What to do if a pregnant woman at 18 weeks gestation is found to have a single umbilical artery (SUA) with no congenital anomalies during a routine anomaly scan?

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Management of Isolated Single Umbilical Artery at 18 Weeks

For a pregnant woman at 18 weeks with an isolated single umbilical artery (SUA) and no congenital anomalies, the correct answer is C - Routine ANC with enhanced surveillance, specifically including a comprehensive cardiac anatomy assessment now, third-trimester growth ultrasound, and consideration of weekly antenatal surveillance beginning at 36 weeks. 1

Initial Assessment and Cardiac Evaluation

A comprehensive assessment of cardiac anatomy (CPT code 76811 ultrasound) should be performed immediately, as cardiovascular and renal systems are the most commonly affected when SUA occurs with structural abnormalities. 1 However, if the required cardiac views are adequately visualized and normal during this detailed anatomic survey, fetal echocardiography is not routinely warranted. 1 This is a critical distinction—you need a thorough cardiac assessment, but not necessarily a formal fetal echo if the anatomy scan cardiac views are complete and normal.

Why Not Genetic Counseling or Aneuploidy Testing?

For fetuses with isolated SUA, no additional evaluation for aneuploidy is recommended, regardless of whether previous aneuploidy screening results were low risk or screening was declined. 1 This is because isolated SUA (without other structural or chromosomal abnormalities) carries no increased risk of aneuploidy. 1

The evidence is clear on this point:

  • When SUA occurs with one or multiple structural abnormalities, aneuploidy risk ranges from 4% to 50% 1
  • However, for isolated SUA with no other abnormalities, there is no increased aneuploidy risk 1

Therefore, genetic counseling (Option A) is not indicated unless other anomalies are subsequently discovered.

Why Not Routine Echocardiography?

While cardiovascular anomalies are among the most common structural defects associated with SUA 1, fetal echocardiography is not routinely warranted if the required cardiac views are adequately visualized and normal on the comprehensive anatomic ultrasound. 1 This means Option B (ECHO) is not automatically required—only if the standard cardiac assessment is inadequate or abnormal.

Why Termination is Not Indicated

Termination of pregnancy (Option D) is absolutely not indicated for isolated SUA. The condition itself, when truly isolated, does not represent a lethal or severely debilitating fetal condition. While isolated SUA does carry some increased risks (discussed below), these are manageable with appropriate surveillance and do not justify pregnancy termination.

Enhanced Surveillance Protocol

The key to managing isolated SUA is enhanced monitoring due to conflicting evidence about pregnancy complications:

Third-Trimester Growth Assessment

A third-trimester ultrasound examination to evaluate growth is recommended. 1 This is critical because:

  • Studies show conflicting evidence regarding fetal growth restriction (FGR) risk 1
  • Some studies demonstrate increased risk of FGR, while others show no increased incidence 1
  • Research indicates 50% of fetuses with isolated SUA may demonstrate growth restriction 2
  • Birth weight <10th percentile occurs more frequently (OR 2.1; 95% CI 1.44-2.93) 3

Antenatal Surveillance

Consider weekly antenatal fetal surveillance beginning at 36 0/7 weeks of gestation for fetuses with isolated SUA. 1 This recommendation is based on:

  • A case-control study showing SUA associated with increased odds of stillbirth (OR 4.80; 95% CI 2.67-8.62) 1
  • Increased risks of polyhydramnios, oligohydramnios, placental abruption, cord prolapse, and perinatal mortality 1
  • Increased rates of prematurity and adverse neonatal outcomes 4

Additional Pregnancy Risks to Monitor

Beyond growth restriction and stillbirth, isolated SUA is associated with:

  • Polyhydramnios (OR 3.32; 95% CI 1.22-9.04) 3
  • Preterm delivery <34 weeks (OR 4.662; 95% CI 2.346-9.195) 3
  • Cesarean delivery for fetal distress (OR 2.72; 95% CI 1.53-4.81) 3
  • Placental abnormalities (OR 3.25; 95% CI 2.14-4.93) 3, 4
  • NICU admission (OR 2.71; 95% CI 1.87-3.91) 3

Postnatal Considerations

At the time of delivery, the pediatric provider should be notified of the prenatal findings. 1 This is important because postnatal examination of infants with prenatal diagnosis of isolated SUA revealed structural anomalies in up to 7% of fetuses in one study. 1 Additionally, neonatal anomalies were present in 2.6% of fetuses with isolated SUA. 3

Common Pitfalls to Avoid

  • Do not order routine fetal echocardiography if the comprehensive cardiac assessment on the anatomy scan is adequate and normal 1
  • Do not pursue genetic testing or amniocentesis for isolated SUA without other concerning findings 1
  • Do not provide false reassurance—while isolated SUA has better outcomes than non-isolated SUA, it still requires enhanced surveillance due to increased stillbirth risk 1
  • Do not miss the third-trimester growth scan—this is essential for detecting FGR, which occurs in a significant proportion of cases 1

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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