Management of Isolated Single Umbilical Artery at 18 Weeks
For a pregnant woman at 18 weeks with an isolated single umbilical artery and no congenital anomalies on the anomaly scan, the answer is B (ECHO) if cardiac anatomy was not comprehensively assessed, but if the anatomy scan already included detailed cardiac evaluation, then proceed with C (Routine Antenatal care with enhanced surveillance). 1
Immediate Cardiac Assessment
A comprehensive assessment of cardiac anatomy should be performed immediately, as cardiovascular anomalies are the most commonly affected systems when single umbilical artery occurs with structural abnormalities, with odds ratios ranging from 5.9 to 20.3 for various cardiac defects. 1, 2
If the anatomy scan already included a comprehensive cardiac assessment and it was normal, fetal echocardiography is not routinely warranted. 1
Renal system evaluation is also critical, as renal anomalies show a 3-fold increased risk, with approximately 16% of isolated single umbilical artery cases having some form of renal anomaly. 2
Genetic Counseling Considerations
Genetic counseling (Option A) is NOT indicated for isolated single umbilical artery, as isolated single umbilical artery shows no increased risk of aneuploidy. 2, 3
When single umbilical artery occurs with other structural abnormalities, the frequency of associated aneuploidy ranges from 4% to 50%, but this scenario specifically states no congenital anomalies were found. 2
If aneuploidy screening (cfDNA or serum screen) was negative or not previously performed, no additional genetic testing is needed for isolated single umbilical artery. 4
Enhanced Antenatal Surveillance Protocol
The appropriate management includes routine antenatal care with the following modifications:
Third-trimester ultrasound examination to evaluate fetal growth is recommended, as neonates with isolated single umbilical artery have increased rates of growth restriction. 4, 1, 2, 5
Consider weekly antenatal fetal surveillance beginning at 36 weeks of gestation, due to increased risks of stillbirth (OR 4.80,95% CI 2.67-8.62), polyhydramnios, oligohydramnios, placental abruption, and cord prolapse. 1, 2
Placental abnormalities occur more frequently (OR 3.63,95% CI 3.01-4.39) in isolated single umbilical artery pregnancies. 5
Why Termination is NOT Indicated
Termination of pregnancy (Option D) is absolutely NOT indicated for isolated single umbilical artery without additional anomalies. 1, 3
Studies show that neonates with isolated single umbilical artery who had no additional congenital or cytogenetic abnormality were completely normal at birth and during the neonatal period. 6
Postnatal Planning
- The pediatric team should be notified of the prenatal findings at delivery, as postnatal examination of infants with prenatal diagnosis of isolated single umbilical artery revealed structural anomalies in up to 7% of fetuses that were not detected prenatally. 1