Uterine fibroids: Basic guide

What are uterine fibroids? They are very common non-cancerous tumors that grow within the wall of the uterus, and are most often found among women of reproductive age.

Fibroids, known technically as leiomyomata, can vary in size and number, and often cause no symptoms at all. But when they are noticed, pain, heavy bleeding and pelvic pressure are just a few of the things women may experience.

Types of fibroids in the uterus by NIH Medical Arts

What are uterine fibroids?

Fibroids may grow as a single tumor or in clusters. A single fibroid can be microscopic in size, or can grow to eight inches or more across, though most fibroids range from about the size of a large marble to slightly smaller than a baseball. In many cases, a single uterus can contain many fibroids.

Bunches or clusters of fibroids are often of different sizes. Not all fibroids grow — some may shrink, while others might remain constant over time.

Healthcare providers categorize fibroids based on where they grow:

  • Submucosal fibroids grow just underneath the uterine lining and into the endometrial cavity.
  • Intramural fibroids grow inside the muscular wall of the uterus.
  • Subserosal fibroids grow on the outside of the uterus.

Some fibroids grow on stalks that emerge from the surface of the uterus or into the cavity of the uterus, and are called pedunculated fibroids.

Fibroid signs and symptoms

​Uterine fibroids can cause uncomfortable or sometimes painful symptoms, such as:

  • Heavy bleeding or painful periods
  • Anemia
  • Bleeding between periods
  • Feeling “full” in the lower abdomen (pelvic pressure)
  • Frequent urination (caused by a fibroid pressing on the bladder)
  • Abdominal pain
  • Lower back pain
  • Pain during sex
  • Reproductive problems, such as infertility, multiple miscarriages, and early onset of labor during pregnancy
  • Obstetrical problems, such as increased likelihood of cesarean section
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However, it’s important to note that many women have no symptoms of fibroids.

How are uterine fibroids diagnosed?

Unless you have symptoms, you probably won’t know that you have uterine fibroids.



Large intramural fibroidSometimes, health care providers find fibroids during a routine gynecological exam. During this exam, the health care provider checks the size of your uterus by putting two fingers of one hand into the vagina while using the other hand to press lightly on your abdomen.

If you have fibroids, your uterus may feel larger than normal or it may feel irregularly shaped. But even small growth in the uterus may cause considerable symptoms and heavy periods leading to anemia. Smaller fibroids that can’t be found through a routine manual examination can be detected with ultrasound.

If your health care provider thinks you have fibroids, he or she may use one or more types of imaging technology to confirm the diagnosis.

Some common types of imaging technology are:
  • Ultrasound, which uses sound waves to form the picture
  • Saline infusion sonography, which uses an injection of salt solution into the uterus to help create the ultrasound image
  • Magnetic resonance imaging (MRI), which uses magnets and radio waves to create the picture
  • X-­rays, which use a form of electromagnetic radiation to “see” into the body
  • Computed tomography (CT) or computer-assisted tomography (also called a “CAT” scan), which scans the body with X-rays from many angles to create a more complete picture
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We don’t know what causes uterine fibroids. Scientists have a number of theories, but none of these ideas explains these uterine growths completely.

Some factors researchers believed to be related to fibroid growth are:

  • Estrogen
  • Progesterone
  • Growth hormones
  • Genetic changes
  • Misplaced cells present in the body before birth

Other factors that may affect fibroid growth:

  • Quantity of micronutrients — nutrients, such as iron, that the body needs only small amounts of — in the blood. For instance, a deficiency of vitamin D may be associated with uterine fibroids.
  • Major stresses

It is likely that fibroids are caused by many factors interacting with one another. Once we know the cause or causes of these tumors, our efforts to find a cure or even prevent fibroids could move ahead more quickly.

How many women are affected by uterine fibroids?

One study found that between 80% and 90% of African American women and 70% of white women will develop fibroids by age 50. Some may have no symptoms, however, hundreds of thousands of women seek treatment for fibroids each year.

Research shows that over 90% of women who are newly diagnosed will seek medical or surgical treatment for the condition within a year of the diagnosis. In 2000, more than 250,000 hospital admissions were related to uterine fibroids.

Every year, fibroids lead to more than 200,000 hysterectomies. Women who wish to have children have the option of myomectomy, a surgical procedure that removes the timors while leaving the uterus intact.

Which women are at risk of uterine fibroids?

Fibroids usually grow in women of childbearing age. Among US women ages 25 to 44, about 30% have symptoms of fibroids. Affected African American women are more likely to have multiple tumors. We don’t know exactly how many new cases of fibroids occur in a year, as they may not cause any symptoms, but clearly millions of American women have them at any one time.

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There have been reports of rare cases in which young girls, who have not yet started their periods (pre­pubertal), had small fibroids. For African American women, fibroids typically develop at a younger age, grow larger, and cause more severe symptoms.

Fibroids may shrink after menopause. However, research shows that they are more likely to shrink in postmenopausal white women than in premenopausal black women.

Several factors affect a woman’s risk for having uterine fibroids. Factors that increase the risk of fibroids:

  • Age older than 40 years
  • African American race
  • Obesity
  • Family history of uterine fibroids
  • High blood pressure
  • No history of pregnancy
  • Low levels of vitamin D

Factors that lower the risk of fibroids:

  • Pregnancy (the risk decreases with increasing number of pregnancies)
  • Long-term use of progestin-only birth control pills or oral contraceptives
  • Use of the birth control shot (depot medroxyprogesterone acetate [DMPA], or Depo-Provera)
How are fibroids treated?

Hysterectomy — the removal of the uterus — is the only certain cure for uterine fibroids. But it’s important to note: That is not the only treatment option, and it is not the best treatment for every woman with fibroids.

Read more in this article: How uterine fibroids are treated





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