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, intention to breastfeed may be a more important determinant of breastfeeding initiation.[1] Postpartum use of intravenous magnesium sulfate for longer than 6 hours appears to delay the onset of lactation.[2,3] One group of experts recommends reserving postpartum magnesium sulfate prophylaxis for those women with persistent neurologic symptoms within 7 days of birth.[4]