A pregnant woman at 32 weeks complains of positional dizziness and near-syncope when lying supine. Her blood pressure drops from 120/80 to 90/60 mmHg in the supine position. What is the underlying mechanism?

• A Compression of the aorta by the uterus reducing peripheral resistance
• B Progesterone-induced vasovagal reflex triggered by supine position
• C Diaphragmatic elevation reducing pulmonary venous return
• D Compression of the inferior vena cava by the gravid uterus reducing venous return and cardiac preload ✓

Explanation

Supine hypotensive syndrome of pregnancy occurs when the gravid uterus (particularly after 20 weeks) compresses the inferior vena cava against the lumbar vertebrae in the supine position, reducing venous return to the right heart and thereby decreasing cardiac output and blood pressure. Relief is immediate upon left lateral decubitus positioning. Clinically, pregnant women beyond 20 weeks should avoid the supine position for prolonged periods and should sleep in the left lateral position.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.