In fact, it's one of the most common medical conditions affecting women. Fortunately, fibroids are almost always non-cancerous. It's not known what causes fibroids to grow, but they appear to be linked to estrogen production. They usually develop from a single cell that begins to grow rapidly. The fibroids can be so small that they can't be seen without a microscope or can grow as large as 20 inches.
Some women develop a single fibroid, while others develop numerous fibroids.
Since the cause is not known, it's unclear what factors put women at greater risk for developing fibroids. What is known is that most fibroids develop during a woman's reproductive years. They rarely occur before a girl begins menstruation and tend to stabilize or shrink in women past menopause. African American women are two to three times more likely to be diagnosed with fibroids. Most fibroids cause no symptoms.