There was no significant difference among three groups ( all P > @ ) in the following events : respiratory index ( RI ) at @-@ h post-ventilation , abdominal distension , period of non-invasive ventilation , ratio of intubation for invasive ventilation if failed noninvasive ventilation , air-leak syndrome , neonatal necrotizing enterocolitis , periventricular-intraventricular haemorrhage , bronchopulmonary dysplasia , retinopathy of prematurity , mortality rate after @ h of age or rate of abandon for discharge .