BACKGROUND: Late-onset circulatory collapse (LCC) and bronchopulmonary dysplasia (BPD) are significant complications in extremely preterm infants, leading to adverse short-term outcomes. While adverse short-term outcomes associated with each condition have been reported individually, the impact of the interaction between BPD and LCC on adverse short-term outcomes remains unclear. METHODS: This was a retrospective multicenter cohort study based on the Neonatal Research Network of Japan (NRNJ) including extremely preterm infants weighing <
1500 g who were admitted to the neonatal intensive care unit and registered with NRNJ between 2010 and 2022. Demographic characteristics, morbidity, and mortality were compared among the BPD-LCC-, BPD-LCC+, BPD + LCC-, and BPD + LCC + groups. RESULTS: A total of 14,644 infants were included. LCC was an independent risk factor for BPD (adjusted odds ratio (aOR) 1.30, 95% confidence interval (CI): 1.17-1.46) and significantly increased the risk of more severe BPD forms (aOR 1.34, 95%CI 1.22-1.46). Concomitant LCC in infants with BPD did not affect the incidence of home oxygen therapy and tracheostomy. Furthermore, LCC was found to increase the incidence of periventricular leukomalacia (PVL) (aOR 2.33, 95%CI 1.70-3.18). However, PVL was not associated with BPD. BPD was associated with an increased risk of severe retinopathy of prematurity (ROP) (aOR 1.14, 95% CI 1.02-1.26), which was further increased with concomitant LCC (aOR 1.97, 95% CI 1.71-2.26). CONCLUSIONS: LCC was a risk factor for the development of BPD. Concurrent LCC in infants with BPD increased the risk of severe ROP. Furthermore, LCC increased the incidence of PVL. However, PVL was not associated with BPD. The possible interaction between LCC and BPD was rooted in steroid deficiency. These findings suggest a potential avenue for future preventive interventions.