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

Abstract Objective To estimate the effect of antenatal corticosteroids on newborn respiratory morbidity in twins. Design Regression discontinuity applied to population‐based birth registry data. Setting British Columbia, Canada, 2008–2018. Population Twin pregnancies admitted for birth between 31 +0 and 36 +6 weeks of gestation. Methods During 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 measures Our 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. Results Among 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). Conclusions Our findings provide evidence for the effectiveness of antenatal corticosteroids in preventing adverse newborn respiratory outcomes in twins.