Uterine fibroids (also called leiomyomas, fibromyomas or myomas) are benign (noncancerous) growths that develop on the outer or inner lining of the uterus. While many women with fibroids will have no symptoms, some may experience changes to their menstrual cycle, bleeding, pain, pressure and other complications related to pregnancy depending upon the type and size of the uterine fibroids.
Subserosal Fibroids
Subserosal fibroids develop on the outer wall of the uterus and expand outward. According to the American Society for Reproductive Medicine (ASRM), subserosal fibroids represent 55 percent of all fibroids cases. This type of fibroid may cause a sensation of generalized pressure in the pelvic or back area and can sometimes press on the bladder and interfere with normal urination. If the fibroids extend out of the posterior side of the uterus, they can cause constipation by pressing on the rectum, or they may cause back pain by pressing on the spinal nerves. Subserosal fibroids do not usually cause changes to menstruation.
Intramural Fibroids
Intramural fibroids represent approximately 44 percent of fibroids cases, according to the ASRM. They can be found in the muscular layers of the inner lining of the uterus. They expand inward and increase the size of the uterus. This expansion creates a larger surface area for bleeding and can lead to heavy menstrual bleeding and pelvic pain. They may also cause back pain and a generalized feeling of pressure in the pelvic region. The large size of the uterus is generally able to be felt on physical examination. Although fibroids are a rare cause of infertility (only 3 percent of all infertility is caused by fibroids, according to the ASRM), intramural fibroids can contribute to problems maintaining a pregnancy (miscarriage), early labor or other labor complications.
Submucosal Fibroids
The ASRM estimates that submucosal fibroids--those that occur just under the lining of the uterus and protrude into the uterine cavity--represent about 5 percent of all fibroids cases. While these fibroids are the rarest of the three types of uterine fibroids, they typically cause the most serious problems. They are known for causing heavy menstrual bleeding that may gush and continue for prolonged periods. Excessive bleeding can lead to anemia that, if left untreated, can lead to heart problems. According to the Mayo Clinic, submucosal fibroids may also create problems for women who are trying to get pregnant. Through their effects on the endometrium (lining of the uterine wall), submucosal fibroids may make it more difficult for a fertilized egg to implant itself, increasing the likelihood of miscarriage. According to the University of Maryland Medical Center (UMMC), they may put women who are already pregnant at higher risk of premature delivery, caesarian section, breech births and excessive bleeding after delivery.
Leiomyosarcoma
Leiomyosarcoma is a very rare type of cancer caused by uterine fibroids. The ASRM estimates that the odds of uterine fibroids being cancerous among women of reproductive age are about 1 in 1,000. Leiomyosarcoma is more common among postmenopausal women. According to the UMMC, rapidly enlarging fibroids, or fibroids that are growing at any rate among postmenopausal women, should be evaluated for cancer.
