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 medication.

Magnesium sulfate is sometimes used as a tocolytic medication 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 medication 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

---

Some hospitals use magnesium sulfate for preterm labor.² 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 , and the mother's amniotic sac has not broken.
• The mother is healthy.
• The fetus is alive and not in distress.
• Another tocolytic medication has not slowed uterine contractions.
• The mother is at risk of suffering serious side effects of beta-sympathetic medications (ritodrine and terbutaline) due to conditions such as diabetes, heart disease, or lung disease.
• Treatment with other tocolytic medications has been stopped because of side effects.

How Well It Works

---

Studies have shown that magnesium sulfate is unlikely to stop preterm labor.³ It may also cause complications for mother and baby.¹

Side Effects

---

Side effects are common with magnesium sulfate and can affect both the mother and fetus. Side effects are closely monitored and can include:

• Muscle weakness.
• Lack of energy and drowsiness.
• Decreased effort in breathing (respiratory depression).
• Low blood pressure and fast pulse.

These side effects can decrease over the duration of treatment and go away when the medication is stopped.

One study suggests that magnesium sulfate may cause greater risks to the fetus than other medicines used to stop preterm labor.⁴

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

What To Think About

---

Magnesium sulfate affects both a mother and her fetus. This medication:

• May reduce risks of cerebral palsy in the premature newborn if preterm labor progresses on to preterm delivery during treatment.⁵ Further research is necessary to confirm this.
• Affects a mother's central nervous system. Part of normal care when intravenous magnesium sulfate is given includes checking the mother's reflexes, usually every 2 to 4 hours, while she is on this medication.
• Affects the fetus's central nervous system. If a mother is given large doses of magnesium sulfate, the newborn may have trouble breathing immediately after birth. However, this problem is easily treated with medication. Some studies show that magnesium sulfate may increase the risk of death for the baby.¹
• Can lower a mother's blood pressure and increase her heart rate. Her blood pressure and pulse are checked frequently for the first few hours of treatment.
• Leaves the mother's body through her urine. The amount of urine she produces is closely monitored to ensure that the medication does not build up in her bloodstream.

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. Cunningham FG, et al. (2005). Preterm birth. In Williams Obstetrics, 22nd ed., pp. 855–880. New York: McGraw-Hill.

3. Haas DM (2005). Preterm birth, search date June 2005. Online version of Clinical Evidence (14): 1–20.

4. Crowther CA, et al. (2006). Magnesium sulphate for preventing preterm birth in threatened preterm labour. Cochrane Database of Systematic Reviews (1). Oxford: Update Software.

5. Crowther CA, et al. (2003). Effect of magnesium sulfate given for neuroprotection before preterm birth: A randomized controlled trial. JAMA, 290(20): 2669–2676.

Credits

---

Author	Kathe Gallagher, MSW
Editor	Kathleen M. Ariss, MS
Associate Editor	Pat Truman, MATC
Primary Medical Reviewer	Joy Melnikow, MD, MPH - Family Medicine
Primary Medical Reviewer	Kathleen Romito, MD - Family Medicine
Specialist Medical Reviewer	William Gilbert, MD - Perinatology
Last Updated	January 19, 2007