What Are Uterine Fibroids?

A uterine fibroid, known in medicine as a leiomyoma or simply as a myoma, is a noncancerous growth of muscle and connective tissue in the uterus. The size of a fibroid ranges from the head of a pin to a large melon, individual tumors sometimes weighing as much as 20 pounds (9 kilograms). Uterine fibroids are the most common tumor of the female reproductive organs. Some studies estimate that up to 80 percent of women between the ages of 30 and 50 have uterine fibroids, although only 25 percent of women experience symptoms. In the United States, African-American women are especially likely to suffer fibroids, and they tend to have more numerous fibroids causing pain and anemia.

Uterine fibroids can do serious damage to fertility. Fibroids can block the cervix so that sperm cannot reach the uterus. They can block the fallopian tubes so that the egg cannot reach the uterus. They can distort the endometrium so that a fertilized egg cannot attach itself and begin growth. When pregnancy is achieved, small fibroids are enough to increase the risk of miscarriage. Fibroids pressing against the urinary canal elevate the risk of urinary tract infections, and any fibroid can cause pain.

The growth of fibroids is fueled by estrogen. Fibroids often first appear during pregnancy, when a woman’s body produces enormous quantities of estrogen, and disappear during menopause, when estrogen production is greatly decreased. The hormone progesterone also plays a role in the growth of fibroids. These two hormones together keep the fibroid alive and protect it from natural processes that would cause it to shrink and die.

The risk factors for fibroids are high estrogen levels, such as the use of high-estrogen oral contraceptives, use of estrogen replacement therapy, or overweight. Poor circulation does not accelerate the formation of fibroids, but it can make existing fibroids intensely painful. Women who have high blood pressure, especially women who begin taking high blood pressure medication before age 35, are especially likely to suffer painful fibroids. Other risk factors include history of pelvic inflammatory disease or chlamydia, infections caused by a poorly fitted IUD, and regular use of feminine hygiene products containing talcum powder.