Overview of Uterine Fibroids

Uterine fibroids are abnormal growths, or tumors, that develop in the tissue of the uterus. They also are called uterine fibromata (singular is fibroma) and uterine leiomyomata. Uterine fibroids are common and occur in about 40 percent of women by the age of 40.

The uterus (womb) is the female reproductive organ in which a fertilized egg (ovum) implants and develops during pregnancy. It is located in the pelvis, behind the bladder and in front of the rectum in women. The uterus has thick, muscular walls and consists of a broad, upper part (called the corpus), a constricted middle part (called the isthmus), and a narrow, bottom part (called the cervix).

Uterine fibroids are made up of fibrous connective tissue. They are the most common type of growth in women of childbearing age and usually are slow-growing, irregularly-shaped, and benign (i.e., non-cancerous). Uterine fibroids can vary considerably in size. They may be very small, or larger than a grapefruit, and can occur as a single growth, or as a cluster of growths.

Fibromata can develop in different types of uterine tissue. The most common type develops within the muscular wall of the uterus (e.g., interstitial fibroma). Other types can develop in the uterine lining, on the outside of the uterus, or can grow into the uterine cavity. In addition to uterine tissue, fibroids also can develop in other tissues and organs, such as breast tissue and bone.

Incidence and Prevalence of Uterine Fibroids

Uterine fibroids are common. According to the U.S. Department of Health & Human Services, the condition affects approximately 70–80 percent of women over the age of 50. African American women often develop uterine fibroids at a younger age than women of other races.

Uterine Fibroids Causes and Risk Factors

Uterine fibroids are abnormal growths (tumors) that develop in uterine tissue (i.e., tissue of the uterus). The cause for uterine fibroids is unknown. A combination of genetic (heredity), environmental, and hormonal factors (e.g., estrogen levels) may contribute to the condition.

Age is a risk factor for uterine fibroids. The condition is present in about 40 percent of women by the age of 40 and in 70–80 percent of women over age 50. Women who are of childbearing age (i.e., between puberty and menopause) are at increased risk for developing fibroids of the uterus.

African American women have a higher risk for developing uterine fibroids than women of other races. They also are at increased risk for developing the condition at a younger age. Obesity/overweight increases the risk for fibroids of the uterus.

Women who have given birth may have a lower risk than women who have not had a child. Oral contraceptives (birth control pills) also may reduce the risk.

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 12 Nov 2007

Last Modified: 13 Oct 2015