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Uterine Fibroids Health Center

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Understanding Uterine Fibroids -- the Basics

What Are Uterine Fibroids?


The uterus is a muscular, hollow, pear-shaped organ in the pelvis. The lower portion narrows into the cervix, which opens to the vagina.

Fibroids are benign (noncancerous) tumors, or growths of the muscle and connective tissue of the uterus. They usually grow slowly and may occur inside the uterus, within the uterine wall, or on the outside surface of the uterus. They occur in 20% to 50% of women of reproductive age. Fibroids are more common in African-American women.

Women with fibroids may have uterine pain and abnormal bleeding -- usually heavy, prolonged periods. Many women with smaller fibroids have no symptoms at all.

During normal reproduction, a fertilized egg implants itself in the wall of the uterus. It is here that the embryo develops and grows into a baby, and where the baby is nourished until birth.

Uterine fibroids may change the shape of the uterus and make it difficult to become pregnant. Fibroids may also lead to miscarriages.

Sometimes, a fibroid attached to the outside of the uterus becomes twisted, or large fibroids outgrow their blood supply, leaving them starved for blood and oxygen. If this happens, you may suddenly feel a sharp pain in your abdomen. This pain can feel crampy in nature, similar to labor pains, because the uterus may be contracting.

Fibroids may cause bladder or bowel pressure, or make sex painful. If they cause periods to become too heavy, they can lead to anemia (low levels of red blood cells in the blood).

Some fibroids enlarge during pregnancy. Complications of having fibroids during pregnancy include:

  • Early labor
  • The baby is not positioned ''head down'' for birth
  • The fetus grows poorly
  • Placenta abruption (the placenta detaches from the uterine wall)
  • Bleeding in the mother after delivery
  • Miscarriage

Fibroids usually shrink after menopause.

Fibroids are thought to develop due to genetic mutations. Their growth is related to hormones; birth control pills, estrogen replacement therapy, and pregnancy may cause fibroids to grow and expand.

WebMD Medical Reference

Reviewed by Trina Pagano, MD on March 14, 2015

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