Abstract: Objective To explore the risk factors affecting the severity of bronchopulmonary dysplasia(BPD) in very and extremely preterm infants in neonatal intensive care unit(NICU), and to provide theoretical evidence for the prevention and treatment of different degrees of BPD.Methods The research method of retrospective analysis was applied. The clinical data of 129 very and extremely preterm infants with  gestational age <32 weeks diagnosed with BPD in neonatal intensive care unit of our hospital from December 2013 to December 2018 were collected, and the infants were divided into grade Ⅰ BPD(33 cases),grade Ⅱ BPD(55 cases) and grade Ⅲ BPD(41 cases) according to the clinical diagnostic criteria. Univariate analysis was used to compare the maternal status, birth status, complications and treatment measures. To explore the independent risk factors influencing the severity of bronchopulmonary dysplasia in very and extremely preterm infants, multivariate Logistic regression analysis was used to analyze the significant factors of univariate analysis．Results Univariate analysis showed that there were statistically significant difference in birth weight, pulmonary hemorrhage, extrauterine growth retardation,  oxygen inhalation concentration >40%, blood transfusion ≥3 times, high frequency invasive mechanical ventilation and invasive mechanical ventilation time among the three groups. Multivariate Logistic regression analysis showed that pulmonary hemorrhage（OR=9.207,95%CI：0.151～4.289） and invasive mechanical ventilation time （OR=1.110,95%CI：0.021～0.188） were independent risk factors for BPD severity in very and extremely preterm infants.Conclusion The severity of BPD in very and extremely preterm infants is related to multiple factors. Pulmonary hemorrhage and invasive mechanical ventilation time are independent risk factors for BPD severity in very and extremely preterm infants. Prevention of pulmonary hemorrhage and reduction of invasive mechanical ventilation time are important measures to reduce the severity of BPD.

Key words: Bronchopulmonary dysplasia, Severity, Very premature infants, Extremely premature infants, Risk factors