## **Core Concept**
The presence of a single umbilical artery (SUA) is a relatively common congenital anomaly that can be associated with various fetal malformations. Typically, the umbilical cord contains two arteries and one vein. The umbilical arteries are responsible for carrying deoxygenated blood from the fetus to the placenta, while the umbilical vein carries oxygenated blood from the placenta to the fetus. The absence or abnormal development of one umbilical artery can lead to an increased risk of certain congenital anomalies.

## **Why the Correct Answer is Right**
The correct answer, **C. Urinary tract**, is associated with SUA because the development of the umbilical arteries and the urinary system are closely related embryologically. The umbilical arteries arise from the anterior divisions of the internal iliac arteries, which also give rise to the superior vesical arteries that supply the bladder. Anomalies in the development of one umbilical artery have been linked to an increased risk of renal and urinary tract malformations, such as renal agenesis, ectopic kidney, and ureteral abnormalities.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While cardiac malformations can occur alongside SUA, they are not the most commonly associated anomalies. Cardiac issues can arise due to various factors and are a broad category of congenital anomalies.
- **Option B:** Gastrointestinal malformations can also occur with SUA but are less commonly associated compared to urinary tract anomalies.
- **Option D:** Skeletal malformations, though possible, are not the most frequently linked anomalies with SUA.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that the presence of a single umbilical artery is considered a marker for potential fetal anomalies, particularly of the **urinary tract**. When SUA is detected, detailed fetal ultrasound evaluation, including assessment of the kidneys and urinary tract, is recommended to identify any associated anomalies.

## **Correct Answer:** C. Urinary tract.