Antenatal steroid therapy is standard care for women at imminent risk of preterm delivery.

When deliveries occur within 7 days of treatment, antenatal steroid therapy reduces the risk of neonatal death and improves preterm outcomes by exerting diverse developmental effects on the fetal organs, in particular the preterm lung and cardiovascular system.

There is, however, sizable variability in antenatal steroid treatment efficacy, and an important percentage of fetuses exposed to antenatal steroid therapy do not respond sufficiently to derive benefit.

Respiratory distress syndrome, for example, is a central metric of clinical trials to assess antenatal steroid outcomes. In the present analysis, we addressed the concept of antenatal steroid nonresponsiveness, and defined a failed or suboptimal response to antenatal steroids as death or a diagnosis of respiratory distress syndrome following treatment.