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A subserosal fibroid is a noncancerous growth on the outer wall of the uterus. It forms under a layer of tissue called the serosa. It grows outward, not into the uterus. This can cause symptoms that differ from other fibroid types. Understanding how a subserosal fibroid affects the body can help you recognize symptoms and explore treatment options.
Quick facts
- Subserosal fibroids grow on the outer wall of the uterus, under the serosa, rather than into the uterine cavity[1]
- They are less likely to cause heavy bleeding than fibroids that grow closer to the uterine lining[1]
- A subserosal fibroid is generally considered large once it reaches about 10 centimeters, roughly the size of a grapefruit
Subserosal fibroids rarely affect the uterine lining. They usually do not cause heavy periods. Their symptoms come from the fibroid itself, not the lining. The fibroid presses on nearby pelvic organs, and that pressure is what causes most symptoms.
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What Is a Subserosal Fibroid?
Subserosal fibroids grow just under the serosa, the smooth outer layer of the uterus. They do not grow into the uterine cavity. Instead, they push outward into the pelvic space. This spot sets them apart from other fibroid types. It also helps explain why symptoms can feel different.
Where a Subserosal Fibroid Can Grow
Subserosal fibroids are grouped by where they sit on the uterus:
- A fundal subserosal fibroid grows on top of the uterus, called the fundus.
- An anterior subserosal fibroid grows on the front of the uterus.
- A posterior subserosal fibroid grows on the back of the uterus.
- A pedunculated subserosal fibroid grows on a thin stalk from the outer surface of the uterus.
Learn more about the different types of fibroids to see how location and attachment affect your symptoms.
How Does a Subserosal Fibroid Affect Symptoms?
Subserosal fibroids grow on the outside of the uterus. So their symptoms often come from pressure on nearby organs, not changes inside the uterus. As they grow, they can press against the bladder, bowel, nerves, or nearby tissue. This pressure can lead to discomfort.
Subserosal fibroids are less likely to cause heavy periods than fibroids closer to the uterine lining.[1] Instead, symptoms are often tied to the fibroid’s size and location.
Common Symptoms of Subserosal Fibroids
Depending on where the fibroid sits, symptoms may include:
- A feeling of fullness or heaviness in the lower abdomen
- Pelvic pressure or pain
- Lower back or leg pain
- Pain during sex
- Frequent urination
- Constipation or difficulty with bowel movements
For example, a fibroid pressing on the bladder may cause more frequent urination. One pressing on the bowel may contribute to constipation. A pedunculated fibroid can sometimes twist on its stalk, causing sudden, severe pain.
These symptoms can look like other conditions. It helps to track any changes and talk with a fibroid specialist.
Not sure what your symptoms mean?
What Causes a Subserosal Fibroid?
Doctors have not found one single cause. Fibroid growth is tied to estrogen and progesterone, hormones that rise and fall during your reproductive years.[2] Genetics may play a role too. A family history of fibroids, along with age and body weight, may raise your risk. None of these factors mean a fibroid will form for sure.
Is a Subserosal Fibroid Dangerous?
A subserosal fibroid isn’t dangerous, but it can cause real discomfort. This can include abdominal cramping, pain in the lower back and legs, and pain during sex. Subserosal fibroids sit outside the uterus. Because of this, they tend to be less risky during pregnancy than other fibroid types. A subserosal fibroid that grows during pregnancy can change the shape of the uterus. This may create challenges with fetal development. It may also affect delivery.
As a subserosal fibroid presses on other organs, it can lead to constipation and more frequent urination. It can also cause severe pain if it is pedunculated and the stalk twists.
How Is a Subserosal Fibroid Diagnosed?
A subserosal fibroid is often found during a pelvic exam. A provider may notice the uterus feels larger or an odd shape. Imaging tests confirm this and show where the fibroid sits:
- Ultrasound: Usually the first test. It gives a general view of the uterus and any fibroids.
- MRI: Gives a more detailed picture. It can help tell a subserosal fibroid apart from other growths.
Ultrasound alone can sometimes miss a fibroid outside the uterus. An MRI may give a clearer picture.
Treatment Considerations for a Subserosal Fibroid
Treatment depends on the fibroid’s size, location, and the symptoms it causes. Subserosal fibroids are often linked to pressure symptoms like pelvic discomfort, frequent urination, or constipation. Some women may also have heavy bleeding or other symptoms.
Uterine Fibroid Embolization (UFE) is a minimally invasive treatment offered by USA Fibroid Centers. UFE works by blocking the blood supply to fibroids. This causes them to shrink over time.[2]
As fibroids shrink, many women feel relief from pelvic pressure, pain, heavy bleeding, and urinary frequency. UFE treats fibroids through their blood supply. This can make it an option for many types of fibroids, including subserosal fibroids in different areas of the uterus.
UFE is done as an outpatient procedure. Many patients return to light activities within a short time.
Learn more about Uterine Fibroid Embolization (UFE) to see whether this treatment path may be right for your situation.
Curious whether UFE is available near you?
How a Subserosal Fibroid Can Affect Pregnancy
Subserosal fibroids grow outside the uterine cavity. Because of this, they usually cause fewer pregnancy problems than fibroids inside the lining.[1] Still, a fibroid can grow larger during pregnancy. This can change the shape of the uterus. It may affect the baby’s position in some cases. If you are pregnant or planning to become pregnant and have a subserosal fibroid, talk with a specialist about monitoring. Our fibroids and pregnancy resource covers this topic in more depth.
FAQs About Subserosal Fibroids
Treatment option: UFE
Where Your Fibroid Grows Matters
A subserosal fibroid’s location outside the uterus can bring some relief when it comes to heavy bleeding, but the pressure it places on nearby organs can still affect your daily comfort.
Uterine Fibroid Embolization is a minimally invasive, outpatient option that works on fibroids regardless of where they sit on the uterus. A fibroid specialist can help you understand whether UFE may be right for your situation.
- Office on Women’s Health, “Uterine Fibroids,” U.S. Department of Health and Human Services, womenshealth.gov/a-z-topics/uterine-fibroids
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, “Uterine Fibroids,” nichd.nih.gov/health/topics/uterine
Medical disclaimer: This article is for educational purposes and not a substitute for professional medical advice. USA Fibroid Centers does not diagnose medical conditions or provide treatment recommendations. Please consult a physician for medical evaluation and treatment planning. Information in this article reflects current medical understanding but is not guaranteed to be complete or accurate.