How Fibroids Affect Fertility and Pregnancy

Why Uterine Fibroids Sometimes Cause Pregnancy Complications

Doctor examining pregnant patient's belly
Getty Images/Ariel Skelley

A fibroid is a lump of muscle tissue that grows in the wall of the uterus in many women and can sometimes cause pregnancy complications such as pain, infertility, miscarriage or preterm labor

What Are Fibroids?

Fibroids are muscular tumors that may develop in the wall of a woman's womb. They are usually benign, meaning they are not cancerous. Fewer than 1 in 1,000 fibroids are cancerous. 

Fibroids fall into one of four categories based on the location of the growth:

  • Intramural: in the wall of the uterus
  • Subserosal: on the outside of the uterus
  • Submucosal: in the uterine cavity
  • Pedunculated: outside the uterus attached by a stem

Fibroids range from small (seed sized) to large (grapefruit sized). Women who develop them may have one or several of the tumors. 

Women at Risk 

Fibroids are very common. By age 35, 40 to 60 percent of women have them. By age 50, the incidence jumps to 70 to 80 percent. 

Fibroids are most common in women in their 30s, 40s and early 50s and in African American women, although women of all races can develop them. Having a family member with fibroids or being overweight or obese also puts women at greater risk of fibroids.  

Why some women develop fibroids and others don't is unknown. Genetics and hormones appear to play a role. 

How Fibroids Can Affect Your Health

Fibroids are usually not dangerous to a woman's health, although they may affect her quality of life.

Some women experience no symptoms from their fibroids and may not even know they have them.

Women who do have symptoms may experience: 

  • long periods, heavy menstrual bleeding and/or menstrual pain
  • bleeding between periods
  • anemia
  • pressure on the bladder, causing frequent urination 
  • pressure on the rectum, causing constipation or difficult bowel movements
  • an enlarged lower abdomen and a feeling of fullness
  • lower back pain
  • painful sex

Fibroids and Pregnancy Complications

Usually, women with fibroids have normal pregnancies. However, in some women (10 to 30 percent), fibroids cause complications with pregnancy or labor. These problems can include: 

  • infertility, although fibroids are usually not the cause of fertility problems
  • bleeding early in the pregnancy
  • pain, most often in women with fibroids that are larger than 5 centimeters during the second and third trimesters 
  • miscarriage

In about a third of women, fibroids grow during the first trimester of pregnancy. 

The Link Between Fibroids and Miscarriage

Although most pregnancies with fibroids are normal, the tumors can cause miscarriages, especially early in pregnancy. The miscarriage rate for women with fibroids is 14 percent vs 7.6 for women who do not have fibroids.

 The risk of a miscarriage appears to increase with multiple fibroids. How fibroids cause miscarriage is unknown. One factor may be that the tumors restrict blood supply to the developing placenta and fetus. 

Do Fibroids Need to Be Treated?

If you don't have symptoms, your doctor may just keep an eye on the size of your fibroids.

Sometimes surgery (or other methods of shrinking or destroying the tumors) is recommended for fibroids that are causing moderate to severe symptoms or pregnancy complications. For example, if it's suspected that your fibroids are contributing to fertility problems or recurrent miscarriages, you can talk to your doctor about removing them. You should be aware, however, that it's unclear if removing fibroids helps improve fertility or prevent miscarriages. 

Pain and heavy menstrual bleeding from fibroids can be treated with over-the-counter pain medications, hormonal birth control such as birth control pills or a progestin–releasing intrauterine device (IUD). If you're anemic from heavy bleeding, your doctor may recommend iron pills to restore your levels of this nutrient. 

Sources:

Uterine fibroids fact sheet. WomensHealth.gov. January 15, 2015.

Uterine Fibroids. MedlinePlus. U.S. National Library of Medicine. January 8, 2016. 

Frequently Asked Questions: Uterine Fibroids. The American College of Obstetricians and Gynecologists. May 2011. 

Lee, H.J., Norwitz, E.R., and Shaw, J. (2010). Contemporary Management of Fibroids in Pregnancy. Reviews in Obstetrics & Gynecology. 

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