A 36-week pregnant woman lies flat on her back during an ultrasound examination and develops sudden pallor, dizziness, and hypotension. Rolling her onto her left side promptly relieves the symptoms. The immediate mechanism responsible for this episode is:
- A Compression of the abdominal aorta, increasing afterload on the left ventricle
- B Compression of the inferior vena cava by the gravid uterus, reducing venous return ✓
- C Vasovagal stimulation from pressure on the pelvic splanchnic nerves
- D Acute reduction in uteroplacental blood flow causing reflex bradycardia
Correct answer: B. Compression of the inferior vena cava by the gravid uterus, reducing venous return
Explanation
In the supine position the term gravid uterus compresses the inferior vena cava against the vertebral column, sharply reducing venous return and hence cardiac output, producing the supine hypotension syndrome. Left lateral tilt displaces the uterus off the cava and restores preload. Aortic compression alone raises afterload rather than dropping pressure acutely, and vasovagal or placental-flow mechanisms do not explain the instant relief with repositioning.
Reference: Williams Obstetrics, 25th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.