Single Umbilical Artery: Associated Findings
When a single umbilical artery (two-vessel cord) is identified at delivery, it is most strongly associated with major fetal malformations, particularly cardiovascular and renal anomalies, though the 80% figure cited in option D is incorrect—the actual rate is much lower.
Key Associations with Single Umbilical Artery
Structural Malformations
The most significant associations are with major congenital anomalies, not an 80% rate as suggested in the question options. The evidence shows:
- Cardiovascular anomalies are strongly associated with SUA, with odds ratios ranging from 5.9 to 20.3 for various cardiac defects 1, 2, 3
- Renal anomalies show a 3-fold increased risk (adjusted OR 3.0,95% CI 1.9-4.9), with approximately 16% of isolated SUA cases having some form of renal anomaly, though about half are minor or self-limiting 2, 4
- Gastrointestinal atresias demonstrate particularly strong associations, with ORs of 25.8 for esophageal atresia and 20.3 for anorectal atresia 3
Chromosomal Abnormalities
When SUA occurs with other structural abnormalities, the frequency of associated aneuploidy ranges from 4% to 50% 1. However:
- Isolated SUA (without other anomalies) shows no increased risk of aneuploidy 1
- Trisomy 18 and 13 show equally strong associations (OR 14.4 and 13.6, respectively) when SUA is present with other findings 3
- Trisomy 21 risk is doubled (OR 2.1) 3
Perinatal Morbidity and Mortality
Contrary to option C suggesting "low fetal mortality," SUA is actually associated with significantly increased mortality risk:
- 5-fold increased risk of adverse perinatal outcome (OR 5.06,95% CI 4.26-6.02) 5
- Nearly 5-fold increased risk of stillbirth (OR 4.80,95% CI 2.67-8.62) 1
- 5.6-fold increased risk of perinatal and intrauterine death (OR 5.62,95% CI 4.69-6.73) 5
- 73% increased risk of preterm birth 5
- 2-fold increased risk of intrauterine growth restriction (adjusted OR 2.1,95% CI 1.6-2.7), even after excluding fetuses with known anomalies 2
Risk Factors
The following maternal factors increase the odds of SUA 3:
- High parity (≥4 pregnancies)
- Maternal smoking
- Pregestational diabetes mellitus
- Epilepsy
- Chronic hypertension
- Previous cesarean delivery
- Conception via assisted reproductive technology
Clinical Context: Answering the Multiple Choice Question
Option B (Maternal diabetes) is the correct answer among the choices provided, as pregestational diabetes is a documented risk factor for SUA 3.
However, it's critical to understand that:
- Option D is misleading: While major fetal malformations ARE associated with SUA, the 80% figure is grossly inflated. In live-born infants, the mean incidence of congenital malformation with SUA is approximately 27% 4, and in isolated SUA cases, postnatal examination reveals structural anomalies in only up to 7% 1
- Option C is incorrect: SUA is associated with HIGH, not low, fetal mortality 1, 5
- Option A (race): No specific racial predisposition is documented in the high-quality guidelines reviewed
Clinical Management Implications
When SUA is identified, the following approach is warranted:
- Comprehensive anatomic survey with particular attention to cardiovascular and renal systems 1, 6, 7
- Third-trimester ultrasound to evaluate fetal growth 1, 6, 7
- Weekly antenatal surveillance beginning at 36 weeks gestation for isolated SUA 1, 6, 7
- Notification of pediatric providers at delivery, as up to 7% may have structural anomalies not detected prenatally 1, 6, 7