What is Fibroids?

Fibroids

What are fibroids?

Fibroids are lumps that grow in your womb. They're not cancer and they don't usually cause any problems. We're not sure why women get fibroids, but they are common.

If you have heavy periods, painful periods or a feeling of fullness or discomfort in your

pelvis
Your pelvis is the area between your hips.

pelvis, you may want to get checked by your doctor to see if you have fibroids.

If you have fibroids and they're causing problems, there are many treatments that can help. The best treatments involve surgery. But if you're nearing

menopause
When a woman stops having periods, it is called menopause. This usually happens around the age of 50.

menopause (when your periods stop), you may choose to wait. Fibroids often get better on their own around this time.

Key points for women with fibroids

Fibroids are very common and are usually harmless.
As many as 3 in 4 women may have fibroids. But less than half of these women have any symptoms.
The most common symptoms are heavy periods, painful periods or a feeling of fullness or discomfort in your

pelvis
Your pelvis is the area between your hips.

pelvis.
Fibroids are easy to diagnose. Doctors usually diagnose them with an

ultrasound
Ultrasound is a tool doctors use to create images of the inside of your body. The ultrasound machine sends out high-frequency sound waves, which are directed at an area of your body through a device such as a probe. The waves reflect off parts of your body to create a picture. Ultrasound is often used to see a developing baby inside a woman's womb.

ultrasound scan.
Fibroids don't usually keep you from getting pregnant or make your pregnancy difficult.

Your womb

To understand what happens if you have fibroids, it helps to know more about your womb.

You can have a simple test to find out whether you have fibroids.

Your womb has three layers.

The inner layer of the womb is the lining (or endometrium).
In the middle is a thick layer of muscle called the myometrium.
The outside has a thin cover called the serosal layer.

Every month, the lining of your womb grows thicker to get ready for pregnancy. This is controlled by two

hormones
Hormones are chemicals that are made in certain parts of the body. They travel through the bloodstream and have an effect on other parts of the body. For example, the female sex hormone estrogen is made in a woman's ovaries. Estrogen has many different effects on a woman's body. It makes the breasts grow at puberty and helps control periods. It is also needed to get pregnant.

hormones called estrogen and progesterone.

If you don't get pregnant, the lining of your womb falls away and out of your vagina. This is your monthly period.

The changes in your womb lining are part of your menstrual cycle. This is the monthly set of events that causes an egg to come out of your ovaries. It also causes your period to happen if you aren't pregnant.

To learn more, see What happens every month.

What happens if you have fibroids?

Fibroids are lumps that grow in your womb. They are made of the same cells that form certain kinds of muscles. Doctors sometimes call them tumors, but fibroids aren't cancer and don't turn into cancer.

You can have just one fibroid or many. The average number is six.

Source:
Cramer SF, Patel A.
The frequency of uterine leiomyomas.
American Journal of Clinical Pathology. 1990; 94: 435-438.

¹ They can be tiny, about the size of a pinhead. Or they can grow to be large, sometimes as big as a balloon.

Source:
National Institute of Child Health and Human Development.
Uterine fibroids.
Available at http://www.nichd.nih.gov/publications/pubs/fibroids.cfm (accessed on 27 June 2008).

² The average size is two-thirds of an inch.

Source:
Cramer SF, Patel A.
The frequency of uterine leiomyomas.
American Journal of Clinical Pathology. 1990; 94: 435-438.

¹ They usually grow slowly.

They can grow:

Source:
Stewart EA.
Uterine fibroids.
Lancet. 2001; 357: 293-298.

Fibroids can grow in different parts of your womb.

On the inside of your womb, just under the lining
In the layer of muscle
On the outside of your womb, just under the cover.

But very often fibroids are what doctors call "mixed." This means they grow into two different parts of your womb.

What causes fibroids?

Doctors don't know what causes fibroids. The hormone estrogen seems to make them grow.

Source:
Rein MS, Barbieri RL, Friedman AJ.
Progesterone: a critical role in the pathogenesis of uterine myomas.
American Journal of Obstetrics and Gynecology. 1995; 172:14-18.

⁴

When you go through menopause, your body stops making so much estrogen. So your fibroids start to shrink. If you have a treatment called

hormone replacement therapy
Hormone replacement therapy (also called HRT) is given to women after menopause to replace the estrogen (the main female hormone) that is no longer made by their ovaries. It can be given either as estrogen alone or as a combination of estrogen and progestin (another female hormone). It is useful to treat menopausal symptoms such as hot flushes, and to prevent brittle bone disease (osteoporosis). But there are concerns that it may increase the risk of breast cancer, heart attacks and strokes.

hormone replacement therapy (HRT for short), your fibroids may start growing again.

Source:
Sener AB, Seckin NC, Ozmen S, et al.
The effects of hormone replacement therapy on uterine fibroids in postmenopausal women.
Fertility and Sterility. 1996; 65: 354-357.

⁵

Why me?

We don't know why some women get fibroids and others don't. But we do know that some things make women more likely to get fibroids. These are called risk factors.

Two things that give you a higher chance of having fibroids are having no children and being

obesity
If your body stores more energy than you need for daily functioning, this can make you overweight. The excess energy is stored in your fat cells. If your weight goes above a certain level, doctors call this obesity. Obesity is considered a medical condition. The excess weight can be a strain on your bones and joints. And if you are obese, you're more likely to get other diseases. Doctors have developed a scale for telling how much excess weight you have. This measure, called the body mass index (BMI), depends on your height.

obese. If you are obese it means you are very overweight.

African-American women are at higher risk of getting fibroids.

To read more, see Risk factors for fibroids.

Sources for the information on this page:

Cramer SF, Patel A.The frequency of uterine leiomyomas.American Journal of Clinical Pathology. 1990; 94: 435-438.

National Institute of Child Health and Human Development.Uterine fibroids.Available at http://www.nichd.nih.gov/publications/pubs/fibroids.cfm (accessed on 27 June 2008).

Stewart EA.Uterine fibroids.Lancet. 2001; 357: 293-298.

Rein MS, Barbieri RL, Friedman AJ.Progesterone: a critical role in the pathogenesis of uterine myomas.American Journal of Obstetrics and Gynecology. 1995; 172:14-18.

Sener AB, Seckin NC, Ozmen S, et al.The effects of hormone replacement therapy on uterine fibroids in postmenopausal women.Fertility and Sterility. 1996; 65: 354-357.

This information was last updated on May 12, 2009

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment.
© BMJ Publishing Group Limited 2009. All rights reserved.

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