It is intended to examine the efficacy and safety of intravenous immunoglobulin(IVIG) for the bronchopulmonary dysplasia in preterms. Participants will received continuous infusion IVIG 1 g/kg/day for the first 2 days, 0.5 g/kg/day for next 3 days (total does 3.5 g/kg), repeatable if necessary.

Inclusion Criteria:

• Gestational age between 25 weeks and 29 weeks + 6 days
• Admission within 24 hours after birth.
• Clinical symptoms and chest X-ray results show a highly suspicion of BPD （Clinical symptoms and chest X-ray changes of BPD）.Clinical symptoms develop in several days or weeks after birth, including respiratory symptoms and signs such as shortness of breath, cyanosis or pulmonary rales, intermittent hypoxic attacks, and chronic oxygen dependence (increased oxygen concentration and assisted ventilation) .One of the following signs present in chest X-ray: lung texture thickening or ground glass opacity in early stage, diffuse lung texture blurred, lung hyperinflation, shadow of linear density increased, and shadow of triangular density increased under the pleura.
• A normal full-term newborn without a history of severe lung diseases, birth asphyxia, hypoxic-ischemic encephalopathy or other conditions that may affect the development of the respiratory, nervous and other systems.

Exclusion Criteria:

• Major congenital anomalies(e.g., congenital heart disease, congenital craniocerebral deformity, congenital structural abnormality of respiratory system, congenital hereditary metabolic disease)
• Chromosomal defects (e.g., trisomy 13, 18, 21)
• Severe intracranial hemorrhage
• Multiple organ failure
• With severe lung infections
• Other circumstances that the investigator determines are not suitable for participation in this study