Letters to the Editor

Magnesium Sulfate in Women with Threatened Preterm Birth

Am Fam Physician. 2010 Dec 1;82(11):1310-1312.

Original Article: Preterm Labor

Issue Date: February 15, 2010

Available at: http://www.aafp.org/afp/2010/0215/p477.html

to the editor: I appreciated Dr. Sayres' thoughtful review on preterm labor. However, the role of magnesium sulfate in the management of preterm labor deserves further comment. As Dr. Sayres noted, a 2002 Cochrane systematic review concluded that magnesium sulfate is ineffective in tocolysis1; it is therefore no longer recommended for routine use as a tocolytic.2 In contrast, physicians should consider antenatal use of magnesium sulfate in women with threatened preterm birth to reduce the infant's risk of cerebral palsy.

Cerebral palsy disproportionately affects preterm infants, with an incidence of 4 to 8 percent among infants with a very low birth weight.3 Researchers have postulated that magnesium sulfate might protect the infant brain from cerebral palsy by assisting in glutamate homeostasis; by causing vasodilation, which leads to increased cerebral blood flow; or by reducing free radicals.3 At least five prospective, randomized controlled trials have examined the use of magnesium sulfate specifically for the prevention of cerebral palsy in preterm infants.4 A recent Cochrane systematic review (n = 6,145 infants) found that infants exposed to antenatal magnesium sulfate had a significantly lower risk of cerebral palsy (relative risk = 0.68; 95% confidence interval, 0.54 to 0.87).4 No statistically significant effect on infant mortality was detected (relative risk = 1.04; 95% confidence interval, 0.92 to 1.17), nor were there any significant effects on major maternal complications.

Based on these findings, some tertiary care centers have instituted protocols for neuroprophylaxis in women with threatened preterm delivery at 32 weeks' gestation or less. One protocol involves a 6-g loading dose over 20 to 30 minutes, followed by an infusion of 2 g per hour for up to 12 hours, at which point the risk of imminent delivery is reassessed and the infusion discontinued, if indicated.5

Further study may reveal the optimal dosage of magnesium sulfate and its specific risks and benefits for infants at 32 to 34 weeks' gestation. Until such a dosage is determined, family physicians—in consultation with obstetrician-gynecologists or perinatologists, if local practice patterns dictate—should consider using magnesium sulfate in appropriately selected patients.

Author disclosure: Nothing to disclose.

REFERENCES

1. Crowther CA, Hiller JE, Doyle LW. Magnesium sulphate for preventing preterm birth in threatened preterm labour. Cochrane Database Syst Rev. 2002;(4):CD001060.

2. Grimes DA, Nanda K. Magnesium sulfate tocolysis: time to quit. Obstet Gynecol. 2006;108(4):986–989.

3. Cahill AG, Caughey AB. Magnesium for neuroprophylaxis: fact or fiction? Am J Obstet Gynecol. 2009;200(6):590–594.

4. Doyle LW, Crowther CA, Middleton P, Marret S, Rouse D. Magnesium sulphate for women at risk of preterm birth for neuroprotection of the fetus. Cochrane Database Syst Rev. 2009;(1):CD004661.

5. Rouse DJ. Magnesium sulfate for the prevention of cerebral palsy. Am J Obstet Gynecol. 2009;200(6):610–612.

in reply: I would like to thank Dr. Garrison for his thoughtful letter raising the issue of magnesium sulfate neuroprophylaxis in the context of preterm labor. A recent committee opinion from the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine (ACOG/SMFM)1 also gives tentative support for the use of magnesium sulfate for fetal neuroprotection in preterm labor. I agree with the ACOG/SMFM recommendation that individual centers “develop specific guidelines regarding inclusion criteria, treatment regimens, concurrent tocolysis, and monitoring in accordance with one of the larger trials.”1

Author disclosure: Nothing to disclose.

REFERENCES

1. American College of Obstetricians and Gynecologists Committee on Obstetric Practice; Society for Maternal-Fetal Medicine. Committee Opinion No. 455: Magnesium sulfate before anticipated preterm birth for neuroprotection. Obstet Gynecol. 2010;115(3):669–671.

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