Management of Isolated Single Umbilical Artery at 18 Weeks
For this 28-year-old pregnant woman at 18 weeks with an isolated single umbilical artery and no other congenital anomalies, the recommended management is routine antenatal care with enhanced third-trimester surveillance—no genetic counseling, no fetal echocardiography, and absolutely no termination of pregnancy is indicated. 1, 2
Immediate Management: No Additional Testing Required
No genetic counseling or aneuploidy testing is needed because isolated single umbilical artery shows no increased risk of aneuploidy, regardless of whether previous screening was performed or declined. 1, 2, 3
The Society for Maternal-Fetal Medicine explicitly states that diagnostic testing for aneuploidy is not recommended solely for an isolated soft marker following negative screening. 2
Even if no prior aneuploidy screening was done, the American College of Obstetricians and Gynecologists recommends no additional evaluation for aneuploidy when single umbilical artery is truly isolated. 2, 3
Cardiac Evaluation: Already Complete
Fetal echocardiography is NOT routinely warranted if the comprehensive cardiac assessment on the anatomy scan was adequate and normal. 2, 3
While cardiovascular anomalies are strongly associated with single umbilical artery (odds ratios 5.9-20.3), the key is that a comprehensive assessment of cardiac anatomy should already have been performed during the anomaly scan. 2, 4
If the required cardiac views were adequately visualized and normal during the 18-week scan, no additional cardiac imaging is needed. 3
Required Third-Trimester Surveillance Protocol
The critical management step is enhanced surveillance in the third trimester:
Schedule a third-trimester ultrasound examination at 32-36 weeks to evaluate fetal growth, as neonates with isolated single umbilical artery have increased rates of growth restriction. 1, 2, 3
Plan for weekly antenatal fetal surveillance beginning at 36 0/7 weeks of gestation due to increased risks of stillbirth (nearly 5-fold increased risk with OR 4.80), polyhydramnios, oligohydramnios, placental abruption, cord prolapse, and perinatal mortality. 1, 2, 3, 4
Research confirms that isolated single umbilical artery is associated with increased rates of prematurity, growth restriction, and adverse neonatal outcomes, justifying this enhanced surveillance. 5
Postnatal Notification
- Notify the pediatric provider at delivery of the prenatal findings, as postnatal examination revealed structural anomalies in up to 7% of infants with prenatal diagnosis of isolated single umbilical artery. 2, 3
Common Pitfalls to Avoid
Do not offer termination of pregnancy—this is completely inappropriate for an isolated finding with no structural or chromosomal abnormalities. 1, 2
Do not order unnecessary genetic testing—this wastes resources and causes unnecessary anxiety when isolated single umbilical artery carries no increased aneuploidy risk. 1, 2
Do not skip the third-trimester growth scan—this is the most important intervention, as growth restriction occurs in approximately 8% of isolated cases and requires different delivery timing. 3, 5, 6
Ensure the anatomy scan truly showed "no congenital anomaly"—research shows that when single umbilical artery appears isolated on ultrasound, major structural defects are occasionally missed, particularly renal anomalies (16% of isolated cases) and cardiovascular defects. 4, 6