Causes
Uterine fibroids are common. As many as one in five women may have fibroids during their childbearing years. Half of all women have fibroids by age 50.
Fibroids are rare in women under age 20. They are more common in African Americans than White, Hispanic, or Asian women.
No one knows exactly what causes fibroids. They are thought to be caused by:
- Hormones in the body
- Genes (may run in families)
Fibroids can be so tiny that you need a microscope to see them. They can also grow very large. They may fill the entire uterus and may weigh several pounds or kilograms. Although it is possible for just one fibroid to develop, most often there is more than one.
Fibroids can grow:
- In the muscle wall of the uterus (myometrial)
- Just under the surface of the uterine lining (submucosal)
- Just under the outside lining of the uterus (subserosal)
- On a long stalk on the outside the uterus or inside the uterus (pedunculated)
