To investigate the hematological features of infants with bronchopulmonary dysplasia (BPD) and their relationships with clinical severity.

This prospective observational study enrolled 73 BPD patients from a total of 331 infants with a birth weight of <1500 g from 2005 to 2013.

The clinical severity of BPD was defined by the duration of oxygen supplementation and positive pressure ventilation (PPV) in line with the diagnostic criteria of BPD. The hematological status and cytokine levels were surveyed from blood samples at birth and at 2 and 4 weeks of life.