Uterine fibroids (leiomyomas or myomas) are non-cancerous growths originating from the muscle tissue of the uterus. They are common, affecting 50% to 80% of women by age 50, though many remain unaware they have them because they cause no symptoms. These growths are hormonally sensitive. Their presence during pregnancy raises concerns about how the surge of hormones might affect fibroid size and whether they pose risks to the mother or the developing baby.
The Direct Answer: Fibroid Growth Patterns
Fibroid growth depends highly on the reproductive hormones estrogen and progesterone, which are abundant throughout pregnancy. These tumors have a higher density of receptors for both hormones compared to normal uterine tissue, making them responsive to the hormonal surge. Growth is most likely to occur during the first trimester. The rapid rise in hormones fuels cell division and enlargement, causing up to one-third of fibroids to increase in volume.
The change in size is not universal; a majority of fibroids remain stable or show no significant growth throughout pregnancy. After the first trimester, growth often stabilizes or may slightly reduce in size during the second and third trimesters. The ultimate size change is also influenced by the fibroid’s classification, such as intramural, subserosal, or submucosal. Furthermore, rapid growth can sometimes outpace the blood supply’s ability to nourish the tissue, leading to degeneration.
Risks to Mother and Baby During Pregnancy
Fibroids can introduce several complications before labor, though most women still have a successful pregnancy. A primary maternal concern is acute pain, often caused by “red degeneration” or necrobiosis. This occurs when the fibroid outgrows its blood supply, causing tissue breakdown and severe localized abdominal discomfort, typically in the second and third trimesters.
The fibroid’s location significantly affects the risk profile, especially if positioned near the placenta. Submucosal fibroids, which bulge into the uterine cavity, increase the risk of spontaneous miscarriage. Larger fibroids (over five centimeters) are associated with a higher likelihood of complications, including preterm birth and placental abruption. Large fibroids can also restrict fetal growth or lead to fetal malpresentation by limiting space within the uterus.
Influence on Labor and Delivery
Fibroids, especially large ones or those in the lower uterine segment, can directly affect labor and delivery. A major concern is the increased likelihood of a cesarean section (C-section). This surgical delivery is often necessary if a fibroid physically blocks the birth canal or causes the baby to be in an abnormal position, such as breech.
Fibroids can also interfere with the uterus’s ability to contract effectively, known as uterine dysfunction, leading to prolonged labor. The risk of postpartum hemorrhage (PPH) is elevated because fibroids can impede the uterus from clamping down properly after delivery. This failure to contract, known as uterine atony, is a common cause of excessive bleeding.
Monitoring and Management During Gestation
Management of fibroids during pregnancy is generally expectant, involving careful monitoring without active intervention unless complications arise. Regular ultrasound surveillance tracks the size and location of fibroids, assesses fetal growth, and monitors placental health. This tracking helps the healthcare team anticipate potential problems and plan the safest method of delivery.
When a patient experiences pain, treatment focuses on conservative measures like bed rest, increased hydration, and simple analgesics such as acetaminophen. Surgical removal (myomectomy) is strongly discouraged during pregnancy due to the high risk of hemorrhage, miscarriage, or preterm labor. Myomectomy is only considered in exceedingly rare cases where pain is severe and unresponsive to conservative treatment.