Fibroids, also called leiomyomas or fibromas, are benign (non-cancerous) uterine tumors. They are made up of normal uterine muscle cells, growing in abnormal, disorganized clumps. A good comparison is moles on the skin–also normal tissue in abnormal clumps. Fibroids can grow within the uterine wall ("mural" type), on the outside of the uterus ("serosal" type), or inside the uterine cavity ("submucosal" type). They can even grow on a mushroom–like stalk ("Pedunculated" type).

An individual woman may have single or multiple fibroids. In fact, there can be a mixture of different types present in any given patient. They may range in size from a few millimeters (the size of a pea) to 40 centimeters (the size of a full-term baby).

Fibroids are responsive to hormonal stimulation, especially that of estrogen, and may grow steadily during the fertile period of a woman's life. They frequently begin to shrink after menopause.

Fibroids are vascular tumors. That means that they have a rich supply of blood vessels, most often coming from the uterine artery. Pedunculated fibroids can sometimes lose this blood supply spontaneously, by twisting around on the stalk. When this happens, the fibroid will usually begin to shrink. The uterine fibroid embolization (UFE) procedure duplicates this naturally-occurring process.

How common are they?

Fibroids are present in 25-30% of women, and are slightly more common among African-Americans. Only about half of the women with fibroids develop symptoms, but these patients represent one-third of the 600,000 patients who have hysterectomies in the United States every year. In other words, fibroids result in 200,000 hysterectomies every year.

What symptoms do they cause?

Symptoms are present in about half of the women with fibroids. The most common symptoms are pelvic pain, pain during sex, excessive vaginal bleeding, and a feeling of abdominal or pelvic fullness. In addition, the weight of a fibroid can compress the colon and urinary bladder, causing constipation or frequent urination. A very large fibroid can compress the veins that drain blood from the legs, causing leg swelling. In severe cases, the flow of urine from the kidneys can be blocked, injuring the kidneys.

Not every woman with the symptoms listed above has fibroids. There can be other causes for vaginal bleeding, pelvic pain, and pain during sex. Some of these conditions can be serious, and require treatment. Before assuming that fibroids are the culprit, each woman must be completely evaluated by a doctor with experience and training in women's health. For a list of gynecologists in your area, click here.

Do they cause infertility?

The answer to this question is a bit complicated. Pregnancy is defined as the implantation (attachment) of a fertilized egg to the uterine wall. Fibroids do not prevent fertilization. They can, however, prevent the fertilized egg from attaching to the uterine wall, or prevent the uterine cavity from expanding normally to accommodate the growing fetus. In other words, fibroids do not prevent pregnancy, but they can cause miscarriages.

Do they have to be treated?

This is an issue of personal comfort, and personal preference. It is important to remember that fibroids are benign (non–cancerous), and only cause symptoms in about half of the women who have them. Fibroids that are asymptomatic rarely require treatment. Even if there are mild symptoms, a woman may not be terribly bothered, and may not want treatment. However, when these symptoms begin to have a negative impact on the woman's quality of life, then the fibroids should be treated. They should also be treated if they are compressing the ureters–tubes that connect the kidney to the bladder– and causing blockage of urine (this is easily detected with an ultrasound study).