Uterine fibroids risk factors: who is more likely to get them

What uterine fibroids are

Uterine fibroids, also called leiomyomas, are growths made of smooth muscle cells, fibroblasts and other material that grow in or on the wall of the uterus (womb). They are the most common non-cancerous tumors in women of childbearing age (NICHD). A fibroid may grow alone or in clusters, and one uterus often has many fibroids of different sizes. Fibroids can grow, shrink or stay the same size over time (NICHD).

Health care providers group fibroids by where they grow: submucosal fibroids grow just under the uterine lining and into the cavity of the uterus, intramural fibroids grow within the muscle of the uterus, and subserosal fibroids grow on the outside of the uterus. Fibroids that grow on a stalk are called pedunculated fibroids (NICHD).

You may have fibroids and not know it, because they often cause no symptoms (MedlinePlus). There is no score or calculator for fibroid risk on this page; the lists below are the factors NICHD and MedlinePlus name.

Who is more likely to get uterine fibroids

Fibroids usually grow in women of childbearing age, and research suggests they may shrink after menopause (NICHD). NICHD lists these factors that may affect a woman's risk of fibroids (NICHD):

• Age: older women are at higher risk than younger women.
• African American race. For African American women, fibroids typically develop at a younger age, grow larger and cause more severe symptoms. Research also shows fibroids are more likely to shrink after menopause in white women than in Black women.
• Obesity.
• Family history of uterine fibroids.
• High blood pressure.
• No history of pregnancy.
• Vitamin D deficiency.
• Food additive consumption and use of soybean milk.

MedlinePlus gives a similar list: older age; being Black or African American, with fibroids often at a younger age, larger and with worse symptoms; a mother or sister who had fibroids; periods that started before age 10; never having been pregnant; and conditions such as obesity or vitamin D deficiency (MedlinePlus). See also high blood pressure risk factors.

What may lower the risk

NICHD names two factors that may lower the risk of fibroids (NICHD):

• Pregnancy: the risk goes down as the number of pregnancies goes up.
• Long-term use of birth control pills or shots (oral or injectable contraceptives).

MedlinePlus says the same: your risk lowers with each pregnancy and with long-term use of birth control pills or shots (MedlinePlus).

What causes uterine fibroids

No one knows exactly what causes fibroids. NICHD says evidence suggests several factors may play a role in their growth, and that fibroids are likely caused by many factors acting together (NICHD):

• genetics, such as changes in the MED12, HMGA2, COL4A5/COL4A6 or FH genes;
• the hormones estrogen and progesterone;
• growth hormones;
• micronutrients such as iron; for example, a lack of vitamin D may be linked with fibroids;
• major stresses.

MedlinePlus adds that estrogen and progesterone, the hormones that thicken the lining of the uterus each menstrual cycle, seem to help fibroids grow (MedlinePlus).

Symptoms

Many women have no symptoms. When fibroids do cause symptoms, NICHD lists (NICHD):

• heavy bleeding or painful periods;
• anemia (not having enough red blood cells);
• bleeding between periods;
• a feeling of fullness in the lower belly, sometimes called pelvic pressure;
• needing to urinate often, caused by a fibroid pressing on the bladder;
• pain during sex;
• lower back pain;
• reproductive problems such as infertility, multiple miscarriages and early labor during pregnancy;
• obstetrical problems such as a higher chance of needing a cesarean section.

MedlinePlus says the symptoms depend on where the fibroids are, how big they are and how many there are. Many women with fibroids can get pregnant with no problems, but some fibroids could cause infertility, pregnancy loss, or problems with fetal development or delivery (MedlinePlus). See miscarriage risk factors.

How fibroids are found

Unless she has symptoms, a woman is unlikely to know she has fibroids, though a provider may find them during a routine gynecological exam, when the uterus may feel larger than normal or irregular in shape. The size of fibroids does not seem to match how severe the symptoms are, so even small fibroids may cause heavy periods (NICHD). Imaging tests used to diagnose fibroids include ultrasound, saline infusion sonography, MRI, X-rays and CT scans (NICHD).

Treatment

If you have fibroids but no symptoms or problems, you may not need treatment; your provider can keep checking them at routine exams (NICHD). Treatments include medicines, hysterectomy (removal of the uterus) and other methods. Before recommending one, a provider considers your age, your general health, how severe your symptoms are, where the fibroids are, their type and size, and whether you are pregnant or want to get pregnant in the future (NICHD). NICHD notes that hysterectomy is currently the only cure, although fibroids can be treated in other ways (NICHD). Fibroids often shrink during and after menopause (NICHD).

Common questions

Who is most likely to get uterine fibroids?

NICHD says fibroid risk is higher among women who are older, are African American, have obesity or have a family history of fibroids (NICHD). High blood pressure, never having been pregnant and vitamin D deficiency are also on its list (NICHD).

Are uterine fibroids cancer?

No. Fibroids are noncancerous (benign) tumors (MedlinePlus). For cancer of the uterus, see uterine cancer risk factors.

How are fibroids different from endometriosis?

Fibroids are growths in or on the wall of the uterus (NICHD). In endometriosis, tissue similar to the lining of the uterus grows in other places in the body (NICHD). Both can cause painful periods and problems getting pregnant (NICHD) (NICHD), so talk with your provider about any symptoms.