Uterine fibroids are common, noncancerous growths of the uterus, so their discovery during a pregnancy ultrasound is not unusual. While many individuals with fibroids have uneventful pregnancies, these growths can sometimes influence the course of pregnancy and delivery. Understanding how they are monitored and what effects they might have is important for expectant parents.
The Role of Ultrasound in Diagnosis and Monitoring
Ultrasound is the primary imaging tool to evaluate fibroids during pregnancy because it poses no risk to the fetus. This technique provides detailed images of the uterus, allowing a sonographer or physician to gather specific information. A combination of transabdominal and transvaginal ultrasounds is often used for a comprehensive view. The transvaginal approach offers higher resolution, while the transabdominal scan provides a broader overview of the uterus.
During the scan, a focus is identifying the fibroid’s location, which is classified by its position within the uterine wall. Submucosal fibroids are located just under the uterine lining, intramural fibroids are within the muscular wall of the uterus, and subserosal fibroids grow on the outer surface. The location is a factor because fibroids near the uterine lining may have a greater impact on the pregnancy.
Clinicians also use the ultrasound to measure the size and count the number of fibroids present. Another assessment is the fibroid’s proximity to other structures, particularly the placenta and the cervix. A fibroid located behind the placenta or near the cervix could influence decisions regarding the delivery plan.
How Pregnancy Affects Fibroids
The hormonal environment of pregnancy, with elevated estrogen levels, can influence fibroid behavior. This can lead to an increase in fibroid size, with most growth occurring in the first trimester. Studies show that while 22% to 32% of fibroids increase in volume, the majority (60% to 78%) do not change size significantly. In some cases, fibroids may even decrease in size.
A specific concern with rapidly growing fibroids is “red degeneration.” This occurs when a fibroid outgrows its blood supply, leading to tissue death and causing localized abdominal pain. This complication is most often seen with large fibroids, typically those greater than 5 centimeters, and tends to occur during the second and third trimesters. The pain is usually manageable with treatments like rest and hydration.
Potential Impact of Fibroids on Pregnancy and Delivery
While most women with uterine fibroids experience healthy pregnancies, the growths can increase the likelihood of certain complications. The specific risks are often related to the fibroid’s size and location. Pain is the most common complication, frequently linked to the degeneration of large fibroids.
The location of fibroids can influence the pregnancy from its earliest stages. Fibroids that distort the uterine cavity are associated with a higher rate of spontaneous miscarriage. As the pregnancy progresses, a fibroid located behind the placenta may increase the risk of placental abruption, where the placenta separates from the uterine wall. Fibroids can also affect fetal growth or lead to preterm labor.
Toward the end of pregnancy, fibroids can affect the baby’s position in the uterus. They may block the baby from settling into the head-down presentation, resulting in a breech position. This situation increases the chance that a Cesarean section will be needed. There is also an association between fibroids and a greater risk of postpartum hemorrhage, which is excessive bleeding after delivery.
Altered Ultrasound Schedules and Management
The presence of significant fibroids typically prompts a more frequent ultrasound schedule than a low-risk pregnancy. This enhanced monitoring allows the healthcare team to track changes in the fibroids and keep a close eye on the baby’s development. These additional scans help in the early detection of any potential issues.
This modified schedule often includes regular growth scans, particularly during the third trimester. These ultrasounds are used to monitor the fibroid’s size and to ensure the baby is growing at a healthy rate. The information gathered guides the management of the pregnancy and helps in making informed decisions about delivery.
The findings from these ultrasounds play a direct role in planning for the birth. For example, if a large fibroid is located in the lower part of the uterus, it might obstruct the birth canal, making a planned Cesarean section the safest option. This increased surveillance helps anticipate and prepare for any challenges.