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Uterine Fibroids
(Benign Tumors Of The Uterus)

Medical Author:

Melissa Conrad Stöppler, MD

Melissa Conrad Stöppler, MD

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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Medical Editor:

William C. Shiel Jr., MD, FACP, FACR

William C. Shiel Jr., MD, FACP, FACR

Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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What are uterine fibroids?

Uterine fibroids are benign tumors that originate in the uterus (womb). Although they are composed of the same smooth muscle fibers as the uterine wall (myometrium), they are many times denser than normal myometrium. Uterine fibroids are usually round or semi-round in shape.

Uterine fibroids are often described based upon their location within the uterus. Subserosal fibroids are located beneath the serosa (the lining membrane on the outside of the organ). These often appear localized on the outside surface of the uterus or may be attached to the outside surface by a pedicle. Submucosal (submucous) fibroids are located inside the uterine cavity beneath the lining of the uterus. Intramural fibroids are located within the muscular wall of the uterus.

What causes uterine fibroids and how common are they?

We do not know exactly why women develop these tumors. Genetic abnormalities, alterations in growth factor (proteins formed in the body that direct the rate and extent of cell proliferation) expression, abnormalities in the vascular (blood vessel) system, and tissue response to injury have all been suggested to play a role in the development of fibroids.

Family history is a key factor, since there is often a history of fibroids developing in women of the same family. Race also appears to play a role. Women of African descent are two to three times more likely to develop fibroids than women of other races. Women of African ancestry also develop fibroids at a younger age and may have symptoms from fibroids in their 20s, in contrast to Caucasian women with fibroids, in whom symptoms typically occur during the 30s and 40s. Pregnancy and taking oral contraceptives both decrease the likelihood that fibroids will develop. Fibroids have not been observed in girls who have not reached puberty, but adolescent girls may rarely develop fibroids. Other factors that researchers have associated with an increased risk of developing fibroids include having the first menstrual period (menarche) prior to age 10, consumption of alcohol (particularly beer), uterine infections, and elevated blood pressure (hypertension).

Estrogen tends to stimulate the growth of fibroids in many cases. During the first trimester of pregnancy, up to 30% of fibroids will enlarge and then shrink after the birth. In general, fibroids tend to shrink after menopause, but postmenopausal hormone therapy may cause symptoms to persist.

Overall, these tumors are fairly common and occur in up to 50% of all women. Most of the time, uterine fibroids do not cause symptoms or problems, and a woman with a fibroid is usually unaware of its presence.