## Correct Answer: B. 2 arteries, 1 vein The umbilical cord contains **two umbilical arteries and one umbilical vein**, a configuration that is constant and clinically important. The two arteries (right and left umbilical arteries) carry deoxygenated blood from the fetus to the placenta, while the single umbilical vein returns oxygenated blood from the placenta to the fetus. This asymmetry (2 arteries : 1 vein) is a fundamental embryological feature derived from the paired dorsal aortae and the vitelline venous system. The umbilical vein enters the fetus at the umbilicus and travels through the falciform ligament to the liver, where it connects to the ductus venosus, allowing blood to bypass hepatic circulation during fetal life. The two arteries branch from the internal iliac arteries (formerly hypogastric arteries) and are the only fetal arteries carrying deoxygenated blood. This 2:1 ratio is so consistent that finding a single umbilical artery (SUA) is considered an anatomical variant associated with increased risk of congenital anomalies and intrauterine growth restriction—a clinically significant finding in Indian obstetric practice during routine antenatal ultrasound screening. ## Why the other options are wrong **A. 1 artery, 1 vein** — This is wrong because it reverses the actual anatomy. The umbilical cord always contains two arteries, not one. A single umbilical artery is a pathological variant (not the normal state) associated with chromosomal abnormalities and IUGR. This option may trap students who confuse the fetal circulation pattern with the cord contents or who misremember the embryological origin of umbilical vessels. **C. 1 artery, 2 veins** — This is wrong because it inverts the normal ratio. There is only one umbilical vein in normal anatomy; the presence of two umbilical veins is extremely rare and anomalous. This option tests whether students have memorized the correct 2:1 arterial-to-venous ratio. The trap here is that students may think 'paired structures' apply equally to both arteries and veins, when in fact only the arteries are paired. **D. 2 arteries, 2 veins** — This is wrong because it incorrectly doubles the venous component. While the two arteries are correct, there is only one umbilical vein in normal fetal circulation. This option may trap students who assume symmetry in the umbilical cord or who confuse it with systemic circulation where arteries and veins are paired. The presence of two umbilical veins would be a rare congenital anomaly, not normal anatomy. ## High-Yield Facts - **Umbilical cord contents**: 2 arteries (deoxygenated blood to placenta) + 1 vein (oxygenated blood from placenta) = constant anatomical ratio - **Single umbilical artery (SUA)** is a variant found in ~0.5% of singleton pregnancies; associated with chromosomal abnormalities (trisomy 13, 18, 21) and IUGR—mandatory detailed fetal anomaly scan in Indian antenatal care - **Umbilical vein** enters fetus at umbilicus, travels in falciform ligament, connects to ductus venosus to bypass liver during fetal life - **Umbilical arteries** originate from internal iliac (hypogastric) arteries; are the only fetal arteries carrying deoxygenated blood—unique to fetal circulation - **Wharton's jelly** surrounds the three vessels in the umbilical cord, providing mechanical protection and preventing vessel compression during labor ## Mnemonics **2-1 Rule of Umbilical Cord** **2** Arteries (deoxygenated OUT to placenta) + **1** Vein (oxygenated IN from placenta). Remember: **A**rteries are **A**lways **2** (paired from aorta), **V**ein is **V**ery **1** (single return). **SUA = Suspect Anomalies** **S**ingle **U**mbilical **A**rtery = Screen for **S**tructural anomalies, **U**ndiagnosed **A**nomalies (trisomy 13/18/21), and **S**mall for **G**estational **A**ge (IUGR). Use in antenatal counseling. ## NBE Trap NBE may pair this with questions on single umbilical artery to test whether students confuse the normal anatomy (2 arteries) with the pathological variant (1 artery). Students who have only heard "SUA is important" may incorrectly select option A, thinking it is the normal state. ## Clinical Pearl In Indian antenatal ultrasound screening (routine at 18–22 weeks), identification of a single umbilical artery on color Doppler is a red flag requiring detailed fetal anatomy assessment and karyotyping counseling. The normal 2:1 ratio is so consistent that any deviation warrants investigation for chromosomal or structural anomalies. _Reference: Bailey & Love Ch. 73 (Obstetrics); Robbins Ch. 10 (Fetal Development)_
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