Clinical Review

How to manage emergencies associated with tocolysis for preterm labor

OBG Manag. 2013 July;25(7):46-52

Cornelia R. Graves, MD
Dr. Graves is Medical Director, Tennessee Maternal Fetal Medicine; Medical Director for Perinatal Services at Baptist Hospital; and Clinical Professor at Vanderbilt University in Nashville, Tennessee.

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References

1. McPheeters ML, Miller WC, Hartman KE, et al. The epidemioloy of threatened preterm labor: a prospective cohort study. Am J Obstet Gynecol. 2005;192(4):1325–1330.

2. American Congress of Obstetrics and Gynecology. ACOG Practice Bulletin No. 127: Management of preterm labor. Obstet Gynecol. 2012;119(6):1308–1317.

3. Gross G, Imamura T, Vogt SK, et al. Inhibition of cyclooxygenase-2 prevents inflammation mediated preterm labor in the mouse. Am J Physiol Pegul Intergr Comp Physiol. 2000;278(6):R1415–R1423.

4. Gyetvai K, Hannah ME, Hodnett ED, Ohlsson A. Tocolytics for preterm labor: a systematic review. Obstet Gynecol. 1999;94(5 Pt 2):869–877.

5. Macones GA, Bader TJ, Asch DA. Optimising maternal-fetal outcomes in preterm labour: a decision analysis. Br J Obstet Gynaecol. 1998;105(5):541–550.

6. McPheeters ML, Miller WC, Hartmann KE, et al. The epidemiology of threatened preterm labor: a prospective cohort study. Am J Obstet Gynecol. 2005;192(4):1325–1330.

7. Nanda K, Cook LA, Gallo MF, Grimes DA. Terbutaline pump maintenance therapy after threatened preterm labor for preventing preterm birth. Cochrane Database Sys Rev. 2002;(4):CD003933.

8. Rouse DJ, Hirtz DG, Thom ED, et al; Eunice Kennedy Shriver NICHD Maternal-Fetal Medicine Units Network. A randomized controlled trial of magnesium sulfate for the prevention of cerebral palsy. N Engl J Med. 2008;359(9):895–905.

9. US Food and Drug Administration. Terbutaline: Label Change—Warnings Against Use for Treatment of Preterm Labor. Published February 17, 2011. http://www.fda.gov/Safety/MedWatch/SafetyInformation/SafetyalertsforHumanMedicalProducts/ucm243843.htm. Accessed June 17, 2013.

10. Vermillion ST, Scardo JA, Lashus AG, Wiles HB. The effect of indomethacin tocolysis on fetal ductus arteriosus constriction with advancing gestational age. Am J Obstet Gynecol. 1997;177(2):256–259.

11. Wu QA, Ye YQ. Neuromuscular blockade after therapy with magnesium sulfate and amlodipine. Eur J Obstet Gynecol Reprod Biol. 2010;149(2):225.

12. US Food and Drug Administration. Magnesium Sulfate: Drug Safety Communication—Recommendation against Prolonged Use in Preterm Labor. Published May 30, 2013. http://www.fda.gov/Safety/MedWatch/SafetyInformation/SafetyAlertsforHumanMedicalProducts/ucm354603.htm. Accessed June 17, 2013.

In May 2013, the FDA issued a warning about the risk of neonatal complications with long-term maternal magnesium administration. These complications include osteopenia, low calcium, and bone fracture. The pregnancy category for magnesium sulfate will be changed from “A” to “D” because of these teratogenic effects.¹²

CASE 4 Resolved

Because magnesium is mainly cleared by renal excretion, the clinician administers the medication with caution in this patient with reduced renal function. The clinician administers the same 4- to 6-g bolus that would be given a patient with normal kidney function, but the maintenance dose is reduced to 1 g. Magnesium levels are obtained every 12 hours or when clinically indicated.

Bottom line: Be ready to act

The short-term use of tocolytic therapy usually is not associated with maternal or fetal complications. After initial administration, maintenance tocolytic therapy probably does not prolong gestation.

Given the potential for harm without additional fetal benefit associated with extended therapy, I recommend that clinicians follow current clinical guidelines from ACOG for use of tocolytic agents. In the process, be vigilant for complications and be ready to act appropriately. Keep maternal and fetal conditions in mind when selecting a tocolytic agent.