A fibroid is a noncancerous growth that develops in or on the uterus. Fibroids are made of smooth muscle cells and connective tissue, and they range from the size of a seed to larger than a grapefruit. They’re remarkably common: by age 50, roughly 80% of Black women and 70% of White women will have developed at least one, though many never know it because fibroids often cause no symptoms at all.
Where Fibroids Grow
Fibroids are classified by their location in the uterus, and that location matters more than size when it comes to symptoms.
- Intramural fibroids grow within the muscular wall of the uterus. These are the most common type.
- Submucosal fibroids grow into the inner cavity of the uterus. Even small ones can cause heavy bleeding because they distort the uterine lining.
- Subserosal fibroids grow on the outer surface of the uterus. Large ones can press on nearby organs like the bladder or rectum.
- Pedunculated fibroids are submucosal or subserosal fibroids that hang from a stalk, either inside or outside the uterus.
A single person can have multiple fibroids of different types at the same time.
What Causes Fibroids to Develop
The hormones estrogen and progesterone are the primary drivers of fibroid growth. Estrogen increases the number of progesterone receptors in uterine tissue, essentially making cells more responsive to progesterone. Progesterone then stimulates those cells to multiply, and it also promotes the formation of new blood vessels that feed the growing fibroid with oxygen and nutrients.
This is why fibroids typically develop during the reproductive years, when hormone levels are highest, and why they tend to shrink after menopause. Genetics play a role too. Mutations in a specific gene called MED12 appear in many fibroids and may help trigger the abnormal cell growth in the first place. If your mother or sister had fibroids, your risk is higher.
Common Symptoms
Many fibroids are completely silent. When they do cause problems, the most common symptom is heavy or prolonged menstrual bleeding, sometimes severe enough to cause anemia. Bleeding between periods also occurs.
Beyond bleeding, fibroids can create a sensation of fullness, pressure, or bloating in the lower abdomen. A large fibroid can make the belly look visibly enlarged. Other symptoms depend on what the fibroid is pressing against: frequent urination or difficulty fully emptying the bladder when it pushes on the bladder, and constipation or rectal pressure when it pushes on the bowel. Pain during periods or during sex is also possible, though not universal.
How Fibroids Are Diagnosed
Fibroids are often discovered by accident during a routine pelvic exam, when a doctor notices the uterus feels irregular in shape or larger than expected. From there, ultrasound is the standard first step. A technician may use an external probe on the abdomen or an internal probe inserted into the vagina to map the number, size, and location of fibroids.
If ultrasound doesn’t give a clear enough picture, an MRI can show more detail. MRI is particularly useful for people with a larger uterus or those approaching menopause, because it can distinguish fibroids from other types of growths and help guide treatment planning. For fibroids that grow into the uterine cavity, a procedure that fills the uterus with saline during ultrasound can improve the image. A hysteroscopy, where a thin lighted camera is passed through the cervix, gives a direct view of the inside of the uterus.
Fibroids and Cancer Risk
Fibroids are benign, and the vast majority stay that way. A rare cancer called leiomyosarcoma can look like a fibroid on imaging, which is why the question comes up. For women under 50, the chance that a presumed fibroid is actually cancerous is about 1 in 770. That risk rises with age: for women over 60, it’s closer to 1 in 65. There’s no reliable way to distinguish the two on ultrasound alone, which is one reason doctors monitor larger or rapidly changing fibroids more closely.
Effects on Fertility and Pregnancy
Fibroids are found in 5 to 10% of women experiencing infertility, but they’re the sole cause of infertility in only about 1 to 2% of cases. The impact depends heavily on location. Submucosal fibroids, the type that grows into the uterine cavity, are the most likely to interfere with implantation or pregnancy. Intramural and subserosal fibroids are less disruptive unless they’re very large.
During pregnancy, complications occur in roughly 10 to 40% of women who have fibroids. The risk of miscarriage is about 1.7 times higher compared to women without fibroids, and fibroids larger than 3 centimeters carry greater risk. Women with fibroids are also nearly four times more likely to have a baby in breech position, and rates of cesarean delivery, premature labor, and postpartum hemorrhage are all elevated. None of this means pregnancy with fibroids is impossible. Many women carry healthy pregnancies with fibroids present, but close monitoring helps catch problems early.
Treatment Without Surgery
If fibroids aren’t causing symptoms, they typically don’t need treatment. Monitoring with periodic ultrasounds is enough. For bothersome symptoms, medication can help manage bleeding and discomfort. Hormonal options like birth control pills or IUDs can reduce heavy periods, though they don’t shrink the fibroids themselves.
A class of medications that suppresses the hormones driving fibroid growth can shrink fibroids and stop periods temporarily, but side effects like bone loss, hot flashes, and vaginal dryness limit their use to about six months without additional hormone support. Once the medication stops, fibroids typically regrow to their previous size. A newer version of these medications can be used for up to two years with hormonal add-back therapy to offset side effects, though it controls bleeding rather than shrinking the fibroids.
Surgical and Procedural Options
When symptoms are severe or fibroids are very large, more definitive treatment may be needed. The three main options are myomectomy, uterine fibroid embolization, and hysterectomy.
Myomectomy surgically removes the fibroids while leaving the uterus in place. It’s often preferred for people who want to preserve fertility. Recovery takes several weeks depending on whether the surgery is done through a large incision or with minimally invasive techniques. New fibroids can grow after a myomectomy.
Uterine fibroid embolization (UFE) is a nonsurgical alternative. An interventional radiologist threads a thin catheter into the arteries that supply the uterus and releases tiny particles that block blood flow to the fibroids. Starved of their blood supply, the fibroids shrink or disappear. A seven-year follow-up study found that UFE and myomectomy had similar effectiveness, but UFE had fewer complications and shorter hospital stays. About 9% of women who had UFE needed a second procedure, compared to 10% after myomectomy. Miscarriage rates were similar between the two groups.
Hysterectomy, the removal of the uterus, is the only treatment that eliminates fibroids permanently. It’s typically reserved for people with severe symptoms who don’t plan future pregnancies.
What Happens After Menopause
Because fibroids depend on estrogen and progesterone to grow, they generally shrink once hormone levels drop during menopause. Symptoms like heavy bleeding stop entirely. For many women in their 40s with moderate symptoms, this natural hormonal shift makes watchful waiting a reasonable strategy, since the problem may resolve on its own within a few years.