NPPB and bronchopulmonary dysplasia: In addition, our previous research found the role of NT-proBNP levels on the 7th day in predicting BPD and the severity of BPD (30), so we planned to further explore the relationship between NT-proBNP level on the 7th day and PLS, which might lay a foundation for future studies on the NT-proBNP level on 7th day as an early predictor of length of stay.