Magnesium sulfate Pregnancy and Breastfeeding Warnings

Brand names: Epsom Salt, Sulfamag

Medically reviewed by Drugs.com. Last updated on Mar 17, 2025.

Magnesium sulfate Pregnancy Warnings

Use is recommended only if clearly needed and the benefit outweighs the risk.

AU TGA pregnancy category: D
US FDA pregnancy category: Not assigned

Risk summary: Prolonged administration of this drug (beyond 5 to 7 days) during pregnancy can cause fetal abnormalities. Retrospective studies and case reports have shown that extended maternal exposure can lead to fetal hypocalcemia, skeletal demineralization, osteopenia, congenital rickets, and other skeletal abnormalities.

Comments:
-Continuous IV infusion, especially more than 24 hours before delivery, can result in magnesium toxicity, including neuromuscular or respiratory depression, in the newborn.
-Use for preterm labor should be by obstetrical personnel in a hospital with appropriate obstetrical care facilities.
-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.
-Avoid use in the 2 hours before delivery unless it is the only therapy available for eclamptic seizures.
-Monitor fetal heart rate.

Animal studies have not been reported. There are no controlled data in human pregnancy.

Magnesium sulfate readily crosses the placenta and may produce hypotonia and hypotension; fetal serum concentrations approximate those of the mother. Additionally, neonatal fractures have been reported. Increased pediatric mortality has been noted when used for pre-term labor. If administered in the 2 hours preceding delivery, the neonate may have signs of hypermagnesemia, including respiratory and neuromuscular depression.

AU TGA pregnancy category D: Drugs which have caused, are suspected to have caused or may be expected to cause, an increased incidence of human fetal malformations or irreversible damage. These drugs may also have adverse pharmacological effects. Accompanying texts should be consulted for further details.

US FDA pregnancy category Not Assigned: The US FDA has amended the pregnancy labeling rule for prescription drug products to require labeling that includes a summary of risk, a discussion of the data supporting that summary, and relevant information to help health care providers make prescribing decisions and counsel women about the use of drugs during pregnancy. Pregnancy categories A, B, C, D, and X are being phased out.

See references

Magnesium sulfate Breastfeeding Warnings

Safety has not been established; use only if clearly needed.

Excreted into human milk: Yes

Comments:
-The concentration of magnesium in breast milk is approximately twice that of maternal serum concentrations.
-50 to 90% of magnesium in breast milk is absorbed.
-Magnesium is cleared from breast milk within 24 hours of cessation of intravenous magnesium

See references

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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