The investigators compared advantages and disadvantages of two forms of noninvasive respiratory support -noninvasive high-frequency oscillatory ventilation (nHFOV) or nasal continuous positive airway pressure (nCPAP) -as a primary mode of ventilation in preterm twins infants with respiratory distress syndrome

Invasive ventilation is related to development of adverse pulmonary and nonpulmonary outcomes in ventilated infants. Various modes of noninvasive respiratory support are being increasingly used to minimize the incidence of bronchopulmonary dysplasia (BPD). The aim of this trial to compare the effects of noninvasive high frequency oscillatory ventilation (NHFOV) and nasal continuous positive airway pressure (NCPAP) in preterm twins infants as the primary mode.

Inclusion Criteria:

1. Gestational age (GA) is from 26 to 37 weeks;
2. Diagnosis of respiratory distress syndrome. The diagnosis of respiratory distress syndrome will be based on clinical manifestations (tachypnea, nasal flaring and or grunting) and chest X-ray findings;
3. Respiratory distress syndrome Silverman score >5;
4. Informed parental consent has been obtained.

Exclusion Criteria:

1. Severe respiratory distress syndrome requiring early intubation according to the American Academy of Pediatrics guidelines for neonatal resuscitation7;
2. Major congenital malformations or complex congenital heart disease;
3. Group B hemolytic streptococcus pneumonia, septicemia, pneumothorax, pulmonary hemorrhage;
4. Cardiopulmonary arrest needing prolonged resuscitation;
5. transferred out of the neonatal intensive care unit without treatment.