The antihypertensive mechanism that makes labetalol preferred over pure beta-blockers in severe hypertension in pregnancy is best explained by:
- A Predominant beta-1 selective blockade reducing cardiac output without peripheral vasoconstriction
- B Direct smooth muscle relaxation via calcium channel antagonism in uteroplacental vessels
- C Combined alpha-1 and non-selective beta blockade producing vasodilation while reducing heart rate ✓
- D Central alpha-2 agonism reducing sympathetic outflow without affecting uterine blood flow
Correct answer: C. Combined alpha-1 and non-selective beta blockade producing vasodilation while reducing heart rate
Explanation
Labetalol is a combined alpha-1 (peripheral vasodilation) and non-selective beta-blocker (reduces HR and CO). This dual action lowers BP effectively without the pure reflex tachycardia of vasodilators or the decreased placental flow of pure beta-blockers. Pure beta-blockers reduce CO and can decrease uteroplacental perfusion. Methyldopa acts via central alpha-2 agonism. Nifedipine acts via calcium channel antagonism.
Reference: Williams Obstetrics, 26th ed.
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Written and medically reviewed by the StethoPrep medical team.