Causes of Fibroids

Uterine fibroids are a common problem, affecting about 2/3 of all women over 30. Referred to as fibroid tumors or simply fibroids, they are growths of tissue that develop on or within the walls of the uterus.

Uterine fibroids are typically benign, or non-cancerous, and range from tiny growths that are too small to be seen by the naked eye to large ones that can measure as much as eight inches in diameter.

Although doctors know how fibroids occur, they do not know exactly why, since the direct cause of fibroid tumor development has yet to be conclusively determined.

Fibroid Basics

Fibroids, which may be called leiomyoma or myoma by medical professionals, are made up of smooth muscle cells from the uterus and fibrous connective tissues.

They are classified in three separate groups based upon where they develop. Submucosal fibroids are tumors that grow into the uterine cavity, while subserosal fibroids grow on the outer wall of the uterus, and tumors that develop within the walls of the uterus are called intramural fibroids.

A woman may have a single fibroid or many. Multiple fibroids or one very large tumor can cause the uterus to become distorted and enlarged, sometimes to the point that the abdomen becomes distended, giving a woman the appearance of pregnancy.

Cause of Fibroid Tumor Development

Uterine fibroids occur when a single uterine muscle cell spontaneously begins to reproduce itself over and over again until it creates a firm mass of tissue.

While the cause of fibroid development has not been conclusively identified, research has determined that many fibroid tumors have gene alterations that are not present in normal uterine muscle cells. Scientists speculate that those alterations may be the cause of fibroid development, triggering the abnormal cell replication that is at the root of the process.

While the cause of fibroid tumors is not clear, a number of factors may increase a woman’s risk of developing them. Women most likely to be affected by fibroids include those who have never been pregnant, individuals with a family history of fibroids, and women of African-American heritage.

Some research has suggested that obesity may increase risk, while other studies have show no association between body weight and fibroids.

Cause of Fibroid Growth

While they have not been identified as a direct cause of fibroid development or growth, estrogen and progesterone seem to be related to fibroid growth.

Fibroids tend to develop and grow during a woman’s childbearing years, when the body produces these hormones at peak levels. Once a woman enters menopause, hormone production is greatly reduced and fibroids typically stop growing and may even shrink.

Since fibroids are sensitive to estrogen and progesterone, it would seem logical to assume that birth control pills might be a cause of fibroid growth. However, that is not the case.

Rather than being a cause of fibroid growth, oral contraceptives have been shown to lower risk of fibroid development in women and slow tumor growth in women already affected by fibroids.

Fibroids and Cancer Risk

The vast majority of fibroid tumors are non-cancerous and will remain that way. In extremely rare cases, fibroids can lead to a type of cancer called leiomyosarcoma. This occurs in approximately one of every 1,000 women who develop uterine fibroids, most often after the age of 50.

Since little is known about the cause of fibroid tumors, guidelines to help women reduce risk cannot be developed. However, the identification of high-risk groups can put those women and their doctors on alert, resulting in earlier diagnosis and treatment.

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