A diagnosis of a two-vessel umbilical cord, also known as a Single Umbilical Artery (SUA), can cause significant concern for expectant parents. The majority of babies with this condition will survive and thrive. The umbilical cord serves as a life support connection, carrying oxygen and nutrients to the baby and removing waste products. This variation in cord anatomy occurs in approximately 1% of singleton pregnancies. While SUA increases the potential for other health concerns, in many instances, it is an isolated finding, leading to a healthy baby.
Understanding the Single Umbilical Artery
A typical umbilical cord is known as a three-vessel cord because it contains two arteries and one vein. The single vein carries oxygenated blood and nutrients from the placenta to the fetus. The two arteries carry deoxygenated blood and metabolic waste products away from the fetus back to the placenta.
A two-vessel cord is characterized by the absence of one artery, resulting in only one artery and one vein. Scientists believe this difference results from the failure of one artery to develop or the atrophy of a previously formed artery early in pregnancy. The single remaining artery frequently compensates for the missing vessel by enlarging its diameter to manage the entire blood flow.
Detection and Prenatal Monitoring Protocols
A Single Umbilical Artery is typically discovered during the second-trimester anatomy scan, a detailed ultrasound performed around 18 to 20 weeks of gestation. The sonographer identifies the two-vessel cord by counting the vessels in a cross-section or by observing the single artery using color Doppler imaging. Once an SUA is identified, it triggers specialized monitoring for the remainder of the pregnancy.
Initial management focuses on a comprehensive check for other structural differences, as SUA can be a marker for them. This involves a detailed review of the fetal heart and kidneys, the most common areas of associated concern. A fetal echocardiogram, a specialized ultrasound of the baby’s heart, may be recommended to rule out any subtle cardiac anomalies.
If no other issues are found, the condition is referred to as an isolated Single Umbilical Artery. Monitoring continues with increased frequency of growth scans in the third trimester. These serial ultrasounds are performed to monitor for Fetal Growth Restriction (FGR) or a baby being born Small for Gestational Age (SGA), which is a slightly increased risk with SUA. This close observation ensures that the fetus is receiving adequate nutrition and oxygen.
Associated Health Concerns and Prognosis
The prognosis for a baby with a two-vessel cord depends on whether the finding is isolated or non-isolated. In cases of isolated SUA, where no other fetal anomalies are detected after a thorough ultrasound evaluation, the outlook is positive. The majority of these babies are born healthy, and isolated SUA is often considered a normal developmental variation. Although there is a slightly elevated risk for preterm birth or lower birth weight, the baby is generally expected to be healthy.
More careful consideration is required when the SUA is non-isolated, meaning it is accompanied by other structural differences. Such associations occur in approximately 20% to 30% of cases. The most common systems implicated are the renal, cardiac, and gastrointestinal systems.
Renal (kidney) anomalies are the most frequent association, occurring in a significant percentage of non-isolated cases. These can range from minor issues like vesicoureteric reflux to more serious structural differences of the kidneys or urinary tract. Cardiac (heart) anomalies also require careful screening, as they can significantly affect the baby’s health. Less common are skeletal and gastrointestinal issues. Survival and long-term health in non-isolated cases are tied directly to the severity of these associated structural differences.
Delivery and Postnatal Evaluation
The presence of a Single Umbilical Artery alone does not dictate the method of delivery. Unless there are complications like severe fetal growth restriction or other obstetric concerns, a vaginal delivery is appropriate. Continuous monitoring of the baby’s heart rate remains the focus during labor, which is standard practice.
Immediately following birth, the pediatrician performs a thorough physical examination to check for associated anomalies. Due to the strong link between SUA and renal issues, an ultrasound of the kidneys and urinary tract is often ordered shortly after birth. If the baby passes these checks with no apparent structural differences, no further long-term monitoring related to the two-vessel cord is required.