Uterine fibroids are the most common tumors of the female genital tract. Fibroids are noncancerous (benign) growths that develop in the muscular wall of the uterus. The exact causes for fibroid development are unclear, but researchers have linked them to both a genetic predisposition and to hormone stimulation. This would explain why certain ethnic groups or racial groups are more likely to develop fibroids and also why there tends to be genetic predisposition in some families.

Fibroids range greatly in size from very tiny to the size of a cantaloupe or larger. In some cases, they can cause the uterus to grow in the size of a five-month pregnancy or more. Fibroids may be located in various parts of the uterus. In most cases, there is more than one fibroid in the uterus. There are three primary types of uterine fibroids.

Subserosal fibroids, which develop under the outside covering of the uterus and expand outward through the wall, giving the uterus a knobby appearance. They typically do not affect a woman's menstrual flow, but can cause pelvic pain, back pain and generalized pressure. The subserosal fibroid can develop a stalk or stem-like base, making it difficult to distinguish from an ovarian mass. These are called pedunculated. The correct diagnosis can be made with either an ultrasound or magnetic resonance (MR) exam.

Intramural fibroids, which develop within the lining of the uterus and expand inward, increasing the size of the uterus, and making it feel larger than normal in a gynecologic internal exam. These are the most common fibroids. Intramural fibroids can result in heavier menstrual bleeding and pelvic pain, back pain or the generalized pressure that many women experience.

Submucosal fibroids, which are just under the lining of the uterus. These are the least common fibroids, but they tend to cause the most problems. Even a very small submucosal fibroid can cause heavy bleeding — gushing, very heavy and prolonged periods.