Unexpected Fetal Supraventricular Tachycardia Temporally Associated With Maternal Antihistamine Use: A Case Report

Fetal supraventricular tachycardia (SVT) represents the most common cause of sustained fetal tachyarrhythmia and may result in significant hemodynamic compromise when persistent. Data regarding the cardiovascular effects of maternal antihistamine use during pregnancy remain limited. We report a near‐term fetus with sustained SVT temporally associated with maternal ingestion of cetirizine and an antihistamine–decongestant combination for the treatment of allergic rhinitis. Owing to the persistence of the tachyarrhythmia during hospitalization, transplacental antiarrhythmic therapy with flecainide was initiated. After 48 h of treatment, successful rhythm control was achieved. Concurrent use of cetirizine and an antihistamine decongestant in a single dose during pregnancy resulted in sustained SVT in the fetus, necessitating treatment. Therefore, the use of cetirizine in the third trimester and antihistamine decongestants throughout pregnancy requires further investigation.