Magnesium sulfate‐induced blocked premature atrial contractions resulting in fetal bradyarrhythmia

Abstract

a b s t r a c tHere, we present a rare case of fetal bradyarrhythmia following magnesium sulfate therapy for preterm labor. After we switched treatment from ritodrine hydrochloride to magnesium sulfate at 25 weeks' gestation, the fetal heart rate dropped from 150 bpm to 80-100 bpm. Fetal echocardiography and magnetocardiography indicated bigeminy and trigeminy of blocked premature atrial contractions. It is well known that magnesium sulfate decreases the baseline and variability of fetal heart rate. Studies have reported a substantial decrease of 2-15 bpm in the baseline fetal heart rate, and magnesium has various effects on fetal heart rate patterns with a lower baseline fetal heart rate within the normal range of 110-160 bpm. This is the first report of magnesium sulfate-induced fetal bradyarrhythmia by prolongation of the refractory period of the atrioventricular node in the case of blocked premature atrial contractions. Clinicians should consider fetal bradyarrhythmia when the baseline fetal heart rate drops to o100 bpm after magnesium sulfate administration.