Very preterm birth poses a long-term risk for social development. The social functioning of very preterm children has been mainly assessed by parents and teachers, although the children’s subjective experience of social functioning may have greater predictive value for well-being in the future. This dissertation is part of the PIPARI study (PIeniPAinoisten RIskilasten käyttäytyminen ja toimintakyky imeväisiästä kouluikään), which follows very preterm-born infants (<32 weeks of gestation and/or birth weight ≤1500g), as well as their healthy controls, from birth onwards. Self-reported loneliness and social competence were evaluated at 11 years of age. This dissertation aimed to identify profiles (Study I) and neurological correlates (Study II) of experienced social functioning in young adolescents born very preterm and term. Furthermore, potential risk factors for social functioning in the very preterm-born group were examined (Studies I, II, and IV).

Most frequently, young adolescents born very preterm reported a profile of average social competence and average level of loneliness. Preterm-born boys reported a profile of low social functioning less frequently than term-born boys, and preterm-born girls reported a profile of high social functioning less often than term-born girls. Social functioning was more frequently associated with brain volumes in the very preterm group than in the term-born group. Higher levels of maternal stress and depression, when the child was from two to four years, associated with lower levels of social functioning in 11-year-old girls born very preterm. Difficulties shifting attention were associated with a higher level of social loneliness in young adolescents born very preterm. Better working memory and better maternal education were associated with heightened social functioning in young adolescents born very preterm. Very preterm birth exerts a longitudinal effect on experienced social functioning, which appears to have neurodevelopmental origins. Female sex, early maternal depression, and difficulties shifting attention may indicate an increased risk of poor social functioning in 11-year-old children born very preterm, whereas high maternal education and better working memory may serve as protective factors.