Fibroids are composed primarily of muscle cells that grow as a single lump or cluster of lumps within the uterine wall. They affect an estimated 77 percent of American women, most of whom don't even know they have them.

Fibroids range in size from less than one inch in diameter to the size of a grapefruit. They are responsible for more than 200,000 hysterectomies every year nationwide.

Fibroids are classified in three ways, depending on their location:

• Submucosal. These grow just under the uterine lining into the uterine cavity. They can cause bleeding, pain and infertility.
  
• Intramural. This most common type of fibroid grows in between the muscles of the uterine wall. These fibroids usually cause pressure-type symptoms and, less often, heavy menstruation.
  
• Subserosal. These fIbroids grow from the uterine wall to the outside of the uterus. They can push on other organs, such as the bladder, bowel or intestine, causing abdominal bloating, pressure, cramps or pain.

Some fibroids grow on "stalks" sticking out from the uterus or into the uterine cavity. Should the stalks twist, they can cause pain and nausea as the tissue degenerates or fever if they become infected.

Causes. Fibroids are most common among women between ages 30 and 40, among African-American women and women with a family history of fibroids. Being overweight raises your risk slightly, while childbirth and being athletic seem to lower your risk slightly. Some studies suggest that women who use oral contraceptives have a lower risk, too. Estrogen is known to influence fibroid growth, but the exact cause of fibroids is unknown.

Symptoms. Most fibroids produce no symptoms. If fibroids trigger symptoms- generally because of their size, number or location-they can cause longer and heavier menstrual bleeding, pelvic discomfort and pain, pressure on other organs, miscarriages and infertility. Having fibroids also increases your risk of complications during pregnancy.

Diagnosis. Your health care professional may be able to feel fibroids during a pelvic exam. One or more tests or procedures may be used to diagnose fibroids. However, it should be noted that these tests may identify fibroids that haven't triggered any symptoms and may not require treatment. (See "Tests Used to Diagnose Uterine Conditions" below.)

Treatment. Fibroids need treatment only if they cause problems. Because fibroids tend to shrink after menopause, women in their late 40s and early 50s with fibroidrelated symptoms may opt to wait and see if the symptoms go away.

Treatment depends on the size of your fibroids, your symptoms and whether you are planning a pregnancy. The only cure is a hysterectomy, but other less radical treatments may provide symptom relief. These treatments include:

• Myomectomy. This procedure removes just the fibroids, leaving the uterus intact. It's a good option for women who want to maintain their fertility, but the fibroids may eventually recur. A myomectomy can be performed through a long abdominal incision, laparoscopically (through tiny incisions in the abdomen), or hysteroscopically (through the cervix with no incision). The form of surgery depends on the size and location of your fibroids, your medical history and your surgeon's preference.

• Uterine artery embolization. One of the newest, non-surgical methods of treating fibroids, this procedure is still being studied. It works by cutting the blood supply to the arteries that feed the fibroids. Risks include infection or massive bleeding that may require emergency surgery.

• Myolysis. Another experimental procedure still under study, myolysis involves using lasers, electrical current or freezing (cryomyolysis) to destroy fibroids during a laparoscopy. No long-term studies on safety and effectiveness have been conducted on this procedure.

Prevention. There is no known way to prevent fibroids.