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Magnesium Sulfate for Preterm Labor

Examples

Generic Name
magnesium sulfate

Magnesium sulfate is most commonly used for the treatment of preeclampsia during pregnancy. Use of magnesium for the treatment of preterm labor or preeclampsia is an unlabeled use of the medicine.

Magnesium sulfate is sometimes used as a tocolytic medicine to slow uterine contractions during preterm labor. But studies show it does not stop preterm labor and it may cause complications for both mother and baby.1

Magnesium sulfate is usually given through a vein (intravenously) until contractions have slowed and the mother's cervix has stopped thinning (effacing) or opening (dilating).

How It Works

This medicine is thought to affect the action of calcium in the body, and calcium must be present for the muscles of the uterus to contract.

Why It Is Used

Magnesium sulfate may be used to stop preterm labor when:

  • Labor needs to be delayed for 24 to 48 hours to:
    • Let corticosteroids given to the mother help fetal lungs mature.
    • Provide time to move a mother to a hospital that offers neonatal intensive care, if her local hospital does not.
  • Regular contractions of the uterus have thinned (effaced) the cervix and opened (dilated) it less than 4 cm, and the mother's amniotic sac has not broken.
  • The mother is healthy.
  • The fetus is alive and not in distress.
  • Another tocolytic medicine has not slowed uterine contractions.
  • Treatment with other tocolytic medicines has been stopped because of side effects.

If preterm labor is likely to lead to preterm delivery, magnesium sulfate may be used to reduce the risk of cerebral palsy in the premature newborn.2More research is needed to find out how well this works.3

How Well It Works

Studies have shown that magnesium sulfate is unlikely to stop preterm labor.4 It may also cause complications for mother and baby.1

Side Effects

Common side effects of this medicine include:

  • Muscle weakness and lack of energy.
  • Blurry vision.
  • Slurred speech.
  • Headache.
  • Nausea and vomiting.
  • Flushing.
  • Stuffy nose.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

In rare cases, symptoms of magnesium toxicity (nausea, muscle weakness, loss of reflexes) occur during magnesium sulfate treatment. The medicine calcium gluconate is given to treat the problem.

Magnesium sulfate:

  • Affects the central nervous system (brain and spinal cord) of the mother. Part of normal care when intravenous magnesium sulfate is given includes checking the mother's reflexes. If too much magnesium sulfate is given, the mother's reflexes will be slowed. Reflexes are usually checked about every 2 to 4 hours while the mother is on this medicine.
  • Affects the fetus's central nervous system. If this medicine has been given to the mother in large doses and the baby is born before the drug has had time to clear the mother's body, the baby may have temporary problems with breathing right after birth. These problems are quickly reversed with medicine.
  • Leaves the mother's body in her urine. The amount of urine she produces is closely monitored to ensure that this medicine does not build up in her bloodstream.

Mothers on magnesium sulfate are closely monitored. Blood pressure and pulse are checked about every 30 minutes for at least the first few hours of treatment.

Complete the new medication information form (PDF)(What is a PDF document?) to help you understand this medication.

References

Citations

  1. Grimes DA, Nanda K (2006). Magnesium sulfate tocolysis: Time to quit. Obstetrics and Gynecology, 108(4): 986–989.
  2. Rouse DJ, et al. (2008). A randomized, controlled trial of magnesium sulfate for the prevention of cerebral palsy. New England Journal of Medicine, 359(9): 895–905.
  3. American College of Obstetricians and Gynecologists (2010). Magnesium sulfate before anticipated preterm birth for neuroprotection. ACOG Committee Opinion No. 455. Obstetrics and Gynecology, 115(3): 669–671.
  4. Haas DM (2010). Preterm birth, search date June 2009. Online version of BMJ Clinical Evidence: http://www.clinicalevidence.com.

Credits

By Healthwise Staff
Primary Medical Reviewer Sarah Marshall, MD - Family Medicine
Specialist Medical Reviewer William Gilbert, MD - Maternal and Fetal Medicine
Last Revised January 10, 2011

Last Revised: January 10, 2011

Author: Healthwise Staff

Medical Review: Sarah Marshall, MD - Family Medicine & William Gilbert, MD - Maternal and Fetal Medicine

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