Impact of antenatal corticosteroids-to-delivery interval on very preterm neonatal outcomes: a retrospective study in two tertiary centers in Japan

Background Antenatal corticosteroids (ACS) are administered to prevent neonatal complications and death in women at risk of imminent preterm birth. Internationally, the optimal interval from ACS to delivery (ACS-to-delivery interval) is within seven days; however, evidence in Asian populations specifically is limited. This study aimed to investigate the association between ACS-to-delivery interval and the incidence of neonatal complications in Japan. Methods This retrospective observational study enrolled singleton neonates born preterm at < 32 weeks of gestational age between 2012 and 2020 at two tertiary centers. A total of 625 neonates were divided into the following four groups according to the timing of ACS (measured in days): no ACS (n = 145), partial ACS (n = 85), ACS 1-7 (n = 307), and ACS >= 8 (n = 88). The following outcomes were compared between the groups: treated respiratory distress syndrome (RDS), severe intraventricular hemorrhage (IVH), treated patent ductus arteriosus (PDA), necrotizing enterocolitis, sepsis, bronchopulmonary dysplasia (BPD), treated retinopathy of prematurity (ROP), periventricular leukomalacia, and death discharge. Results The ACS 1-7 group had significantly decreased adjusted odds ratios (ORs) for treated RDS (0.37 [95% confidence interval: 0.23, 0.57]), severe IVH (0.21 [0.07, 0.63]), treated PDA (0.47 [0.29, 0.75]), and treated ROP (0.50 [0.25, 0.99]) compared with the no ACS group. The ACS >= 8 group also showed significantly reduced adjusted ORs for RDS (0.37 [0.20, 0.66]) and treated PDA (0.48 [0.25, 0.91]) compared with the no ACS group. However, the adjusted ORs for BPD significantly increased in both the ACS 1-7 (1.86 [1.06, 3.28]) and ACS >= 8 groups (2.94 [1.43, 6.05]) compared to the no ACS group. Conclusions An ACS-to-delivery interval of 1-7 days achieved the lowest incidence of several complications in preterm neonates born at < 32 weeks of gestational age. Some of the favorable effects of ACS seem to continue even beyond >= 8 days from administration. In contrast, ACS might be associated with an increased incidence of BPD, which was most likely to be prominent in neonates delivered >= 8 days after receiving ACS. Based on these findings, the duration of the effect of ACS on neonatal complications should be studied further.