Prenatal corticosteroid prophylaxis for women delivering at late preterm gestation

Despite overwhelming evidence regarding the benefits of prenatal corticosteroid prophylaxis, many women delivering at preterm gestation did not receive this therapy in the early 1990s, possibly because some concerns regarding the efficacy and safety of corticosteroid use. The National Institutes of Health Consensus Development Conference in 1994 addressed these issues and strongly endorsed the use of a single course of prenatal corticosteroid therapy for women at risk of preterm delivery between 24 and 34 weeks of gestation. A Cochrane review provided further evidence supporting this therapeutic strategy, showing significant reductions in rates of neonatal death, respiratory distress syndrome (RDS), cerebroventricular hemorrhage, necrotizing enterocolitis, infectious morbidity, need for respiratory support, and NICU admission with corticosteroid prophylaxis.
However, in clinical practice, prenatal corticosteroid prophylaxis is often targeted to women at risk of preterm delivery up to 32 weeks of gestation, possibly because alternative interpretations of the National Institutes of Health Consensus Conference recommendations. Moreover, prenatal corticosteroid prophylaxis for women at risk of preterm birth at 33 and 34 weeks of gestation may increase rates of late preterm birth with higher incidence of mortality and morbidity compared with term infants.
An American group has conducted a study to determine gestational age-specific patterns of prenatal corticosteroid use, RDS, and infant mortality resulting from RDS, with a focus on live births at 33 to 36 weeks of gestation.
Data on all live births in the United States (years 1989–1991, 1995–1997, 2002–2004) and Nova Scotia, Canada (years 1988–2007) were used. Gestational age-specific temporal trends in infant deaths resulting from RDS were quantified in the US, and gestational age-specific temporal trends in corticosteroid use and morbidity were quantified in Nova Scotia.
In the US, infant deaths associated with RDS decreased by 48% from 1989–1991 to 1995–1997 and then decreased by another 18% by 2002–2004. The latter mortality reduction was evident at 28 to 32 weeks but not 33 to 36 weeks of gestation. Corticosteroid use at 28 to 32 weeks was high in Nova Scotia and increased from 30.7% in 1988–1989 to 52.9% in 2006–2007, whereas rates of use at 33 to 36 weeks were much lower. Increased corticosteroid use at 33 and 34 weeks was estimated to reduce RDS.
Overall, increasing use of preterm labor induction and cesarean delivery have enhanced rates of preterm birth at 33 to 36 weeks of gestation. Infants at 33 and 34 weeks of gestation have not been optimally targeted to receive prenatal corticosteroid prophylaxis; this failure seems to have been at least partly responsible for the absence of a reduction in infant deaths associated with RDS between 1995–1997 and 2002–2004. On these basis, clinicians should reconsider practices with regard to prenatal steroid prophylaxis among women at risk for preterm birth at 33 and 34 weeks of gestation.

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