Gould JB, Bennett MV, Phibbs CS, et al. - Experts aspired to explore whether increasing rates and differential uptake of antenatal steroids would bias estimation of the impact of antenatal steroids on neonatal death and severe (grade III-IV) intraventricular hemorrhage (IVH). The sample consisted of infants (n = 28,252) born between 24 and 28 weeks of gestational age in the California Perinatal Quality Care Collaborative. Antenatal steroid exposure rose from 80.1% in 2005 to 90.3% in 2016, severe IVH declined from 14.5% to 9.0%, and mortality dropped from 12.8% to 9.1%. As the proportion of antenatal steroid usage in the population grew, the beneficial effects of antenatal steroids also increased. This apparent increase may be referred to as a "population improvement bias."