NPPB and bronchopulmonary dysplasia: When the natural logarithm of the serum NT-ProBNP level increased by 1 unit on the 7th day (±2 days), the risk of moderate-to-severe BPD/death was the highest (OR = 3.753; 95%CI: 2.984~4.720; P < 0.001; Table 2), and the predictive ability was the strongest.