Antenatal corticosteroids for women <34 weeks' gestation at risk of preterm birth within the next 7 days has been the standard of care since the mid 1990s. Historically, there have been insufficient data to support antenatal corticosteroids for women during the late preterm (LPT) period; however, results from a recent multicenter randomized control trial (RCT) found antenatal betamethasone decreased respiratory morbidity in LPT infants (Gyamfi-Bannerman et al., 2016).
The Antenatal Late Preterm Steroids study was a double-blind, placebo-controlled RCT conducted at 17 sites in the United States from 2010 to 2015 (Gyamfi-Bannerman et al., 2016). Participants were 2,831 women with a singleton pregnancy at 34.0 to 36.5 weeks' gestation with a planned birth or at high risk for birth during the LPT period (up to 36.6 weeks). Women were randomized to two injections of betamethasone or a placebo injection 24 hours apart. The primary outcome was a composite reflecting need for respiratory support within 72 hours of birth. Infants born to women in the betamethasone group had a decrease in the primary outcome compared to the placebo group (11.6% vs. 14.4%, P = .02) and had less-severe respiratory morbidity (8.1% vs. 12.1%, P < 0.001). Neonatal hypoglycemia (glucose < 40 mg/dL) occurred more frequently in the betamethasone group (24.0% vs. 15.0%), which may have implications for screening of babies exposed to betamethasone (Gyamfi-Bannerman et al.).
In March 2016, the Society for Maternal-Fetal Medicine (SMFM, 2016) issued a statement encouraging antenatal corticosteroid use for women at risk of LPT birth. Key points are summarized in Table 1. Because 70% of preterm births are LPT (Martin, Hamilton, Osterman, Curtin, & Matthews, 2015), these guidelines can protect LPT babies from respiratory morbidity and enhance perinatal safety and quality.
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