Fibroids are tumors that sometimes grow in the wall of the uterus (womb). They are the result of abnormal cell development, but are almost always benign. Fibroid tumors vary in size and number, may grow as a single nodule or in clusters, and their size can range from very small to large masses that can distort the uterus and nearby organs.

Uterine fibroids tend to grow slowly over time during the reproductive years, and are most common in women in their thirties and forties. After menopause, the tumors usually shrink in size.

There are three main types of fibroids: Intramural (which develop in the muscular layers of the uterine wall and are the most common), subserosal (which grow from the outer wall of the uterus), and submucosal (which grow into the uterine cavity and may cause heavy periods, recurrent miscarriages or infertility). If you have fibroids, you may have one or many, and you may have fibroid at one or multiple sites.

What causes fibroids?

The exact causes of fibroids are not understood. However, research indicates that the female hormone oestrogen is a contributing factor in development. This may explain why fibroids grow during pregnancy when oestrogen levels are high, and shrink or disappear altogether after menopause when oestrogen levels drop.