Rapid Normalization of Amniotic Fluid Index Following Discontinuation of Olmesartan: A Case Report

Background: Angiotensin II receptor blockers (ARBs) are commonly used for hypertension but are contraindicated in pregnancy due to risks of oligohydramnios, renal dysgenesis, and pulmonary hypoplasia from suppression of the fetal renin-angiotensin system. Olmesartan, a frequently prescribed ARB, has a longer receptor binding half-life and higher affinity than other ARBs, producing more potent and sustained antihypertensive effects. Emerging evidence suggests that stopping ARBs during pregnancy may allow recovery of amniotic fluid and renal function. Case: A 30-year-old primigravida with chronic hypertension presented at 24 weeks' gestation while taking olmesartan. Ultrasound revealed anhydramnios with a normal-appearing fetal genitourinary tract. Olmesartan was discontinued and replaced with labetalol. Within 2 weeks, the amniotic fluid index normalized, and subsequent ultrasounds showed sustained recovery. At 34 weeks, she delivered a viable male infant with reassuring renal function and only mild, improving calyceal dilation on postnatal ultrasound. Conclusion: This is, to our knowledge, the first reported case of reversible anhydramnios associated with first- and second-trimester olmesartan exposure. The favorable outcome highlights the potential for reversibility of ARB-related fetopathy with timely cessation. Clinicians should consider serial ultrasound monitoring before recommending termination, as early drug withdrawal may restore amniotic fluid and support normal neonatal outcomes.