Inclusion Criteria:  In-born infants at 25+0-29+6 weeks of gestational age Spontaneously breathing at birth but requiring noninvasive respiratory support with nCPAP at a pressure of 6-8 cmH2O to maintain an SpO2 between 90% and 95%. Parental consent has been obtained Exclusion of causes of respiratory failure other than RDS  Exclusion Criteria:  Endotracheal intubation in the delivery room for resuscitation or insufficient respiratory drive according to European guidelines Prolonged premature rupture of membranes (PROM) for more than 3 days Presence of major congenital malformations or chromosomal anomalies Hydrops fetalis Inherited disorders of metabolism Administration of surfactant before performing the LUS. Other respiratory diseases than RDS