What Is A Fibroid?

A fibroid is a noncancerous tumor that grows from the muscle tissue of the uterus. It is the most common benign pelvic tumor in women of reproductive age. Many women have them without ever knowing, because most fibroids cause no symptoms at all.

The word “tumor” sounds alarming, so it helps to be clear up front. A fibroid is not cancer. It does not turn into cancer. It is a clump of uterine muscle and connective tissue that grew in a disorganized way. The medical term is leiomyoma, and you may also hear them called myomas.

What Is A Fibroid and Where Does It Grow?

A fibroid starts in the muscular wall of the uterus, called the myometrium. It can stay small or grow large enough to make the abdomen look pregnant. Fibroids can grow as a single lump or in clusters, and some women have many at once.

Doctors classify fibroids by where they sit in the uterus. This location explains most of the symptoms a woman may notice.

• Intramural fibroids grow within the muscular wall itself. These are the most common type.
• Subserosal fibroids bulge outward from the outer surface of the uterus. They can press on nearby organs like the bladder or bowel.
• Submucosal fibroids push into the inner cavity of the uterus, where a pregnancy would implant. These are less common but are the type most linked to heavy bleeding and fertility problems.
• Pedunculated fibroids hang from a stalk, either inside or outside the uterus.

Size varies widely. Some fibroids are smaller than a pea. Others can grow to the size of a grapefruit or larger. A fibroid does not spread to other parts of the body the way cancer can. It stays where it started.

How Common Are Fibroids?

Fibroids are extremely common. Research consistently shows that a large share of women develop them at some point during their reproductive years. Many estimates come from studies that looked at uteruses directly, which means they catch fibroids that never caused a symptom.

Age matters. Fibroids are most often found in women in their 30s, 40s, and early 50s, and they tend to shrink after menopause when estrogen levels fall. They are rare in women under 20.

Fibroids are more common in Black women than in white women, and they tend to appear earlier and grow larger in Black women. The reasons are not fully understood. Researchers have looked at genetic differences, hormone patterns, and environmental factors, but no single cause has been confirmed. This pattern is well documented across many studies and is not in dispute.

What Causes Fibroids?

No one knows exactly what causes a fibroid to start growing. The clearest driver is the hormone estrogen, along with progesterone. Fibroids grow when these hormones are high and shrink when they fall.

That connection is easy to see in the timing. Fibroids rarely appear before puberty. They tend to grow during the reproductive years. They often shrink after menopause. They can also swell during pregnancy, when hormone levels rise.

Genetics also play a role. Fibroids often run in families, and researchers have identified specific genetic changes inside fibroid tissue that differ from normal uterine muscle. Some fibroids grow faster than others for reasons that are not fully clear.

Other factors have been studied, including body weight, age at first period, and diet. The evidence for these is mixed and weaker than the evidence for hormones and genetics. It is fair to say that estrogen and heredity are the major known factors, and that many details remain unknown.

What Are the Symptoms of Fibroids?

Most fibroids cause no symptoms. When they do, the symptoms depend on the size, number, and location of the fibroids. This is why two women with fibroids of the same size can feel completely different.

The most common symptoms include:

• Heavy or prolonged menstrual bleeding, which can lead to anemia over time
• Pelvic pain or a dull ache in the lower belly
• A feeling of fullness or pressure in the pelvis
• Frequent urination or trouble emptying the bladder, caused by pressure on the bladder
• Constipation or a feeling of incomplete bowel movements
• Pain during sex
• An enlarged belly that can look like weight gain or pregnancy
• Lower back pain

Heavy bleeding deserves attention. Some women lose enough blood over months to develop iron-deficiency anemia, which brings fatigue, shortness of breath, and pale skin. If periods are soaking through protection quickly or lasting much longer than usual, that is a reason to see a clinician.

Submucosal fibroids, the ones that push into the inner cavity, are the type most often linked to heavy bleeding and to trouble getting or staying pregnant. Fibroids in other locations are less likely to affect fertility, though large ones can still cause problems.

How Are Fibroids Diagnosed?

Fibroids are often found by accident during a routine pelvic exam or an imaging test done for another reason. A clinician may feel an enlarged or irregular uterus during a pelvic exam.

Imaging confirms the diagnosis. Ultrasound is usually the first test, and it can show the size and location of most fibroids. If more detail is needed, an MRI can map the fibroids more precisely, which helps when surgery or other procedures are being considered.

In some cases, a clinician may suggest a procedure that looks inside the uterus, such as a hysteroscopy, to see submucosal fibroids directly. Blood tests for anemia are common when heavy bleeding is a concern.

One useful point: a fibroid is usually diagnosed on imaging alone, without a biopsy. That is because its appearance on ultrasound and MRI is distinctive. A biopsy is rarely needed unless the imaging looks unusual.

How Are Fibroids Treated?

Treatment depends on symptoms, not on the fibroid itself. Women with no symptoms often need nothing beyond regular checkups. Fibroids that are not causing problems can be watched over time.

When symptoms are bothersome, options fall into a few broad groups. The right choice depends on the size and location of the fibroids, the severity of symptoms, whether pregnancy is planned, and personal preference.

• Medications can reduce bleeding and, in some cases, shrink fibroids. Hormonal options and non-hormonal drugs are both used. These manage symptoms rather than removing the fibroids, and symptoms often return when the medication stops.
• Procedures that remove or destroy fibroids include surgical removal of the fibroids while keeping the uterus, and minimally invasive techniques that use heat or other methods to destroy fibroid tissue. These can preserve the uterus but carry a chance that fibroids grow back.
• Uterine artery embolization blocks the blood supply to fibroids, causing them to shrink. It is performed by an interventional radiologist and is not usually recommended for women who want to become pregnant.
• Hysterectomy, removal of the uterus, is the only treatment that permanently ends fibroids. It is a major surgery and ends the ability to carry a pregnancy.

No single option is best for everyone. The evidence supports several approaches, and the choice is genuinely individual. A clinician who knows the details of a specific case is in the best position to discuss trade-offs.

Do Fibroids Affect Fertility and Pregnancy?

Most women with fibroids get pregnant without difficulty. But some fibroids do affect fertility, mainly submucosal ones that distort the inner cavity where an embryo implants. Removing those fibroids can improve the chance of pregnancy in some women, though the evidence is not uniform across all studies.

During pregnancy, fibroids can grow and, in some cases, cause pain or complications. Many women with fibroids have normal pregnancies. The risk depends on the number, size, and location of the fibroids, and a clinician can assess this individually.

Key Takeaways

Fibroids are common, noncancerous growths of the uterine muscle. Most cause no symptoms and need no treatment. When symptoms appear, they usually involve heavy bleeding, pelvic pressure, or urinary and bowel changes. Diagnosis is typically made with imaging, and treatment ranges from watchful waiting to medication to surgery.

The most important thing to know is that a fibroid is not cancer and does not become cancer. If you have symptoms that concern you, especially heavy bleeding or pelvic pain, a clinician can help sort out what is going on and what, if anything, needs to be done.