ACOG's Committee on Obstetric Practice and the Society for Maternal-Fetal Medicine continue to support the use of magnesium sulfate in obstetric care.

The U.S. Food and Drug Administration (FDA) has recently changed the classification of magnesium sulfate injection from Category A to Category D. However, this change was based on a small number of neonatal outcomes in cases in which the average duration of exposure was 9.6 weeks. ACOG's Committee on Obstetric Practice and the Society for Maternal-Fetal Medicine continue to support the use of magnesium sulfate in obstetric care for appropriate conditions and for appropriate, short term (usually less than 48 hours) durations of treatment.

http://www.fda.gov/Drugs/DrugSafety/ucm353333.htm 

American Congress of Obstetricians and Gynecologists
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