Magnesium sulfate used in preterm labor has which of the following adverse effects?

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Magnesium sulfate acts as a calcium antagonist at the neuromuscular junction and as a CNS depressant. As serum levels rise, it blunts neuromuscular transmission and weakens respiratory muscles, leading to respiratory depression. This is the most important and potentially life-threatening adverse effect to monitor for when using magnesium sulfate to manage preterm labor. Clinically, watch for loss of deep tendon reflexes, drowsiness, shallow breathing, or decreased respiratory rate, and be prepared to stop the infusion and administer calcium gluconate if toxicity signs appear. Hyperglycemia, hyperkalemia, and hypothermia are not typical adverse effects of this medication in this context.