It is intended to examine the short-term and long-term efficacy and safety of intravenous immunoglobulin(IVIG) for the bronchopulmonary dysplasia in preterms born at 28 weeks and below. 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 ≤ 28 weeks + 6 days
• Admission within 24 hours after birth.
• Infants show a suspicion of BPD, the diagnosis is suspected based on the following clinical manifestations and chest X-ray findings.

Clinical manifestations: Respiratory symptoms such as tachypnea (rapid breathing) and cyanosis, requiring respiratory support (including invasive, non-invasive, or oxygen therapy) to maintain oxygen saturation.

Chest X-ray: Findings include increased bilateral lung markings or ground-glass opacities, and diffuse increased density in both lungs. Other possible causes such as infection or heart disease should be ruled out.

• 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