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. Some key points about fibroids. 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. 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 to shrink, such as 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. Types of FibroidThere are four types of fibroid. The classification of a fibroid depends on its location in the womb.- 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.