Chronic Hypertension in Pregnancy
A 36-year-old woman with chronic hypertension taking hydrochlorothiazide and losartan reports two months of amenorrhea. She feels well. Blood pressure is 132/84 mm Hg, urine dipstick shows no protein, and a urine pregnancy test is positive. Ultrasound confirms an 8-week intrauterine pregnancy. Which of the following is the most appropriate treatment adjustment?
- A.Continue the current regimen unchanged
- B.Stop all antihypertensive agents now
- C.Stop losartan and start enalapril
- D.Stop losartan and start methyldopaCorrect
Explanation
Angiotensin receptor blockers and angiotensin-converting enzyme inhibitors are contraindicated throughout pregnancy and must be stopped as soon as pregnancy is confirmed. Blockade of the fetal renin-angiotensin system impairs renal perfusion and urine production, producing oligohydramnios with pulmonary hypoplasia, limb contractures, calvarial hypoplasia, renal tubular dysgenesis and neonatal anuria; the risk is greatest in the second and third trimesters. Because both drug classes share the mechanism, switching from losartan to enalapril is no safer. The pregnancy-compatible agents are methyldopa, labetalol and nifedipine, and either methyldopa or labetalol is a standard first choice for chronic hypertension in pregnancy. Antihypertensive therapy should not simply be withdrawn, because uncontrolled chronic hypertension increases the risk of superimposed preeclampsia, placental abruption, fetal growth restriction and stroke. Thiazides are generally discontinued or avoided because of concerns about plasma volume contraction, although continuation of a pre-existing thiazide is not absolutely prohibited. Low-dose aspirin from 12 weeks is recommended for preeclampsia prophylaxis in women with chronic hypertension, and serial growth scans and blood pressure surveillance are needed. Atenolol is also avoided because of fetal growth restriction.
Why each option
- A.
- Continuing losartan exposes the fetus to oligohydramnios, renal failure, skull hypoplasia and death; it must be stopped immediately.
- B.
- Stopping all therapy risks uncontrolled hypertension with abruption, superimposed preeclampsia, growth restriction and maternal stroke.
- C.
- Enalapril is an ACE inhibitor and shares the same fetal renin-angiotensin toxicity as losartan, so it is not a safe substitute.
- D.
- Correct. Methyldopa is a well-established pregnancy-safe antihypertensive; labetalol or nifedipine are the accepted alternatives.
Reference: ACOG Practice Bulletin 203: Chronic Hypertension in Pregnancy, 2019
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