Short-term Magnesium Sulfate Use Appropriate, ACOG, SMFM Say

Laurie Barclay, MD

December 29, 2015

Short-term (usually less than 48 hours) use of magnesium sulfate in obstetric care is appropriate for certain conditions and durations of treatment, according to a committee opinion from the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine. The new recommendations, which update the previous opinion from September 2013, are published in the January issue of Obstetrics and Gynecology.

Appropriate indications for magnesium sulfate use in obstetric care are:

  • the prevention and treatment of seizures in women with preeclampsia or eclampsia,

  • fetal neuroprotection before anticipated early preterm (less than 32 weeks of gestation) delivery, and

  • short-term prolongation of pregnancy (up to 48 hours) to allow antenatal corticosteroid administration to pregnant women at risk for preterm delivery within 7 days.

"The American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine have long supported the short-term use of magnesium sulfate in obstetric care for appropriate conditions and for appropriate durations of treatment," according to the opinion. "The U.S. Food and Drug Administration (FDA) advises against use of magnesium sulfate injection for more than 5–7 days to stop preterm labor in pregnant women. Based on this, the drug classification was changed from Category A to Category D, and the labeling was changed to include this new warning information."

However, the groups note that the FDA's concerns were based on reports of fetal and neonatal bone demineralization and fractures associated with long-term in utero exposure to magnesium sulfate (average duration, 9.6 weeks; total maternal dose, 3700 g, both of which greatly exceed those currently recommended for obstetric use).

The groups recommend that practitioners not stop using magnesium sulfate for the indications presented earlier, based on the FDA reclassification, because prolonged use of magnesium sulfate is never indicated in any of these conditions. The FDA's change in the pregnancy classification of magnesium sulfate therefore addresses an unindicated and nonstandard use.

"Magnesium sulfate has been used in obstetrics for decades, and thousands of women have been enrolled in clinical trials that studied the efficacy of prenatal magnesium sulfate for a variety of conditions," according to the opinion. "Concerns about fetal and neonatal bone demineralization and fracture have not been raised from these studies, including recent trials of magnesium for neuroprotection."

The authors have disclosed no relevant financial relationships.

Obstet Gynecol. 2016;127:195. Abstract

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