Uterine fibroids are non-cancerous growths composed of muscle and tissue that develop in or on the uterus. They can vary in size from microscopic to as large as a grapefruit. While many women have fibroids without experiencing any symptoms, the presence of fibroids during pregnancy can sometimes lead to concerns, including vaginal bleeding.
Fibroids During Pregnancy
Uterine fibroids are common, affecting an estimated 40% to 60% of women by age 35 and up to 80% by age 50. These benign growths can be located in various places: within the uterine wall (intramural), just under the uterine lining (submucosal), or on the outer surface of the uterus (subserosal). Many women with fibroids will experience a typical pregnancy without complications.
Pregnancy hormones, particularly estrogen and progesterone, can influence fibroid size. About one-third of uterine fibroids may increase in size during the first trimester when hormone levels are highest. However, most fibroids typically do not change in size during pregnancy, and some may even shrink spontaneously after delivery as the uterus returns to its normal size.
How Fibroids Lead to Bleeding
Fibroids can cause bleeding during pregnancy through several mechanisms. One common cause is “red degeneration,” which occurs when a fibroid outgrows its blood supply, leading to tissue death and necrosis. This process can result in severe pain and vaginal bleeding. Red degeneration is more frequently observed in larger fibroids, typically those over 5 cm.
Fibroids, especially those located near the uterine lining or within the uterine cavity, can interfere with the implantation and development of the placenta. If the placenta implants close to a fibroid, it can increase the risk of bleeding due to a subchorionic hematoma, a collection of blood between the uterine wall and chorionic membrane. While often not serious, a subchorionic hematoma can cause vaginal bleeding in the first half of pregnancy. In rare instances, a large fibroid positioned behind the placenta may increase the risk of placental abruption, a serious condition of premature placental separation. This separation can lead to significant bleeding and compromise the baby’s oxygen supply.
Other Effects of Fibroids on Pregnancy
Beyond bleeding, fibroids can lead to other complications during pregnancy. Pain is a frequent symptom, particularly with larger fibroids, and can be severe enough to require hospitalization. This pain may stem from the fibroid outgrowing its blood supply or from the fibroid pressing on other internal organs as the uterus expands.
Fibroids can also increase the risk of preterm labor (before 37 weeks). This may be due to uterine irritability or contractions induced by the fibroid’s presence. Fetal malpresentation, such as breech position, can occur if fibroids obstruct the birth canal or restrict the baby’s movement within the uterus. The presence of fibroids also increases the likelihood of needing a cesarean section, with women being six times more likely to require one compared to those without fibroids.
When to Contact Your Doctor
Any vaginal bleeding during pregnancy should prompt immediate contact with a healthcare provider. While some bleeding may be minor, it is important to rule out more serious causes. Seek medical attention for heavy bleeding, severe or persistent pelvic pain, fever, or chills.
Ongoing tiredness and weakness, which can indicate anemia from blood loss, also warrant medical consultation. A healthcare provider can assess the situation, determine the cause of the bleeding or other symptoms, and recommend appropriate management.