2.1 Study Design
We performed a retrospective chart review of infants born with a body weight less than 1000 g and admitted to National Cheng Kung University Hospital from July 2014 to June 2020. We enrolled infants who received PDA invasive management involving either surgical ligation or transcatheter occlusion and were diagnosed with BPD at 36 weeks’ post-menstrual age. Infants with BPD severity already classified before the procedure were excluded. According to the NICHD 2001 BPD diagnosis criteria, BPD was considered as 28 cumulative days of supplemental oxygen more than 21%. The severity of BPD was defined according to a previously published definition (Supplementary Table 1).16 Based on the type of intervention, patients were divided into a surgical ligation group (Group A) or a transcatheter occlusion group (Group B). The study protocol was approved by the Institutional Review Board (protocol code A-ER-109-137) of this institution.