To investigate recent trends in bronchopulmonary dysplasia (BPD) and its risk factors among extremely preterm infants.

Demographic and clinical data were reviewed for 19 370 infants born at 22-27 weeks of gestation registered in the affiliated hospitals of the Neonatal Research Network of Japan between 2003 and 2016. We investigated the overall survival and prevalence of bronchopulmonary dysplasia (BPD) at 36 weeks’ postmenstrual age and risk factors for developing BPD among the survivors.

Among 19 370 infants, 2244 (11.6%) died by 36 weeks' postmenstrual age. The mortality rate decreased from 19.0% (99% CI, 15.7%-22.8%) in 2003 to 8.0% (99% CI, 6.2%-10.3%) in 2016. Among 17 126 survivors, BPD developed in 7792 (45.5%) infants, and its proportion significantly increased from 41.4% (99% CI, 36.5%-46.4%) in 2003 to 52.0% (99% CI, 48.2%-55.9%) in 2016. A multivariable analysis of the survivors showed a positive association of BPD with ≥4 weeks' supplemental oxygen or invasive ventilation, birth weight <750 g, small for gestational age, ≥4 weeks' noninvasive positive pressure ventilation, chorioamnionitis, <26 weeks’ gestational age, <20 cases per year of center patient volume, or treated patent ductus arteriosus. Although the median duration of invasive ventilation was shortened, the proportions of factors associated adversely with BPD generally showed increasing trends over time.

The mortality rate of extremely preterm infants has decreased, but the rate of BPD has increased in survivors between 2003 and 2016. Despite the decreasing duration of invasive ventilation over time, increasing rates of BPD suggest that differences in the patient population or other management strategies influence the development of BPD.