Fibroids are benign (non-cancerous) growths of the muscle of the uterus (womb). They are sometimes called myomas, fibromyomas or leiomyomas, but most people call them fibroids. Around 20% of women get fibroids.
Fibroids grow very slowly and tend not to cause any problems or symptoms in younger women. They can cause symptoms as they grow bigger, but even so, at least half of all fibroids cause no problems at all.
Fibroids can be tiny or very large and a woman may have one or many. Their growth is stimulated by the hormone oestrogen, which is released from the ovaries during the reproductive years. Fibroids tend to become smaller after the menopause when oestrogen levels fall.
There are different types of fibroids, named according to where they are found. The problems that they may cause depend on their location:
- Intramural fibroids are found within the muscular wall of the uterus.
- Subserosal fibroids grow outwards from the outside wall of the uterus. They can become very large,
- Submucosal fibroids grow from the inner wall of the uterus and can take up space inside the uterus. These account for only 5% of all fibroids.
Fibroids are not the same as polyps. Polyps grow from the lining of the uterus (the endometrium) rather than from the underlying muscle as is the case with fibroids.