A fibroid is a noncancerous growth made of muscle and fibrous tissue that develops in or on the uterus. Fibroids range from the size of a seed to the size of a melon, and you can have one or several at the same time. They’re extremely common: by age 50 to 54, roughly 16% of women have been diagnosed with them, though many more likely have fibroids without knowing it because small ones 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 and treatment.
- 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, where they’re most likely to cause heavy bleeding.
- Subserosal fibroids grow on the outer surface of the uterus and tend to press on nearby organs like the bladder or bowel.
- Pedunculated fibroids are submucosal or subserosal fibroids that hang from a stalk, either inside or outside the uterus.
What Causes Them to Grow
Fibroids are driven primarily by hormones. Progesterone plays a central role: it activates pathways that make fibroid cells multiply, builds up the blood supply feeding the fibroid, and promotes the production of tough, fibrous tissue that gives fibroids their structure. Estrogen contributes as well. This hormonal dependence is why fibroids typically shrink after menopause, when hormone levels drop.
Several factors raise your risk. Black women are disproportionately affected, with a prevalence of about 18.5% compared to other racial and ethnic groups. Other risk factors include obesity, high blood pressure, a family history of fibroids, vitamin D deficiency, never having been pregnant, and older age. Pregnancy and long-term use of hormonal contraceptives appear to lower the risk.
Common Symptoms
Many fibroids cause no symptoms and are discovered incidentally during a routine pelvic exam or imaging for something else. When symptoms do occur, they typically include:
- Heavy menstrual bleeding or painful periods
- Periods that last longer than usual or come more frequently
- Pelvic pressure or pain
- Frequent urination or difficulty emptying the bladder
- Constipation
- A visibly growing stomach area
- Lower back pain or pain during sex
The heavy bleeding fibroids cause can lead to anemia over time, which shows up as persistent tiredness and weakness. In rare cases, a fibroid can outgrow its blood supply and begin to die, causing sudden, sharp pain.
How Fibroids Are Diagnosed
Ultrasound is the first tool most doctors reach for. A technician places a device on your abdomen or inserts a small probe into the vagina to create images of the uterus, which can confirm fibroids and measure them. If the ultrasound doesn’t provide enough detail, an MRI can map the exact size, location, and type of each fibroid more precisely. MRIs are most often used when the uterus is large or when a woman is approaching menopause.
For fibroids that affect the inner cavity of the uterus, especially in cases of heavy bleeding or difficulty getting pregnant, a doctor may use a procedure that fills the uterine cavity with sterile salt water to get clearer images of the lining and any submucosal fibroids pressing into it.
How Big Can They Get
Fibroids vary enormously. Small ones, under 5 centimeters, are roughly the size of a pea to a golf ball. Medium fibroids, between 5 and 10 centimeters, are comparable to a lemon or an orange. Large fibroids exceed 10 centimeters and can reach the size of a grapefruit or even a melon. The average fibroid at diagnosis falls in the 5 to 10 centimeter range. Size alone doesn’t determine whether treatment is needed. A small submucosal fibroid inside the uterine cavity can cause far more bleeding than a large subserosal one sitting quietly on the outer wall.
Effects on Fertility and Pregnancy
Not all fibroids interfere with fertility, but certain types do. Submucosal fibroids and large intramural fibroids (greater than 6 centimeters) are the most likely to reduce your chances of conceiving. They can distort the shape of the uterine cavity, block the fallopian tubes, or interfere with a fertilized egg implanting properly. Changes in the shape of the cervix can also reduce the number of sperm that reach the uterus.
During pregnancy, the biggest concern is an increased chance of preterm birth or miscarriage. Fibroids can shift the baby’s position, raising the likelihood of a cesarean delivery. They can also outgrow their blood supply during pregnancy and cause severe pain, though this is uncommon.
Treatment Options
Treatment depends on how much your symptoms affect daily life, whether you want to become pregnant, and the size and location of the fibroids. Small, symptom-free fibroids often need no treatment at all and are simply monitored over time.
When treatment is needed, options range from medication to surgery. Hormonal treatments can slow fibroid growth and reduce bleeding. For more definitive results, two minimally invasive procedures avoid traditional surgery entirely. Uterine fibroid embolization (UFE) cuts off the blood supply to fibroids by injecting tiny particles into the arteries that feed them. Nearly 90% of patients who undergo UFE experience significant or complete relief from their symptoms. Another option, focused ultrasound guided by MRI, uses targeted pulses of ultrasound energy to heat and destroy fibroid tissue. Most patients see significant symptom improvement within six months, with relief lasting at least three years.
Surgical options include myomectomy, which removes the fibroids while preserving the uterus (important for those who want to become pregnant), and hysterectomy, which removes the uterus entirely and is the only treatment that guarantees fibroids won’t return. The choice between these depends heavily on your personal goals and the specifics of your fibroids, so it’s worth understanding all the options before deciding.