Uterine fibroids (leiomyomas) are common, non-cancerous growths that develop in or on the muscular wall of the uterus. Many women are unaware they have them until pregnancy, as gestation alters the hormonal environment and blood flow, which can influence these growths. Understanding how fibroids interact with a developing pregnancy is important for expectant mothers and care providers.
Changes in Fibroid Size During Gestation
Fibroid behavior during pregnancy is highly variable. While many fibroids remain stable in size throughout gestation, studies show that about one-third will increase in volume. This growth is most common during the first trimester, coinciding with peak hormonal activity. After the first trimester, the trend often shifts toward stability or even shrinkage.
The size of the fibroid at the start of pregnancy is a factor in its growth trajectory. Smaller fibroids (less than one centimeter) are more likely to increase in size than large fibroids. Conversely, large fibroids (greater than three centimeters) tend to decrease in volume or remain unchanged.
Factors Driving Fibroid Change
The primary drivers of change in fibroid size are the elevated levels of reproductive hormones that accompany pregnancy. Both estrogen and progesterone are present in high concentrations and have a direct effect on fibroid tissue. Estrogen stimulates the proliferation and growth of fibroid cells, leading to potential enlargement.
Progesterone also plays a role by promoting cell survival and inhibiting the natural process of cell death within the fibroid. Furthermore, the dramatic increase in blood flow to the uterus, known as hyperemia, provides fibroids with more nutrients and oxygen. This combination of hormonal stimulation and increased vascular supply contributes to the enlargement observed in early pregnancy.
Potential Complications During Pregnancy
While most women with fibroids have uncomplicated pregnancies, their presence can introduce specific risks that require careful monitoring. The most common complication is acute pain, frequently caused by a condition called red degeneration. This occurs when a fibroid outgrows its blood supply, leading to cell death and inflammation, which often presents as severe abdominal pain in the second and third trimesters.
Fibroids can also increase the risk of adverse outcomes related to the placement and growth of the fetus. Submucosal fibroids, or those located near the placenta, are associated with a higher risk of early pregnancy loss, or miscarriage. Later in gestation, fibroids increase the likelihood of preterm labor and delivery, placental abruption, and fetal malpresentation (such as a breech position). During childbirth, large fibroids can block the birth canal, leading to a significantly increased chance of needing a Cesarean section.
Monitoring and Symptom Management
The management of fibroids during pregnancy is primarily focused on monitoring their size and location with routine ultrasounds and addressing any symptoms that arise. For pregnant women experiencing pain, the treatment approach is conservative and aims to alleviate discomfort without harming the fetus. This typically involves rest, maintaining adequate hydration, and the use of appropriate analgesic medications.
In cases of severe pain from red degeneration, non-steroidal anti-inflammatory drugs (NSAIDs) may be used for a short duration, but must be avoided later in pregnancy (after 32 weeks) due to potential fetal side effects. Surgical removal of fibroids (myomectomy) is almost never performed during pregnancy because of the high risk of hemorrhage and pregnancy loss. Following delivery, fibroids typically regress in size, with many women experiencing a significant reduction in volume within the first few months postpartum.