Fibroids

This page is reference information compiled from the cited sources. It is not medical advice. For any decision about health, diagnosis or care, consult a qualified professional.

What it is

Uterine fibroids are benign smooth muscle tumors of the uterus, which is part of the female reproductive system. They are also known as uterine leiomyomas or fibromyoma. Fibroids grossly appear as round, well-circumscribed, solid nodules that are white or tan and show a whorled appearance on histological section. The size of fibroids varies, from microscopic to lesions of considerable size, with lesions the size of a grapefruit or bigger often felt by the patient through the abdominal wall. Microscopically, the tumor cells resemble normal cells, being elongated and spindle-shaped with a cigar-shaped nucleus, and they form bundles with different directions. There are three benign variants of these cells: bizarre (atypical), cellular, and mitotically active. Fibroids may be single or multiple, and if the uterus contains too many to count, it is referred to as diffuse uterine leiomyomatosis.

Key facts

About 20% to 80% of women develop fibroids by the age of 50, and they are typically found during the middle and later reproductive years. In 2013, it was estimated that 171 million women were affected worldwide. Most women with fibroids have no symptoms, while others may have painful or heavy menstrual bleeding. Fibroids are dependent on estrogen and progesterone to grow and therefore are most relevant during the reproductive years, usually decreasing in size after menopause. The exact cause of uterine fibroids is unclear, but they run in families and appear to be partly determined by hormone levels and partly genetic, with the risk in a daughter being about three times higher than average if the mother has fibroids. Fifty percent of uterine fibroids demonstrate a genetic abnormality, and 80–85% of fibroids have a mutation in the mediator complex subunit 12 (MED12) gene. A 2016 study found black women are more likely than white women to develop uterine fibroids, by an estimated 3–9 times higher rate, with newer data from 2025 suggesting substantial fibroid burden among several Asian populations as well.

When to seek professional help

Professional care is associated with situations where symptoms are present. This includes experiencing painful or heavy menstrual bleeding. It also includes situations where fibroids cause a frequent need to urinate by pushing on the bladder, or cause pain during penetrative sex or lower back pain. Professional evaluation is indicated if there is abdominal pain, anemia, or heavy or increased bleeding. It is also associated with problems during pregnancy, such as miscarriage, bleeding, premature labor, or interference with the position of the fetus. Professional help is relevant if the abdomen grows larger, mimicking the appearance of pregnancy, or if there is rectal pressure. Diagnosis can be performed by pelvic examination or medical imaging when such symptoms or signs are present.

Source: Uterine fibroid (CC BY-SA 4.0 (Wikipedia)), retrieved 2026-09-27.