Is Magnesium Sulfate safe while breastfeeding?

Summary of use during breastfeeding

Intravenous magnesium increases milk magnesium concentrations only slightly and oral absorption of magnesium by the infant is poor, so maternal magnesium therapy is not expected to affect the breastfed infant's serum magnesium. Although intravenous magnesium sulfate given prior to delivery might affect the infant's ability to breastfeed, postpartum use of intravenous magnesium sulfate for 24 hours appears to delay the onset of lactation compared to shorter durations of 6 to 12 hours.[1,2] Intention to breastfeed may be an important determinant of breastfeeding initiation.[3] One group of experts recommends reserving postpartum magnesium sulfate prophylaxis for those women with persistent neurologic symptoms within 7 days of birth.[4]

Effects on the breastfed infant

Relevant published information was not found as of the revision date.

Effects on milk supply

One mother who received intravenous magnesium sulfate for 3 days for pregnancy-induced hypertension had lactogenesis II delayed until day 10 postpartum. No other specific cause was found for the delay, although a complete work-up was not done.[6] A subsequent controlled clinical trial found no evidence of delayed lactation in mothers who received intravenous magnesium sulfate therapy.[7] Another study found that among women with severe pre-eclampsia who received intravenous magnesium sulfate for up to one day postpartum and who intended to breastfeed, 85% of infants receiving routine well-baby care and 69% of those admitted to the NICU, breastfeeding was successfully initiated.[3]

A study randomized women with preeclampsia to receive intravenous magnesium sulfate for either 6 or 24 hours postpartum. There was no difference in the rate of eclampsia between the two groups. However, those who received the infusion for 24 hours had a delayed onset of lactation, 36.5 hours compared with 25.7 hours in the 6-hour group.[8]

A prospective, multicenter, randomized, controlled trial in 9 Latin American maternity hospitals compared patients with severe pre-eclampsia who had received at least 8 grams of magnesium sulfate prior to placebo. Patients were randomized to continue magnesium sulfate for 24 hours postpartum (n = 555) or stopping the infusion (n = 558). The time to lactation was significantly delayed in those who received magnesium sulfate postpartum (24.1 vs. 17.1 hours).[9]

A study randomized pregnant women with moderate to severe pre-eclampsia to receive magnesium sulfate intravenously infused at the same dose (not specified) for 8 or 24 hours. In patients who received the 8-hour infusion, the mean time to initiate breastfeeding was 14.6 hours compared to 24.3 hours in the patients who received the 24-hour infusion, which was a statistically significant difference.[10]

A retrospective chart review of mothers who delivered at the University of Chicago found that intravenous magnesium sulfate during delivery was associated with over 60% reduced odds of breastfeeding initiation compared to mothers who received no magnesium.[11]

Levels in milk

Maternal Levels. Ten women with pre-eclampsia were given 4 grams of magnesium sulfate intravenously followed by 1 gram per hour until 24 hours after delivery. While the average serum magnesium was 35.5 mg/L in treated women compared to 18.2 mg/L in 5 untreated controls, colostrum magnesium levels at the time of discontinuation of the infusion was 64 mg/L in treated women and 48 mg/L in the controls. By 48 hours after discontinuation, colostrum magnesium levels were only slightly above control values and by 72 hours they were virtually identical to controls.[5]

Infant Levels. Relevant published information was not found as of the revision date.

Alternatives LactMed lists

• Magnesium Hydroxide
• Psyllium
• Sodium Picosulfate
• Sodium Phosphate