Antenatal Corticosteroid Administration and Childhood Respiratory Morbidity: A Regression Discontinuity Study.

Objective: To determine if routine administration of antenatal corticosteroids affects the risk of infant lower respiratory tract infection and/or childhood asthma.

Design: Linked population-based cohort analysed using a regression discontinuity design, which better controls for confounding than standard observational studies.

Setting: British Columbia, Canada.

Population: Singleton pregnancies with a maternal admission for delivery between 31 + 0 and 36 + 6 weeks' gestation from 2000 to 2016, with follow-up to 2020.

Methods: We estimated if risks of childhood respiratory outcomes differed between pregnancies admitted just before the Canadian recommended clinical cut-off for antenatal corticosteroid administration of 34 + 0 weeks gestation (i.e., with higher probability of exposure to antenatal corticosteroids; 'exposed') than those admitted just after this cut-off (i.e., with lower probability of exposure; 'unexposed') using log binomial regression (infant lower respiratory infection hospitalisation) and pooled log binomial regression (asthma).

Main outcome measures: Infant lower respiratory tract infection hospitalisation, inpatient or outpatient asthma diagnosis at 1-18 years.

Results: In our cohort of 21 965 children, 412 (1.9%) infants were hospitalised with a lower respiratory tract infection and 2287 (10.4%) were diagnosed with asthma. Routine administration of antenatal corticosteroids was not associated with infant lower respiratory tract infection (risk ratio = 0.95 [95% CI: 0.61, 1.37], risk difference = -0.15 excess cases per 100 [95% CI: -1.30, 0.99]) or childhood asthma (rate ratio = 1.08 [95% CI: 0.88, 1.24] 5.49 excess cases per 100 by age 13 years [95% CI: -1.78, 14.39]).

Conclusions: We found no evidence that routine administration of antenatal corticosteroids affects the risk of later childhood respiratory illnesses.