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Uterine Fibroids


Uterine fibroids are nodules of smooth muscle cells and fibrous connective tissue that develop within the wall of the uterus (womb). Medically they are called uterine leiomyomata (singular: leiomyoma). Fibroids may grow as a single nodule or in clusters and may range in size from 1 mm to more than 20 cm (8 inches) in diameter. They may grow within the wall of the uterus or they may project into the interior cavity or toward the outer surface of the uterus. In rare cases, they may grow on stalks or peduncles projecting from the surface of the uterus.

 The factors that initiate fibroid growth are not known. The vast majority of fibroids occur in women of reproductive age, and according to some estimates, they are diagnosed in black women two to three times more frequently than in white women. They are seldom seen in young women who have not begun menarche (menstruation) and they usually stabilize or regress in women who have passed menopause.

Fibroids are the most frequently diagnosed tumor of the female pelvis. It is important to know that these are benign tumors. They are not associated with cancer, they virtually never develop into cancer, and they do not increase a woman's risk for uterine cancer.

No one knows how many new cases of uterine fibroids occur within any given length of time nor how many women have fibroids at any time. It has been estimated that up to 20 to 30 percent of women of reproductive age have fibroids, though not all have been diagnosed. More careful studies, however, indicate that the prevalence may be much higher. A study of 100 uteri that had been removed in consecutive hysterectomies yielded the following results: 33 had been diagnosed as having fibroids prior to surgery; routine pathologic examination disclosed that 52 had fibroids. However, a surprising 77 specimens were found with fibroids upon very close examination. The majority of the tumors were less than 1 cm in diameter and were missed during routine pathologic examination. These results indicate that more than three-quarters of women have uterine fibroids.

This is a small study, however, and its results should not be interpreted as applying to the entire female population, but as an indicator that perhaps the prevalence of fibroids is much higher than has been believed.*

Who is at Risk for Uterine Fibroids?

No risk factors have been found for uterine fibroids other than being a female of reproductive age. However, some factors have been described that seem to be protective. In some studies, again of small numbers of women, investigators found that as a group, women who have had two liveborn children have one-half the risk of having uterine fibroids compared to women who have had no liveborn children. It could not be discerned whether having children actually protects a woman from developing fibroids or whether fibroids contributed to the infertility of women who had no children.

Obese women in some studies were at increased risk of having fibroids, but other studies failed to confirm this. A lower risk has been found in both smokers and users of oral contraceptives in some studies, but not in all. However, it is important to note that smoking poses far greater health hazards than do uterine fibroids. Athletic women also seem to have a lower prevalence compared with women who do not engage in any athletic activities.

 In view of the lack of information on fibroids, the National Institute of Child Health and Human Development (NICHD) is conducting research on the scientific bases for better diagnosis and treatment of fibroid tumors. It is hoped that the results of this research will enable the medical community to better predict who is at risk for fibroids, what can be done to prevent their development, and/or how to provide the most effective treatment for them.

Symptoms of Uterine Fibroids

 How do you know if you have uterine fibroids? Probably you do not know. Most fibroids do not cause any symptoms and do not require treatment other than regular observation by a physician. Fibroids may be discovered during routine gynecologic examination or during prenatal care. Some women who have uterine fibroids may experience symptoms such as excessive or painful bleeding during menstruation, bleeding between periods, a feeling of fullness in the lower abdomen, frequent urination resulting from a fibroid that compresses the bladder, pain during sexual intercourse, or low back pain. Although reproductive symptoms such as infertility, recurrent spontaneous abortion, and early onset of labor during pregnancy have been attributed to fibroids to any of these symptoms. In rare cases, a fibroid can compress and block the fallopian tube, preventing fertilization and migration of the ovum (egg); after surgical removal of the fibroid, fertility is generally restored.

Treatment for Fibroids

 Until very recently, a woman with growing uterine fibroids was considered a candidate for hysterectomy (removal of the uterus). However, treatment by hysterectomy in a woman of reproductive age means that she will no longer be able to bear children and hysterectomy may have other effects, both physical and psychological, as well. A woman considering hysterectomy should discuss the pros and cons thoroughly with her physicians.

Although the number of hysterectomies has been declining since 1987, this operation remains the second most frequently performed surgery in the U.S.; only cesarean section is performed more frequently. Fibroids remain the number-one reason for hysterectomy with 150,000 to 175,000 operations carried out each year because of fibroids.

Hysterectomy for uterine fibroids historically has been based on uterine size. Once the uterus reached the size that it would be in the 12th week of pregnancy it was considered time to perform a hysterectomy. The decision was based mainly on the fact that fibroids of such volume could shield the presence of uterine cancer. Without effective diagnostic procedures the medical community considered it safer to remove the uterus than to possibly harbor a growing malignancy. Now, however, improved imaging procedures such as ultrasound and magnetic resonance imaging (MRI) can effectively determine whether or not a rapidly growing tumor is present, reducing the number of hysterectomies performed. Therapy for uterine fibroids should be based on symptoms and not the idea that uterine fibroids will continue to grow until it becomes necessary to perform a hysterectomy.

If a fibroid is particularly troublesome, the surgeon often can remove only the tumor. leaving the uterus intact (leiomyomectomy).

This may leave the wall of the uterus weakened, in which case any pregnancy that occurs later most likely will be delivered by caesarean section. Many women with fibroids have successful outcomes of pregnancy with no undue incidence of miscarriage or other unfavorable outcome.

More and more, physicians are beginning to realize that uterine fibroids may not require any intervention or, at most, limited treatment. For a woman with uterine fibroids that are not symptomatic the best therapy may be watchful waiting. Some women never exhibit any symptoms or have any problems associated with fibroids, in which case no treatment is necessary. For women who experience occasional pelvic pain or discomfort, a mild, over-the counter anti-inflammatory or painkilling drug often will be effective. More bothersome cases may require stronger drugs available by prescription.

The fact that fibroids seemingly are estrogen-dependent has led to attempts to control them by reduction in available estrogen. Hormone-like agents that counter the action of gonadotropin-releasing hormone (GnRH) are being investigated as one such agent. The use of a GnRH agonist lowers blood levels of estrogen and reduces uterine volume by as much as 60 percent.

Of primary concern in the use of such agents is the possibility of increasing blood cholesterol levels and reducing bone density, which may lead to osteoporosis. Although only modest increases in blood cholesterol have been noted in women undergoing this treatment, the therapy itself was of short duration. Unfortunately, the uterus returned to its pre-treatment size within 3 to 6 months after GnRH agonists were stopped.

It would seem from these observations that the use of GnRH agonists is of limited application. But, in fact, defined protocols have been worked out for administration of these agents for use in women who have symptoms, are poor candidates for surgery, and are nearing menopause. Also, for patients needing a hysterectomy, the use of GnRH agonists can reduce uterine size considerably, making abdominal hysterectomy easier or even allowing a vaginal hysterectomy rather than an abdominal one.

Three GnRH agonists are currently available. Two must be given by injection and the third is administered by an inhaler. Side effects that have been found include hot flushes, depression, insomnia, decreased libido, and joint pain. Maximum uterine shrinkage is achieved after 3 months of therapy.

Studies have only just begun on the newest class of antihormonal agents, the antiprogestins, the best known of which is RU 486.* Even though fibroids appear primarily stimulated by estrogens, drugs in this class which oppose the other major female hormone, progesterone, also seem to be effective for treatment of uterine fibroids. Studies using these drugs are still in the early stages.**


*Cramer, DW. Epidemiology of Myomas. Seminars in Reproductive Endocrinology 10:320-324, 1992

* *Supported by San Diego Reproductive Medicine Educational and Research Foundation, and NIH Grant RR-00827

***Murphy, AA et al. Journal of Clinical Endocrinology and Metabolism