Understanding the comfort or discomfort expressions of preterm and term newborns represents a challenge for both parents and nurses, particularly in hospitalization settings. While parents rely mainly on intuitive parenting abilities and parental experience, pediatric nurses receive specific training to recognize newborns' expressions. This study compared the perception of preterm and term infants' facial emotion expressions across five observer groups: 63 parents of hospitalized preterm infants, 53 parents of hospitalized term infants, 55 general parents, 91 naïve non-parents and 61 professional pediatric nurses (total N = 323). Observers from Strasbourg (France) and Geneva (Switzerland) rated 30 video extracts of preterm infants at 32- and 40-weeks PMA and of term infants, balanced across positive, negative, and neutral conditions. They judged the comfort, discomfort, or neutrality of expressions using a graduated scale. The objective was to assess the influence of training, professional, and parental experience on evaluations of newborns' emotional expressions. The effect of parenting emerges in valence judgement, with parents and non-parents' tendency to attribute discomfort to the newborn's expression, and nurses being more likely than all other groups to judge infant expressions as comfort. Across groups, preterm infants at 32 weeks were mainly perceived as uncomfortable, but ratings shifted toward comfort at 40 weeks, while term infants showed a more balanced profile. Finally, accuracy analyses showed that nurses were most accurate in recognizing comfort, parents performed best for discomfort, and non-parents achieved the highest accuracy for neutral expressions, with significant contrasts across all groups (p < .05). These findings highlight that the recognizability of infant emotional expressions depends on the infants' developmental maturation, while the accuracy and interpretive patterns of ratings are shaped by the observers' parental or professional experience.