A Beginner’s Guide to Uterine Fibroids

What Are Uterine Fibroids and Why Do They Develop?

Uterine fibroids, also called leiomyomas or myomas, are benign tumors made of smooth muscle cells and fibrous connective tissue that form in or on the muscular wall of the uterus.^[1] They are not cancerous, and research shows fibroids do not become cancerous over time. Some uterine masses that resemble fibroids on imaging can, in rare cases, require further evaluation, which is one reason imaging confirmation matters for an accurate diagnosis.

Fibroids develop when a single smooth muscle cell in the uterine wall begins dividing repeatedly, gradually forming a solid, rounded mass distinct from the surrounding tissue.^[2] Estrogen and progesterone, the hormones that regulate the menstrual cycle, are well-established drivers of fibroid growth. This explains why fibroids most often develop during reproductive years, may grow more rapidly during pregnancy when hormone levels are elevated, and typically stop growing after menopause when hormone production declines.

What Symptoms Do Fibroids Cause?

Not every fibroid causes noticeable symptoms. Research indicates that only about 25% to 30% of women with fibroids experience symptoms significant enough to consider treatment.^[3] When fibroid symptoms do occur, the most common include:

• Heavy or prolonged menstrual bleeding, sometimes with clots
• Pelvic pain or pressure
• Frequent urination or difficulty emptying the bladder completely
• Constipation or bloating
• Lower back or leg pain
• Fatigue linked to iron-deficiency anemia from ongoing heavy blood loss

Symptom severity is more closely tied to a fibroid’s size, number, and exact location within the uterus than to the diagnosis alone. A small fibroid positioned inside the uterine cavity can cause significant bleeding, while a much larger fibroid on the outer uterine wall may cause no symptoms at all.

Many women find their symptoms have been attributed to normal menstrual variation. A pelvic exam or ultrasound can help determine what is actually happening, and getting a clear answer is often the first step toward relief.

What Are the Different Types of Uterine Fibroids?

Fibroids are classified by where they grow in relation to the uterine wall. Location often determines which symptoms appear. For a detailed comparison of all fibroid types, see all types of uterine fibroids.

Intramural Fibroids

Intramural fibroids develop within the muscular wall of the uterus and are the most common fibroid type. Depending on their size, they can enlarge the uterus overall and contribute to heavy bleeding, pelvic pressure, or a feeling of abdominal fullness.

Subserosal Fibroids

Subserosal fibroids grow on the outer surface of the uterus, facing outward toward the pelvic cavity. Because they grow away from the uterine lining, they tend to have less direct effect on menstrual bleeding but can press on the bladder or bowel as they enlarge.^[4]

Submucosal Fibroids

Submucosal fibroids grow just beneath the inner lining of the uterus (the endometrium) and are the fibroid type most likely to cause heavy, prolonged menstrual bleeding and fertility-related concerns. Even small submucosal fibroids can significantly affect menstrual patterns.^[4]

Pedunculated Fibroids

Pedunculated fibroids attach to the uterus by a thin stalk rather than growing directly from the wall. They can be subserosal (growing outward) or submucosal (growing into the uterine cavity). The stalk can sometimes twist, which may cause sudden, sharp pelvic pain.

What Is a Fundal Fibroid?

A fundal fibroid develops at the fundus, the upper, dome-shaped portion of the uterus where the fallopian tubes meet.^[5] Fundal fibroids are not a separate structural category. They can be intramural, subserosal, or submucosal depending on how deep they grow within the uterine wall at that location. Their position at the top of the uterus can sometimes influence fundal height measurements taken during prenatal monitoring.

Do Fibroids Only Grow in the Uterus?

Fibroids form specifically from uterine smooth muscle tissue, so by definition they can only develop in or on the uterus itself.^[6] Growths found on the ovaries or elsewhere in the pelvis, such as ovarian cysts, are made of entirely different tissue and are not classified as fibroids, even though the pelvic pressure, bloating, and discomfort they cause can feel similar. This is one reason imaging that specifically visualizes the uterus is the most reliable way to confirm what is causing your symptoms.

How Are Fibroids Diagnosed?

Fibroids are often discovered during a routine pelvic exam when a provider notices an irregular or enlarged uterus. If fibroids are suspected, imaging is ordered to confirm the diagnosis, identify fibroid locations, and assess size. For a full walkthrough of the diagnostic process, see how fibroids are diagnosed.

Pelvic Exam

During a pelvic exam, a provider may feel an enlarged or irregularly shaped uterus that suggests fibroid growth. This is often the first step that leads to imaging for confirmation.

Pelvic Ultrasound

Ultrasound is the most common first-line imaging tool for diagnosing fibroids. A transducer placed on the abdomen or inserted into the vagina produces images that show the uterus and any visible growths.^[7] Ultrasound can confirm fibroid presence and provide initial size and location information.

MRI Imaging

Magnetic resonance imaging (MRI) provides more detailed information than ultrasound, including the precise number, size, and location of fibroids. MRI is commonly used when a more complete picture is needed, including when evaluating whether a patient may be a candidate for UFE.

Who Is Most at Risk for Developing Fibroids?

Several factors are associated with a higher likelihood of developing fibroids. For a complete overview, visit the fibroid risk factors page.

• Age: Fibroids are most common in women in their 30s and 40s and rarely develop before puberty or after menopause.
• Family history: Having a mother or sister who has had fibroids significantly increases risk.^[1]
• Race and ethnicity: Black women develop fibroids at significantly higher rates than women of other racial backgrounds and often at younger ages. Research indicates prevalence in Black women may reach 80% by age 50.^[3] The reasons behind this disparity are still being studied, including genetic, environmental, and systemic factors.
• Obesity: Body weight above a healthy range is associated with higher fibroid risk.
• Vitamin D deficiency: Some research suggests a potential link between lower vitamin D levels and fibroid development, though more study is ongoing.

Understanding your personal risk profile is one reason a conversation with a fibroid specialist can be worthwhile, even before symptoms become disruptive.

What Fibroid Treatment Options Are Available?

Not all fibroids require treatment. When symptoms are absent or mild, a watchful waiting approach with regular monitoring may be appropriate. For women whose fibroid symptoms interfere with daily life, work, or sleep, non-surgical treatment options can address the underlying problem without removing the uterus.

Uterine Fibroid Embolization (UFE) is a minimally invasive, outpatient procedure performed by an interventional radiologist. During UFE, a small catheter is guided through the blood vessels to the uterine arteries, where tiny embolic particles are injected to block the blood supply feeding the fibroids. Without adequate blood supply, fibroids gradually shrink over the following weeks and months.^[8]

UFE preserves the uterus entirely and does not require general anesthesia or a large incision. Most patients return to normal activities within one to two weeks. UFE treats multiple fibroids at the same time, including those that may be too small to detect individually.

UFE addresses the fibroids that exist at the time of the procedure by targeting their blood supply. It does not prevent new fibroids from developing later. A fibroid specialist can help determine whether UFE may be appropriate for your individual situation.