gynecologists. Uterine Fibroids. Accessed 8/24/2020.
  • Merck Manual Professional Version. Uterine Fibroids. Accessed 8/24/2020.
  • US Department of Health and Human Services, Eunice Kennedy Shriver National Institute of Child Health and Human Development. Uterine Fibroids. Accessed 8/24/2020.

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