Fibroids are non-cancerous growths in the womb (uterus). They are common and usually cause no symptoms. However, they can sometimes cause heavy periods, tummy (abdominal) swelling and urinary problems. Treatment is available if symptoms occur.

What are fibroids

A fibroid is a benign (non-cancerous) growth of the womb (uterus). They are also called uterine myomas, fibromyomas or leiomyomas. Their size can vary. Some are the same size as a pea and some can be as big as a melon. Fibroids can increase in size, decrease in size or even go away with time. They can occur anywhere in the womb and are named according to where they grow: Intramural fibroids grow within the muscle tissue of the womb. This is the most common place for fibroids to form. Subserous fibroids grow from the outside wall of the womb into the pelvis. Submucous fibroids grow from the inner wall into the middle of the womb. Pedunculated fibroids grow from the outside wall of the womb and are attached to it by a narrow stalk.

How common are fibroids

They are common. At least 1 in 4 women develop one or more fibroids in their lifetime. They usually develop in women aged 30-50 and can sometimes run in families. It is common to have several of various sizes, although some women just have one. Fibroids are more common in women from Afro-Caribbean origin. They also tend to be larger, occur at an earlier age and are more likely to cause symptoms in Afro-Caribbean women.

What causes fibroids

A fibroid is like an overgrowth of smooth muscle cells. (The womb (uterus) is mainly made of smooth muscle.) It is not clear why they develop. Fibroids are sensitive to oestrogen, the hormone that is made in the ovary. Fibroids tend to swell when levels of oestrogen are high - for example, during pregnancy. They also shrink when oestrogen levels are low - after the menopause. This shrinkage of the fibroids after the menopause may be delayed if you take hormone replacement therapy (HRT).