Many women are concerned about the impact of uterine fibroids during pregnancy, particularly regarding the risk of second-trimester miscarriage. This article clarifies their relationship with pregnancy outcomes, including potential complications and management.
Understanding Uterine Fibroids
Uterine fibroids, also known as leiomyomas, are growths composed of muscle and connective tissue that form within the uterine wall or on its surface. They are typically benign and the most common non-cancerous tumors found in women. Fibroids can vary significantly in size, from microscopic to large masses.
They are categorized by their location. Intramural fibroids develop within the muscular wall and are the most common type. Subserosal fibroids grow on the outer surface, sometimes attached by a stalk (pedunculated). Submucosal fibroids are less common but grow just beneath the uterine lining, protruding into the uterine cavity. Fibroids are prevalent, affecting an estimated 20% to 80% of women by the age of 50.
Fibroids and Second Trimester Miscarriage
While common, uterine fibroids are infrequently directly associated with second-trimester miscarriage. However, certain characteristics can increase this risk. Most women with fibroids have uncomplicated pregnancies, but fibroids can elevate the rate of spontaneous miscarriage. Women with fibroids may have a miscarriage rate of approximately 14% compared to about 7.6% in those without fibroids.
Several factors allow fibroids to contribute to second-trimester miscarriage. Submucosal fibroids, especially those bulging into the uterine cavity, can distort the uterus, potentially affecting fetal growth or placental implantation. This distortion can also impair blood supply to the placenta or fetus, as fibroids may compete for uterine blood flow.
Additionally, fibroid degeneration, common in the second or third trimester when the fibroid outgrows its blood supply, can cause severe pain and inflammation. This may trigger uterine contractions or placental issues leading to miscarriage. The risk of second-trimester miscarriage is higher with large or multiple fibroids, especially if located within the uterine cavity.
Other Pregnancy Complications Linked to Fibroids
Beyond second-trimester miscarriage, uterine fibroids can be associated with several other pregnancy complications. These include an increased risk of preterm labor and delivery (before 37 weeks of gestation). This can occur due to uterine contractions from fibroid-related pain or inflammation, or because the fibroid affects the uterus’s ability to stretch and maintain pregnancy.
Fibroids may also lead to placental complications, such as placental abruption (where the placenta detaches prematurely) or placenta previa (where the placenta covers part or all of the cervix). Fibroid location, particularly near the placental implantation site, can increase the likelihood of these conditions, compromising the baby’s oxygen and nutrient supply.
Furthermore, fibroids can distort the uterine cavity, potentially causing fetal malpresentation, such as a breech or transverse lie, making vaginal delivery more challenging. This often necessitates a cesarean section (C-section), as women with fibroids are more likely to require one. Large fibroids, or those in the lower uterine segment, can obstruct the birth canal, impeding vaginal birth. Another potential complication is postpartum hemorrhage, a risk that increases with larger fibroid size and specific locations, due to impaired uterine contraction after delivery.
Managing Fibroids While Pregnant
Managing uterine fibroids during pregnancy focuses on monitoring and addressing symptoms. Regular ultrasounds track fibroid size, location, and potential impact on fetal development. This monitoring helps anticipate complications.
For pain or discomfort, including from fibroid degeneration, conservative approaches are preferred. Rest, hydration, and over-the-counter pain relievers like acetaminophen are recommended. Nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen are generally avoided later in pregnancy due to potential risks to the fetus.
Surgical removal of fibroids (myomectomy) during pregnancy is generally not recommended due to increased bleeding and other complications, including miscarriage. However, in very rare cases of intractable pain or if a fibroid obstructs the birth canal, myomectomy might be considered. Delivery planning is influenced by fibroids; while vaginal birth is often possible, their size and location may necessitate a C-section. Most women with fibroids experience uncomplicated pregnancies and deliver healthy babies.