A uterine fibroid is a noncancerous growth made of muscle and connective tissue that develops in or on the uterus. Fibroids are extremely common: by age 50, roughly 70% of white women and 80% of Black women will have them, based on ultrasound screening. Most fibroids cause no symptoms at all and are discovered incidentally during a routine exam or imaging for something else. When they do cause problems, the effects range from heavy periods and pelvic pressure to fertility challenges.
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, pushing against the lining. Even small submucosal fibroids can cause heavy bleeding.
- Subserosal fibroids grow on the outer surface of the uterus. Large ones can press on the bladder or rectum.
- Pedunculated fibroids are a subtype of either submucosal or subserosal fibroids that hang from a stalk, like a mushroom, inside or outside the uterus.
How Big Fibroids Can Get
Fibroids range from tiny seedlings invisible to the naked eye to masses that distort and enlarge the uterus. In general terms, small fibroids measure under 5 cm (about the size of a cherry to a golf ball), medium fibroids fall between 5 and 10 cm (plum to orange), and large fibroids exceed 10 cm, sometimes reaching the size of a grapefruit or watermelon. A single person can have one fibroid or dozens, and each may grow at a different rate.
What Causes Them to Grow
Fibroids are fueled by reproductive hormones. Estrogen was long considered the main driver, but more recent research shows that progesterone plays an equally significant role. Progesterone activates pathways inside fibroid cells that promote growth and survival, improves the blood supply feeding the fibroid, and modifies the connective tissue that makes up much of the fibroid’s bulk. This is why fibroids tend to grow during the reproductive years, when hormone levels are high, and typically shrink after menopause.
Genetics also play a clear role. Black women are nearly five times more likely to develop fibroids than white women and tend to develop them at younger ages, with larger sizes. Research also shows that Asian-Chinese women face a disproportionately higher risk compared to the general population.
Common Symptoms
Many fibroids produce no symptoms. When they do, heavy menstrual bleeding is the hallmark complaint. A normal period lasts about four to five days with roughly two to three tablespoons of blood loss. With fibroids, periods often stretch beyond seven days, and blood loss can double. Practical signs that your bleeding is heavy include soaking through a pad or tampon in under two hours, passing clots the size of a quarter or larger, needing to double up on pads, or waking at night to change protection.
Beyond bleeding, fibroids can cause pelvic pressure or a feeling of fullness in the lower abdomen, frequent urination (when a fibroid presses on the bladder), difficulty emptying the bladder completely, constipation, and lower back pain. Large fibroids sometimes make the abdomen visibly distended. The chronic blood loss from heavy periods can also lead to iron-deficiency anemia, leaving you fatigued, short of breath, or lightheaded.
Fibroids and Fertility
Not all fibroids interfere with getting pregnant, but location matters. Fibroids that change the shape of the uterine cavity or block the fallopian tubes can prevent sperm from reaching an egg or stop a fertilized egg from traveling into the uterus. Submucosal fibroids are particularly problematic because they can thin the uterine lining and reduce blood flow to the area where an embryo needs to implant.
During pregnancy, fibroids raise the risk of miscarriage, preterm delivery, and cesarean section. They can shift the baby’s position inside the uterus and, in some cases, outgrow their own blood supply, causing sudden, severe pain. These risks don’t affect every pregnancy with fibroids, but they’re worth discussing with a provider if you’re planning to conceive.
How Fibroids Are Diagnosed
Pelvic ultrasound is the standard first step. A combination of abdominal and transvaginal ultrasound gives the clearest initial picture, showing fibroid size, number, and location. Doppler imaging, which measures blood flow, is typically included and helps distinguish a fibroid growing on the outside of the uterus from other pelvic masses by identifying characteristic “bridging” blood vessels between the growth and the uterine wall.
When ultrasound doesn’t provide enough detail, or when surgery is being planned, MRI offers a more precise map. MRI can assess whether a fibroid is solid and well-supplied with blood or has started to degenerate, which influences treatment decisions. For fibroids growing into the uterine cavity, a saline infusion sonohysterography (where sterile saline is gently infused into the uterus during ultrasound) helps define the boundary between a fibroid and other conditions like polyps.
Are Fibroids Ever Cancerous?
The short answer is that fibroids themselves are benign. A rare uterine cancer called leiomyosarcoma can look like a fibroid on imaging, but the actual incidence among women who go to surgery for presumed fibroids is very low. A recent meta-analysis put the rate at roughly 0.12 to 0.51 per 1,000 procedures. Rapid growth alone is not a reliable sign of cancer, though unusually fast changes are still worth evaluating.
Treatment Options
Treatment depends on your symptoms, your plans for pregnancy, and how much the fibroids affect your daily life. If fibroids aren’t causing problems, monitoring them over time with periodic ultrasound is a perfectly reasonable approach.
Medication
Hormonal treatments can manage symptoms like heavy bleeding and pelvic pain. Some options work by lowering estrogen and progesterone levels, temporarily shrinking fibroids or stopping periods. These are often used as a bridge, either to relieve symptoms while you decide on a longer-term plan or to shrink fibroids before surgery.
Myomectomy
Myomectomy removes fibroids while leaving the uterus intact, making it the preferred option for women who want to preserve fertility. It can be performed through a small incision, through the vagina (for submucosal fibroids), or through a traditional abdominal incision depending on fibroid size and location. Compared to less invasive alternatives, myomectomy is associated with better quality-of-life outcomes and a lower risk of needing a repeat procedure down the road.
Uterine Artery Embolization
This minimally invasive procedure cuts off the blood supply to fibroids by injecting tiny particles into the uterine arteries. Fibroids then shrink over weeks to months. Recovery is faster than surgery, but the reintervention rate is higher: women who undergo embolization are roughly three times more likely to need another procedure compared to those who have a myomectomy. Both procedures carry similar rates of serious complications, which are low overall.
Hysterectomy
Removing the uterus entirely is the only treatment that eliminates fibroids permanently with no chance of recurrence. It’s typically considered when symptoms are severe, other treatments haven’t worked, or there’s no desire for future pregnancy.
What Affects Your Specific Outlook
Fibroids are not a one-size-fits-all condition. A 2 cm intramural fibroid found incidentally on ultrasound may never need treatment, while a 4 cm submucosal fibroid could cause disabling bleeding. Growth rates vary too. Some fibroids remain stable for years, others grow steadily, and many shrink significantly once menopause arrives and hormone levels drop. The combination of fibroid type, location, size, your symptoms, and your life plans all shape which path makes the most sense.