Antenatal corticosteroid administration-to-delivery intervals and neonatal outcomes in late preterm labor: a historical cohort study.

BACKGROUND: While antenatal corticosteroids (ACSs) are standard for early preterm birth, their benefit‒risk profile for the late preterm period is controversial, and the effect of the ACS-to-delivery interval on key neonatal morbidities is unclear. This study therefore examined the association between this interval and neonatal outcomes. METHODS: A historical cohort study enrolled 788 singleton pregnancies at 34+ 0 to 36+ 6 weeks of gestation. The non-ACS group comprised women who did not receive ACS. The ACS group was stratified into three subgroups according to the time between the first ACS dose and delivery: less than 2 days, between 2 and 7 days, and more than 7 days. The primary outcome was neonatal respiratory distress syndrome (NRDS), and neonatal hypoglycemia was a key secondary outcome. The associations between newborn outcomes and the intervals between ACS treatment and delivery were examined via multivariable logistic regression. RESULTS: Overall, ACS administration was not associated with reduced NRDS risk. However, this association significantly varied by the administration-to-delivery interval. Compared with the non-ACS group, a significantly lower NRDS risk was observed only in the 2–7 days subgroup [odds ratio (OR) = 0.468, 95% confidence interval (CI): 0.261–0.838, P = 0.011], but not in the < 2 days or > 7 days subgroups (both P > 0.05). In contrast, ACS use was associated with a significantly higher overall risk of neonatal hypoglycemia (OR = 2.594, 95% CI: 1.359–4.951, P = 0.004). This elevated risk was observed in both the < 2 days (OR = 2.922, 95% CI: 1.459–5.853, P = 0.002) and 2–7 days subgroups (OR = 2.641, 95% CI: 1.228–5.681, P = 0.013), but not when the interval exceeded 7 days. For other secondary outcomes, the need for mechanical ventilation was significantly reduced in the 2–7 days group (OR = 0.365, 95% CI: 0.152–0.873, P = 0.024). CONCLUSIONS: In late preterm labor, ACS administration 2–7 days before delivery was associated with a lower risk of NRDS, whereas administration within 7 days was associated with a higher risk of neonatal hypoglycemia. These interval-dependent associations highlight the potential influence of timing on the benefit-risk profile of ACS and indicate the need for prospective validation.