Uterine fibroids are common, non-cancerous growths found in the muscular wall of the uterus, and their presence during gestation is a frequent concern. While many women with fibroids experience entirely normal pregnancies, the growths can sometimes contribute to complications, including bleeding. Bleeding in pregnancy, particularly in the first trimester, is relatively common, but fibroids can be a factor that increases this risk. Understanding how these growths interact with the developing pregnancy is important for proper clinical monitoring.
Understanding Uterine Fibroids
Uterine fibroids, also known as leiomyomas or myomas, are benign tumors composed of smooth muscle cells and fibrous connective tissue. They are common, affecting a large percentage of women, and are often discovered incidentally during prenatal ultrasound examinations. The prevalence of fibroids found during pregnancy is reported to range between approximately 1.6% and 10.7%.
Fibroids are classified based on their location within the uterine wall, which influences the likelihood of symptoms and complications. Submucosal fibroids project into the uterine cavity, intramural fibroids are embedded within the muscular wall, and subserosal fibroids bulge from the outer surface of the uterus. Because fibroids are sensitive to hormones, particularly estrogen, the hormonal surge of pregnancy can sometimes cause them to grow, especially in the first trimester. However, many fibroids do not change size during gestation, and some may decrease in volume later in pregnancy.
Mechanisms of Fibroid-Related Bleeding
Fibroids can cause bleeding during pregnancy through mechanisms related to their size, location, and interaction with the pregnancy environment. One major cause of pain and sometimes bleeding is red degeneration (necrobiosis). This occurs when the rapidly growing fibroid outgrows its blood supply, causing tissue death, localized pain, and inflammation.
A fibroid’s location near the placenta or uterine lining can directly interfere with pregnancy attachment. If a fibroid is submucosal or close to the inner lining, it can disrupt the decidua, the specialized tissue lining the uterus during pregnancy. This disruption can lead to localized inflammation or separation, manifesting as vaginal bleeding.
Bleeding risk is especially elevated if the placenta implants near or directly over a fibroid. When the placenta is positioned adjacent to a fibroid, the rate of bleeding in early pregnancy is significantly higher. This proximity can compromise the blood flow or stability of the placental attachment, contributing to early pregnancy loss or marginal bleeding.
Other Pregnancy Risks Associated with Fibroids
Beyond bleeding, uterine fibroids are associated with several other potential complications during pregnancy and delivery. Large or multiple fibroids can act as irritants to the uterus, leading to increased uterine contractility and a higher chance of preterm labor and delivery. Women with fibroids are statistically more likely to deliver their baby before 37 weeks of gestation.
Fibroids can also mechanically obstruct the fetus’s ability to settle into the proper position for birth. Growths in the lower segment of the uterus can physically block the birth canal or prevent the baby from turning head-down, increasing the likelihood of breech or other fetal malpresentation. This obstruction is a primary reason fibroids are linked to a higher rate of Cesarean delivery.
In the delivery period, fibroids can interfere with the uterus’s ability to contract effectively after birth. This reduced contractility, known as uterine atony, increases the risk of postpartum hemorrhage (excessive bleeding after delivery). Fibroids can also be associated with a higher risk of placental abruption, a serious condition where the placenta prematurely separates from the uterine wall.
Monitoring and Clinical Management
When fibroids are identified during pregnancy, a conservative, watchful approach is employed. Routine monitoring through ultrasound tracks the size and location of the fibroids and ensures they are not interfering with fetal growth or positioning. This imaging helps the clinical team anticipate potential delivery complications.
Management of pain, often resulting from red degeneration, focuses on conservative measures such as rest, hydration, and appropriate pain relief. Acetaminophen is used for mild to moderate discomfort. NSAIDs may be used briefly for severe pain, but their use is limited later in pregnancy due to fetal risks. Surgical removal of fibroids (myomectomy) is rarely performed during pregnancy due to the high risk of hemorrhage and pregnancy loss, and is reserved for extremely rare, severe cases. Patients should report any severe pain, heavy bleeding, or signs of preterm labor to their healthcare provider immediately.