Tocolytic magnesium sulfate toxicity and unexpected neonatal death

A 31-year-old primigravida with twins had spontaneous rupture of the membranes at 32 weeks' gestation. On admission, because of contractions, the mother was started on tocolytic magnesium sulfate (MgSO4) along with betamethasone and prophylactic antibiotics. About a day later, she was found to have magnesium toxicity. Her serum total magnesium level was 9.0 mg/dl. Tocolysis was immediately discontinued. At cesarean delivery the following day, twin A, a female, died at 30 minutes of age despite a vigorous resuscitation. Although the preceding fetal heart rate patterns had been reassuring and the umbilical blood gases were normal, quite unexpectedly, the Apgar scores were 1/1/0. An autopsy revealed no anatomic abnormalities. Twin B, a female who survived, was also intubated at delivery. During her stay in the Neonatal Intensive Care Unit, she was found to have modestly elevated levels of serum cardiotroponin T. In our opinion, it is probable that the death of twin A can be directly attributed to magnesium sulfate toxicity. Neonatologists who attend deliveries should be aware that unexpected death may occur in babies who were exposed to high doses of tocolytic MgSO4.