What is magnesium sulfate used for in obstetrics and what are its side effects?

Magnesium sulfate is used in obstetrics to prevent and treat seizures in preeclampsia and eclampsia, and as a tocolytic to delay preterm labor for up to 48 hours to allow administration of corticosteroids for fetal lung maturity. It works by decreasing neuromuscular excitability. Side effects include flushing, sweating, hypotension, decreased deep tendon reflexes, and respiratory depression. The therapeutic serum level is 4 to 7 milliequivalents per liter. Toxicity signs progress from loss of deep tendon reflexes to respiratory depression to cardiac arrest.