Publication bias
We evaluated publication bias among the outcome parameters of abdominal distention, NEC, BPD, nasal injury, total oxygen therapy time and the duration of non-invasive ventilation, which was referenced in more than 10 articles. The results suggested that the abdominal distention, nasal injury, total oxygen therapy time and BPD funnel plots we assessed were symmetrical, and the results of Egger’s test were not significant, indicating the absence of publication bias. However, the NEC and duration of the non-invasive ventilation funnel plots were asymmetrical, and Egger’s test showed a significant difference, indicating publication bias ( suppl. eFigs. 7a, 7b, 7c, 7d, 7e, 7f).