A 28-year-old primigravida at 20 weeks of gestation attends her routine antenatal clinic visit. During the anomaly scan, a single umbilical artery is noted incidentally. Which is the most common congenital anomaly associated with single umbilical artery?

Explanation

## Single Umbilical Artery (SUA) and Associated Anomalies ### Overview **Key Point:** Single umbilical artery occurs in 0.5–1% of singleton pregnancies and is associated with congenital anomalies in 20–40% of cases. ### Most Common Associated Anomalies | Anomaly | Frequency | Clinical Significance | |---------|-----------|----------------------| | **Renal agenesis / dysplasia** | 30–40% | Most common; bilateral agenesis incompatible with life | | Cardiac defects | 20–25% | VSD, ASD, TOF, PDA | | GI anomalies | 10–15% | Duodenal atresia, tracheo-esophageal fistula | | CNS anomalies | 5–10% | Anencephaly, spina bifida | | Limb anomalies | 5–10% | Polydactyly, syndactyly | ### Pathophysiology **High-Yield:** The umbilical artery develops from the paired dorsal aortae. Regression of one artery occurs early in embryogenesis (weeks 4–8), suggesting a developmental insult during this critical window. This timing correlates with organogenesis, explaining the high association with renal and cardiac anomalies. ### Clinical Pearl **Key Point:** Isolated SUA (without other anomalies on detailed ultrasound) carries a lower risk of adverse outcome (~10–15%), but detailed fetal anatomy survey and postnatal renal ultrasound are mandatory. ### Management Implications - Detailed fetal anatomy scan (cardiac, renal, GI, CNS) - Fetal echocardiography if cardiac anomaly suspected - Postnatal renal ultrasound within first week of life - Genetic counselling if multiple anomalies present **Mnemonic: SCAR** — Single umbilical artery → **C**ardiac, **A**nomalies, **R**enal (most common).