Association between timing of antenatal corticosteroid and developmental outcomes in children born late preterm by high-risk pregnancies

High-risk pregnancies often receive antenatal corticosteroids (ACS) before 34 weeks, even when delivery occurs in the late preterm period. We aimed to evaluate whether the timing of ACS exposure is associated with developmental delay in late preterm infants born to high-risk mothers. We conducted a national, retrospective cohort study of 40,119 singleton late preterm (LPI) live births born in Taiwan between January 1, 2004, and December 31, 2011, followed up until December 31, 2018. We defined high-risk pregnancies based on four clinical conditions: diabetes mellitus, advanced maternal age, hypertensive complications, and cesarean delivery, identified from claims data. The primary outcome is developmental delay (DD). Among 40,119 LPI, 4,730 (11.8%) had exposure to ACS, with the majority (68.4%) exposed to ACS before 34 weeks. Compared to LPT without ACS exposure, those exposed to ACS at 34–36 weeks showed no increased risk of DD (aHR: 0.93[95% CI, 0.80–1.09]), whereas those with ACS before 34 weeks had significantly elevated risk of DD (aHR: 1.12 [95% CI, 1.01–1.24]), especially in infants born to diabetic or older age mothers (aHR: 1.43 [95% CI, 1.13–1.80]; 1.48 [95% CI, 1.11–1.97]). Exposure to ACS at 34–36 weeks was not associated with an increased risk of DD in any high-risk pregnancy subgroup. In contrast, ACS exposure before 34 weeks, particularly among infants born to mothers with diabetes or of advanced maternal age, was associated with a modestly elevated risk. These findings suggest potential susceptibility in specific high-risk groups not previously recognized, underscoring the need for further research.