UNLABELLED: Although the administration of antenatal corticosteroids (ACS) is generally recognized as cost-effective and beneficial, recent studies have indicated potential long-term adverse effects on neurodevelopment, particularly for term-born infants. However, limited research has explored the association between the timing of ACS exposure, gestational age (GA) at birth, and their potential implications for mental and behavioral outcomes in offspring compared to non-exposed infants. This study aimed to examine the association between the timing of antenatal corticosteroid (ACS) exposure for threatened preterm labor and childhood mental disorders among early-term and full-term births. All eligible term infants born between 2010 to 2014 were included in this nationwide study and followed until the end of 2021. The primary outcome was any childhood mentaldisorders, with secondary outcomes being attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD), and developmental delay (DD). Compared to unexposed infants, ACS exposure before 34 weeks of GA increased the risk of developing mental behavior disorders. Exposure to ACS before 34 weeks was significantly associated with an increased risk of ADHD and DD
however, this association was observed only in early-term births but not in those born at full-term. CONCLUSION: Our finding suggests a need for further investigation into the influence of GA at birth on these disorders and supports that the risk of childhood mental disorders in term infants varied among different ACS exposure timing. WHAT IS KNOWN: • While administration of antenatal corticosteroids (ACS) for preterm birth threats is widely acknowledged as both cost-effective and beneficial, recent studies have raised concerns about potential long-term adverse effects on neurodevelopment, particularly in term-born infants. • Previous studies have found that early-term birth is associated with lower intelligence, ADHD, and poorer school performance compared to full-term birth. WHAT IS NEW: • There is an interaction between the timing of ACS treatment and gestational age at birth with respect to the likelihood of neurodevelopmental outcomes in term-born infants. • Exposure to ACS before 34 weeks is associated with an increased risk of any childhood mental disorders, specifically ADHD and DD, among early-term births, whereas this association was not observed in infants who reached full-term gestation.