Pregnancy changes nearly every system in a woman’s body, and uterine fibroids are no exception. The main reason fibroids grow during pregnancy is hormonal: levels of estrogen and progesterone rise dramatically, and these hormones can stimulate fibroid cells to enlarge. Blood flow to the uterus also increases, which may further support fibroid growth. This growth is common and often temporary, and many fibroids shrink again after delivery.
What Causes Fibroids To Grow During Pregnancy?
Estrogen and progesterone are the primary drivers. Fibroids are hormone-sensitive tumors, meaning their cells respond to the shifting hormonal environment of pregnancy. When these hormone levels climb, fibroid tissue can respond by growing larger.
Progesterone deserves particular attention. It rises steadily through pregnancy and is thought to play a major role in fibroid growth during this time. Some research suggests progesterone may promote cell division in fibroid tissue, though the exact mechanisms are still being studied.
Two other factors matter. First, blood volume increases substantially during pregnancy, and the uterus receives more blood flow. A fibroid with a richer blood supply has more resources available for growth. Second, the uterus itself expands dramatically to accommodate the growing fetus, and fibroids within the uterine wall are carried along with that expansion. Some of what appears to be fibroid growth is actually the surrounding tissue stretching and shifting.
It is worth being precise here: not all fibroids grow during pregnancy. Some stay the same size. A smaller number actually shrink. The response varies from woman to woman and even from fibroid to fibroid within the same uterus. Researchers have not identified exactly why some fibroids respond to pregnancy hormones with growth while others do not.
How Common Is Fibroid Growth During Pregnancy?
Fibroids are common in women of reproductive age, and they are found in a meaningful proportion of pregnancies. Research on how many fibroids grow during pregnancy has produced varied results. Some studies report that a majority of fibroids either grow or stay the same, while others find that many remain stable or shrink.
The variation in study findings is likely due to differences in how growth is measured, when during pregnancy measurements are taken, and the characteristics of the women studied. What is clear is that significant growth is a real possibility, not a rare event, and that it is most often observed in the first trimester.
Growth patterns also depend on the fibroid’s size and location. Larger fibroids and those located within the muscle wall of the uterus tend to be monitored more closely, though the relationship between size, location, and growth during pregnancy is not fully predictable.
Do Fibroids Shrink After Pregnancy?
Many do. After delivery, estrogen and progesterone levels drop sharply. Without the hormonal stimulation of pregnancy, fibroid tissue often decreases in size. This shrinkage typically happens over the weeks and months following childbirth.
Not every fibroid shrinks, and some may not return to their pre-pregnancy size. The degree of shrinkage varies. Some women find their fibroids are smaller than before pregnancy; others find they remain larger or unchanged. There is no reliable way to predict which way it will go for any individual fibroid.
Breastfeeding may influence this. Prolactin levels are high during breastfeeding, and estrogen levels tend to remain lower. Some clinicians suggest this hormonal environment may support continued fibroid shrinkage, though the evidence on this specific point is not strong enough to state as a certainty.
What Symptoms Can Growing Fibroids Cause During Pregnancy?
Many women with fibroids have no symptoms at all during pregnancy. When symptoms do occur, they tend to fall into a few categories.
- Pelvic pain or pressure, which can range from mild discomfort to more significant pain
- A feeling of fullness or heaviness in the lower abdomen
- Constipation or frequent urination, if a fibroid presses on nearby organs
- Back pain or leg discomfort in some cases
Pain is the most commonly reported symptom. It can be caused by a fibroid outgrowing its blood supply, a process sometimes called red degeneration. When a fibroid grows faster than its blood vessels can support, areas of the tissue can break down, causing pain that may be sharp and localized. This is more likely to occur in the second trimester and is usually managed with rest, hydration, and pain relief as directed by a clinician.
Some fibroids are associated with pregnancy complications, including an increased risk of preterm labor, breech presentation, and cesarean delivery. The relationship is not straightforward, and many women with fibroids have uncomplicated pregnancies. The size, number, and location of fibroids all appear to play a role, but predicting outcomes for an individual pregnancy remains difficult.
How Are Fibroids Monitored During Pregnancy?
Fibroids are usually monitored with ultrasound. If a fibroid was identified before pregnancy, or if one is found during a routine scan, a clinician may recommend periodic imaging to track any changes in size.
Monitoring is generally more about watching for symptoms and complications than about treating the fibroid itself. Most fibroids are not treated during pregnancy unless they are causing significant problems. Surgery to remove fibroids during pregnancy is uncommon and carries risks, so it is typically reserved for serious situations.
If pain becomes difficult to manage or if other complications arise, a care team may adjust the monitoring approach. The goal is to support the pregnancy while keeping an eye on any fibroid-related issues.
What Does Not Cause Fibroids To Grow During Pregnancy?
Several common beliefs about fibroid growth do not hold up. Fibroids are not caused by caffeine, stress, or a woman’s diet during pregnancy, though these factors can affect general health. They are not the result of something the mother did or did not do.
Fibroids are also not cancer. They are benign tumors of the uterus, and while they can cause symptoms and complications, they do not become malignant. This distinction matters because the word “tumor” can be alarming. Uterine fibroids are not associated with an increased risk of uterine cancer.
It is also not accurate to say that pregnancy always makes fibroids grow. The response is variable. Some grow, some stay the same, and some shrink. The hormonal environment creates the conditions for growth, but it does not guarantee it.
What Should You Do If You Have Fibroids and Are Pregnant?
Tell your care team. If you know you have fibroids, make sure your obstetric provider is aware. This allows them to monitor appropriately and to be alert to any symptoms that might need attention.
Report new or worsening symptoms. Pelvic pain, especially if it is severe or accompanied by fever, should be evaluated. While most fibroid-related pain is manageable, it is important to rule out other causes.
Follow your provider’s monitoring plan. If they recommend additional ultrasounds, keep those appointments. The information helps guide care if complications arise.
There is no diet, supplement, or lifestyle change proven to prevent fibroid growth during pregnancy. Be cautious of any product or program that claims otherwise. The evidence does not support those claims.
Frequently Asked Questions
Do fibroids always grow during pregnancy?
No. Some fibroids grow, some stay the same size, and some shrink during pregnancy. The response varies from woman to woman and even among different fibroids in the same uterus.
Can fibroids cause a miscarriage?
Some research suggests fibroids may be associated with a slightly increased risk of miscarriage, but the evidence is mixed and the relationship is not fully understood. Many women with fibroids have healthy pregnancies.
Will my fibroids go back to normal after delivery?
Many fibroids shrink after delivery as hormone levels drop, but not all do. Some may remain larger than they were before pregnancy.
Is it safe to get pregnant with fibroids?
Most women with fibroids can have healthy pregnancies, though fibroids may increase the risk of certain complications. Your provider can assess your individual situation and recommend appropriate monitoring.
