Increased pediatric mortality has been noted when used for pre-term labor. Additionally, neonatal fractures have been reported. Retrospective studies and case reports show fetal abnormalities such as hypocalcemia, skeletal demineralization, osteopenia, congenital rickets, and other skeletal abnormalities with continuous maternal administration for more than 5 to 7 days. Magnesium sulfate readily crosses the placenta and may produce hypotonia and hypotension fetal serum concentrations approximate those of the mother. There are no controlled data in human pregnancy. Avoid use in the 2 hours before delivery unless it is the only therapy available for eclamptic seizures. Inform women that efficacy and safety for preterm labor has not been established, and that use beyond 5 to 7 days can cause fetal abnormalities. Use for preterm labor should be by obstetrical personnel in a hospital with appropriate obstetrical care facilities. Continuous IV infusion, especially more than 24 hours before delivery, can result in magnesium toxicity, including neuromuscular or respiratory depression, in the newborn.
Intravenous use beyond 5 to 7 days can cause fetal abnormalities. Use is recommended only if clearly needed and the benefit outweighs the risk. Magnesium sulfate Pregnancy and Breastfeeding Warnings
