Fibroids: Causes, symptoms, and treatments

Uterine fibroids are non-cancerous tumors that grow from the muscle layers of the womb. These benign growths of smooth muscle can vary from the size of a bean to being as large as a melon.

They are also known as leiomyomas and myomas.

Fibroids affect around 30 percent of all women by the age of 35 years, and from 20 to 80 percent by the age of 50 years.

They usually develop between the ages of 16 to 50 years. These are the reproductive years during which estrogen levels are higher.

This MNT Knowledge Center article will look at the types of fibroid, their effects on the body, what causes them, how they are discovered, and what women can do to treat them.

Fast facts on fibroids:

Here are some key points about fibroids. More information is in the main article.

Fibroids are most common during the reproductive years.

It is unclear exactly why they form, but they appear to develop when estrogen levels are higher.

Most people experience no symptoms, but they can include lower backache, constipation, and excessive or painful uterine bleeding leading to anemia.

Complications are rare, but they can be serious.


Fibroids are non-cancerous tumors that appear in the tissues around the womb.

There are four types of fibroid:

Intramural: This is the most common type. An intramural fibroid is embedded in the muscular wall of the womb.

Subserosal fibroids: These extend beyond the wall of the womb and grow within the surrounding outer uterine tissue layer. They can develop into pedunculated fibroids, where the fibroid has a stalk and can become quite large.

Submucosal fibroids: This type can push into the cavity of the womb. It is usually found in the muscle beneath the inner lining of the wall.

Cervical fibroids: Cervical fibroids take root in the neck of the womb, known as the cervix.

The classification of a fibroid depends on its location in the womb.

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Around 1 in 3 women with fibroids will experience symptoms.

These may include:

heavy, painful periods, also known as menorrhagia

anemia from heavy periods

lower backache or leg pain


discomfort in the lower abdomen, especially in the case of large fibroids

frequent urination

pain during intercourse, known as dyspareunia

Other possible symptoms include:

labor problems

pregnancy problems

fertility problems

repeated miscarriages

If fibroids are large, there may also be weight gain and swelling in the lower abdomen.

Once a fibroid develops, it can continue to grow until menopause. As estrogen levels fall after menopause, the fibroid will usually shrink.


It remains unclear exactly what causes fibroids. They may be related to estrogen levels.

During the reproductive years, estrogen and progesterone levels are higher.

When estrogen levels are high, especially during pregnancy, fibroids tend to swell. They are also more likely to develop when a woman is taking birth control pills that contain estrogen.

Low estrogen levels can cause fibroids may shrink, such during and after menopause.

Genetic factors are thought to impact the development of fibroids. Having a close relative with fibroids increases the chance of developing them.

There is also evidence that red meat, alcohol, and caffeine could increase the risk of fibroids, and that an increased intake of fruit and vegetables might reduce it.

Being overweight or obese increases the risk of fibroids.

Childbearing lowers the risk of developing fibroids. The risk reduces each time a woman gives birth.

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