Which mechanism best explains why ACE inhibitors are contraindicated throughout pregnancy rather than merely avoided in the first trimester?

• A They cross the placenta and cause fetal cardiac conduction defects
• B They increase uteroplacental blood flow and precipitate abruption
• C They induce maternal hyperkalemia that crosses into fetal circulation
• D They impair fetal renal development and function, causing oligohydramnios and skull hypoplasia ✓

Explanation

The fetoplacental circulation depends on angiotensin II to maintain efferent arteriolar tone and renal perfusion during development. ACE inhibitors block this, producing fetal renal failure, oligohydramnios, calvarial hypoplasia, limb contractures, and pulmonary hypoplasia, a pattern seen with exposure in the second and third trimesters. They are therefore contraindicated in all trimesters. The other options describe mechanisms of other drugs or effects that do not occur.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.