Antenatal Corticosteroids and Risk of Cerebral Palsy: A Regression Discontinuity Study

To use a natural experiment to investigate the effect of antenatal corticosteroids on the risk of cerebral palsy.

We included singleton livebirths with a maternal admission for delivery from 31 + 0 through 36 + 6 weeks of gestation, in British Columbia, Canada, between 2000 and 2015. Guidelines recommended antenatal corticosteroids through 33 + 6 weeks, and we estimated the effect of the corresponding sharp drop in the proportion treated at 34 + 0 weeks on the risk of a composite of death before age 2 or cerebral palsy. We defined cerebral palsy using diagnostic codes in hospital and physician-billing records before age 5 years and corrected for misclassification using external estimates of the sensitivity and specificity. We used logistic regression to estimate marginal effects at 34 + 0 weeks.

There were 20 009 children in our study sample. The crude and misclassification-corrected risks of cerebral palsy were 6.2 and 5.6 per 1000, respectively. The risk of death before age 2 or cerebral palsy declined with increasing gestational age at maternal admission for delivery, but we found no convincing evidence of an abrupt change just before vs just after 34 + 0 weeks (risk ratio: 0.98, 95% confidence interval: 0.50 to 1.98). Results were similar using a composite outcome of in-hospital newborn death or cerebral palsy, and using cerebral palsy alone.

We did not find evidence that the lower likelihood of being treated with antenatal corticosteroid at 34 + 0 weeks affected the risk of cerebral palsy, but the estimates were imprecise and compatible with benefits or harms.