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Aortocaval compression in pregnancy — FRCA Primary MCQ

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HardPhysiologyAortocaval compression in pregnancyFRCA Primary

A 27-year-old woman at term lies supine for spinal anaesthesia and becomes pale with blood pressure 78/40 mmHg. Left uterine displacement improves the pressure. What is the most likely mechanism?

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Correct answer: E — Reduced systemic vascular resistance from progesterone

The gravid uterus can compress the inferior vena cava in the supine position, reducing venous return and cardiac output; left uterine displacement relieves this. Progesterone-mediated vasodilatation contributes to pregnancy physiology but does not explain the positional response. Aortic compression may also occur, but the immediate hypotension improved by tilt is classically from reduced venous return. The pearl is that neuraxial sympathectomy magnifies this effect.

Reference: RCoA Primary FRCA Syllabus 2026; Ganong's Review of Medical Physiology; West's Respiratory Physiology