Magnesium Sulfate During Pregnancy: Uses and Side Effects

What does the evidence say about magnesium sulfate during pregnancy?

1. Magnesium sulfate is an approved medication for seizure risk-reduction guidance in preeclampsia and eclampsia, not a general-purpose prenatal magnesium product. 1
2. A systematic review of randomized trials found antenatal magnesium sulfate was associated with lower cerebral palsy risk among children born after imminent preterm delivery. 2
3. A broad review found no clear difference in perinatal death in randomized comparisons of antenatal magnesium sulfate with placebo or no magnesium sulfate. 3
4. A meta-analysis of ten trials did not find more eclamptic seizures with postpartum magnesium sulfate courses of 12 hours or less than with 24 hours. The data were underpowered for firm conclusions, so the result does not establish that shorter courses are equivalent for every patient. 4
5. Flushing and warmth are common with standard magnesium sulfate administration; excessive levels can affect reflexes, breathing, blood pressure, and heart conduction, which is why clinical monitoring matters. 1

Is magnesium sulfate safe in each trimester?

• First trimester. Magnesium sulfate is not a routine first-trimester supplement. If it is considered in early pregnancy, the reason and route should be reviewed by the prescribing team.
• Second trimester. In the second trimester, magnesium sulfate may be used in hospital for a pregnancy complication or when an early birth is anticipated. The indication determines the monitoring plan.
• Third trimester. In the third trimester, magnesium sulfate is commonly discussed with severe preeclampsia, eclampsia, or imminent very preterm birth. Hospital staff monitor reflexes, breathing, urine output, and clinical response.