Antenatal corticosteroids and newborn respiratory outcomes in twins: A regression discontinuity study

ObjectiveTo estimate the effect of antenatal corticosteroids on newborn respiratory morbidity in twins.DesignRegression discontinuity applied to population-based birth registry data.SettingBritish Columbia, Canada, 2008-2018.PopulationTwin pregnancies admitted for birth between 31+0 and 36+6 weeks of gestation.MethodsDuring our study period, Canadian clinical practice guidelines recommended antenatal corticosteroid administration for imminent preterm birth up to 33+6 weeks. We used a logistic model to compare the predicted risks of our outcomes among pregnancies admitted for birth immediately before this clinical cut-point (higher probability of exposure to antenatal corticosteroids) versus immediately after it (lower probability).Main outcome measuresOur primary outcome was a composite of newborn respiratory distress or in-hospital death. Our secondary outcome was a composite of newborn respiratory intervention or in-hospital death.ResultsAmong 2524 pregnancies (5035 liveborn twins), 47% of admissions before 34+0 weeks of gestation were exposed to antenatal corticosteroids but only 4.2% of admissions after this cut-point were exposed. The risk of newborn respiratory distress or in-hospital mortality increased abruptly at 34+0 weeks, corresponding to a protective effect of treatment (risk ratio [RR] 0.69, 95% CI 0.53-0.90; risk difference [RD] -12 cases per 100 births, 95% CI -20 to -4.1). There was no clear evidence for or against an effect on newborn respiratory intervention or in-hospital death (RR 0.89, 95% CI 0.70-1.13; RD -4.2 per 100, 95% CI -13 to +4.2).ConclusionsOur findings provide evidence for the effectiveness of antenatal corticosteroids in preventing adverse newborn respiratory outcomes in twins.