The aims of this validation study are the testing of the Bernese Pain Scale for Neonates' (BPSN) psychometric properties. The variability of pain reactions related to behavioral and physiological patterns across time will also be examined. Furthermore, the influence of contextual factors on the variability of pain reactions across gestational age groups will be explored. The results will be used for modifications of the BPSN to account for contextual factors in future clinical pain assessment in neonates.