Uterine fibroids, also known as leiomyomas or myomas, are common, non-cancerous growths composed of muscle cells that develop within the wall of the uterus. These growths are detected in an estimated 3% to 12% of pregnant women, though the true prevalence may be higher since many fibroids cause no symptoms. While fibroids can introduce complexities, the majority of women who have them experience full-term, healthy pregnancies. Understanding how pregnancy alters these growths and the specific risks they may pose to both mother and baby is important.
How Pregnancy Affects Fibroids
The hormonal environment of pregnancy significantly influences the size and activity of fibroids. High levels of estrogen and progesterone circulating during gestation can stimulate fibroid growth, with approximately one-third of fibroids increasing in volume. This growth is most commonly observed during the first trimester, after which the fibroids typically stabilize or may even decrease in size.
Acute pain caused by red degeneration, or ischemic degeneration, is a significant complication associated with fibroids during pregnancy. This occurs when the fibroid grows so rapidly that it outstrips its blood supply from the uterus. The resulting lack of oxygen causes the tissue within the fibroid to break down, triggering inflammation and the release of prostaglandins.
Red degeneration is most common during the second trimester and can manifest as severe, localized abdominal pain, often accompanied by tenderness, a low-grade fever, nausea, or vomiting. Fibroids larger than five centimeters are more prone to this condition due to their increased nutritional demands. While painful, this degenerative process is usually self-limiting and rarely poses a direct threat to the pregnancy.
Risks to the Mother and Pregnancy Outcome
The potential risks associated with fibroids largely depend on their size, number, and location within the uterus. In early pregnancy, the presence of fibroids, particularly those that distort the uterine cavity, can double the risk of spontaneous miscarriage compared to women without fibroids. Bleeding in the first trimester is also significantly more common when the placenta implants near a fibroid.
Fibroids can increase the likelihood of preterm delivery (birth before 37 weeks of gestation). Women with fibroids have an elevated rate of preterm birth, particularly when fibroids are multiple or positioned close to the placenta. The pain and inflammation from red degeneration can sometimes trigger uterine contractions, potentially leading to threatened preterm labor.
Placental complications are a concern, including placental abruption, where the placenta prematurely separates from the uterine wall. Fibroids situated directly behind the placenta may interfere with its blood flow or attachment, although this complication remains rare. Large fibroids can also limit the space available for the fetus, potentially leading to fetal growth restriction and lower birth weight.
Fetal positioning can be affected, with an increased incidence of malpresentation, such as breech position. If a fibroid is located in the lower segment of the uterus, it may obstruct the birth canal, a condition known as labor dystocia. This obstruction, or the presence of large fibroids, contributes to a much higher rate of Cesarean section for delivery.
Following delivery, women with large or multiple fibroids face an elevated risk of postpartum hemorrhage. This increased bleeding is thought to be due to the fibroids interfering with the uterus’s ability to contract effectively, which is necessary to clamp down on blood vessels. Close monitoring and proactive management of the third stage of labor are often required.
Monitoring and Treatment During Pregnancy
Management of fibroids during pregnancy is primarily conservative, focusing on minimizing symptoms and monitoring fibroid growth. Regular prenatal ultrasounds track the size and location of the fibroids and assess their relationship to the placenta. This monitoring helps the healthcare team anticipate potential complications as the pregnancy progresses.
For managing the pain associated with fibroid degeneration, the first-line treatment involves rest and ensuring adequate hydration. Acetaminophen is the preferred pain medication because it is considered safe throughout all trimesters of pregnancy. Nonsteroidal anti-inflammatory drugs (NSAIDs) may be used cautiously, but their use is generally avoided after 32 weeks of gestation due to potential fetal risks.
Surgical removal of fibroids (myomectomy) is generally avoided during pregnancy due to the high risk of bleeding and potential for miscarriage or preterm labor. Surgery is reserved for extremely rare circumstances when pain is intractable or if a complication like fibroid torsion occurs. Most fibroids that cause no symptoms require no specific intervention.