Depending on their gestational age, preterm infants need several weeks with different types of breathing-support due to immature development of the lungs, respiratory muscles, chest-wall and respiratory center in the brain. WHO's recommendation on interventions to improve preterm birth outcomes underline the need for more research on respiratory support in infants born preterm. This study will test inter-rater and intra-rater reliability of the Silverman-Andersen Retraction Score, which is a systematic clinical scoring tool for the respiratory work and the severity of respiratory distress in preterm infants. It will examine if there is consistency in the assessments done by doctors and nurses, and also if the observations correlate with technological monitoring. This easy to use scoring tool will help to determine the grade of respiratory distress, to assess respiratory exacerbation, to decide when to start weaning from respiratory support, and to give the best respiratory treatment to the child. This study will contribute to optimize care for preterm infants with respiratory distress.

Inclusion Criteria:

• born <35 weeks gestational age

Exclusion Criteria:

• need of muscle relaxation
• hemodynamic instability

Premature infants born <35 weeks of gestational age. the included infants will be stratified in 3 gestational age groups.