Magnesium Sulfate and Premature Labor

Pregnant Hospital Patient with IV
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Magnesium sulfate, or mag for short, has been used in pregnancy for over 60 years. Mag was originally used solely to prevent seizures due to worsening preeclampsia, and it is still used for that reason. In modern days, magnesium sulfate is also used to slow or stop preterm labor, and to prevent injuries to the baby's brain.

Although mag infusions can have a lot of benefits for moms and babies, they aren't fun. Moms often complain about mag's side effects and don't like that it has to be given through an IV, in the hospital. Let's look more at the benefits and side effects of this very common drug in labor and delivery.

Uses of Magnesium Sulfate in Pregnant Women

Magnesium sulfate is commonly used on obstetrical floors, and for good reason. It's a well-studied drug, so doctors know very well how it affects moms and babies. It's also a useful medication, and can be used for these three main reasons:

  • Allow time to give steroids: Magnesium sulfate is a tocolytic that has been used to slow or stop premature labor. Research shows that mag, like other tocolytics, doesn't work very well to actually prevent preterm birth, but it may help stall labor for a short time. Doctors may treat preterm labor with 48 hours of mag, hoping to buy enough time to complete a course of steroids to help the baby's lungs develop.
  • Prevent seizures from eclampsia: Preeclampsia is a common complication of pregnancy that causes high blood pressure and protein in the urine. If not treated, preeclampsia can develop into eclampsia, a seizure disorder. The only cure for preeclampsia and eclampsia is delivery of the baby, but magnesium sulfate can help prevent seizures in women with severe preeclampsia.
  • Protect the preterm baby's brain: Premature babies, especially those who are born before about 32 weeks gestation, have immature brains at birth. As they grow, they are at risk for cerebral palsy, a disorder that affects movement and intelligence. Short-term (24 hours or less) infusions of magnesium sulfate have been shown to help protect the baby's brain by reducing the incidence of cerebral palsy.

    Side Effects 

    Although magnesium sulfate infusions lasting a week or less are considered safe for mom and for baby, they aren't always fun. Mag has a number of side effects that aren't dangerous but can be very uncomfortable.

    In moms, side effects of magnesium sulfate can include:

    • Flushing or hot flashes
    • Feeling tired and lethargic
    • Nausea and vomiting
    • Dizziness
    • Blurred vision
    • Muscle weakness

    In rare cases, respiratory depression can occur. This can be reversed with a calcium infusion and is more common in women with kidney problems.

    Magnesium sulfate does cross to the baby, and babies may be born with side effects from mag. Low Apgar scores and poor muscle tone at birth are the most common side effects of mag in babies. These side effects are usually gone in a day or so and don't cause long-term problems. Pregnant women shouldn't receive mag for longer than 5 to 7 days, as long-term mag therapy can cause low calcium in the baby's bones.

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    Article Sources
    • American College of Obstetricians and Gynecologists. "Magnesium Sulfate Use in Obstetrics." Sept. 2013.
    • Merrill, L., "Magnesium Sulfate During Anticipated Preterm Birth for Infant Neuroprotection." Feb-Mar 2013. Nursing for Women's Health. 17;42-51.
    • Riaz, M., Porat, R., Brodsky, NL, Hurt, H. "The Effects of Maternal Magnesium Sulfate Treatment on Newborns: A Prospective Controlled Study." Nov-Dec 1998. Journals in Perinatology 18(6 Pt 1):449-54.
    • Smith, J., Lowe, R., Fullerton, J., Currie, S., Harris, L., and Felker-Kantor, E. "An Integrative Review of the Side Effects Related to the use of Magnesium Sulfate for Pre-eclampsia and Eclampsia Management." Feb. 2013. BMC Pregnancy Childbirth 13:34.
    • US Food and Drug Administration. "Magnesium Sulfate: Drug Safety Communication - Recommendation Against Prolonged Use in Pre-term Labor" May 30, 2013.