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

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.