A diagnosis of a two-vessel umbilical cord, known medically as a Single Umbilical Artery (SUA), is understandably concerning for expectant parents. The most reassuring fact is that the vast majority of babies survive and thrive despite this finding. For many, the single artery is an isolated anatomical variation that does not impact the baby’s health or long-term development. This anomaly is defined by the cord containing only one artery and one vein, instead of the typical two arteries and one vein. However, the presence of SUA prompts healthcare providers to perform a detailed evaluation of the fetus.
Understanding the Single Umbilical Artery
The umbilical cord is the lifeline connecting the fetus to the placenta, normally composed of three vessels: two small arteries and one larger vein. The vein carries oxygen-rich blood and nutrients to the baby, while the two arteries transport deoxygenated blood and waste products back to the placenta. SUA occurs when one of these two arteries is absent, resulting in a two-vessel cord.
This finding is the most common abnormality of the umbilical cord, occurring in approximately 0.5% to 1% of all singleton pregnancies. The precise cause of why one artery fails to develop or atrophies during the early stages of pregnancy is largely unknown. It is important for parents to understand that this anomaly is typically not linked to any specific actions or lack of action on their part.
Diagnosis is most often made during the mid-pregnancy anatomy ultrasound scan, usually between 18 and 22 weeks of gestation. The sonographer can visualize the vessels in a cross-section of the cord or by using color Doppler imaging. While the finding itself does not cause direct harm, its detection serves as a marker that prompts a comprehensive medical assessment.
Potential Associated Health Concerns
While many babies with SUA are perfectly healthy, the primary concern is that it can sometimes be a sign of other congenital anomalies. Approximately 65% to 80% of SUA cases are considered “isolated,” meaning no other structural or chromosomal issues are found during prenatal evaluation. In isolated cases, the prognosis is generally positive and similar to pregnancies with a normal three-vessel cord.
The remaining cases are classified as “non-isolated SUA” because they are accompanied by other findings, which significantly influence management and outcome. The most common associated anomalies involve the renal and cardiovascular systems.
Genitourinary malformations, such as kidney agenesis or hydronephrosis, occur in about 7% to 9% of infants with isolated SUA, with higher rates seen in non-isolated cases. Cardiovascular issues, including various congenital heart defects, are also frequently associated with non-isolated SUA, sometimes occurring 7 to 8 times more often than in the general population.
A non-isolated SUA also increases the likelihood of chromosomal abnormalities, with Trisomy 18 and Trisomy 13 being the most common. These co-existing conditions, not the single artery itself, necessitate increased monitoring and are responsible for the reported increase in perinatal mortality associated with SUA.
Prenatal Monitoring and Clinical Management
Once SUA is identified, clinical management focuses on ruling out associated anomalies and ensuring appropriate fetal growth. The first step involves a comprehensive, detailed ultrasound, often performed by a maternal-fetal medicine specialist, to thoroughly examine the baby’s anatomy. This scan pays particular attention to the kidneys, heart, and central nervous system, as these are the most common sites for co-existing issues.
A fetal echocardiogram, a specialized ultrasound of the heart, is often recommended to meticulously assess the heart’s structure and function. If any additional structural anomalies are detected, genetic testing such as amniocentesis or chromosomal microarray may be offered to check for aneuploidy.
Increased monitoring for fetal growth is a standard component of management, even for isolated SUA, due to a slightly elevated risk of Fetal Growth Restriction (FGR). Serial growth ultrasounds are typically started in the late second or early third trimester, often around 28 to 32 weeks, and repeated frequently. These scans measure the baby’s size and use Doppler flow studies to evaluate blood flow efficiency in the umbilical and cerebral arteries. Monitoring helps identify growth concerns early, allowing for timely intervention.
Delivery and Long-Term Outlook
The diagnosis of an isolated SUA generally does not change the planned mode of delivery. A vaginal birth remains a safe option; a cesarean section is typically only necessary if other obstetric complications, such as severe Fetal Growth Restriction, arise. The delivery team will examine the umbilical cord after birth to confirm the presence of only two vessels.
After birth, the baby undergoes a thorough physical examination by a pediatrician. Further testing may be performed based on prenatal findings. Because of the association with genitourinary issues, a postnatal renal ultrasound is often recommended to confirm the presence and structure of both kidneys, especially if prenatal images were inconclusive.
The long-term prognosis for children born with an isolated SUA is excellent. Studies comparing children with an isolated SUA to those with a normal cord have found no significant differences in physical growth or neurodevelopmental outcomes up to seven years of age. For the majority of babies, the two-vessel cord proves to be a benign anatomical variation that necessitates careful prenatal screening.