The effects of a preterm labor episode prior to 34 weeks are evident in late preterm outcomes, despite the administration of betamethasone

Objective: We sought to assess whether betamethasone (BETA) <34 weeks reduces adverse outcomes in late preterm infants. Study Design: We performed a retrospective cohort study of patients with spontaneous birth 34-36 6/7 weeks. We determined whether patients were exposed to preterm labor (PTL) <34 weeks and BETA and calculated the incidence of adverse respiratory and composite outcomes and neonatal intensive care unit admission. We used χ² analyses to determine associations between PTL+BETA and adverse outcomes, and Poisson regression to model cumulative incidence and control for confounders. Results: We enrolled 700 mother-infant pairs. The 36-week PTL+BETA infants were at increased risk of respiratory outcome (incident risk ratio [IRR], 2.73; 95% confidence interval [CI], 1.37-5.45), neonatal intensive care unit admission (IRR, 2.01; 95% CI, 1.14-3.56), and composite outcome (IRR, 1.70; 95% CI, 1.08-2.68) compared to those without PTL+BETA. Chorioamnionitis was independently associated with all adverse outcomes. Conclusion: We hypothesize that early PTL is a surrogate for intrauterine inflammation and is responsible for the observed adverse outcomes in those with PTL+BETA.