Objective: Research has shown that premature birth poses a risk for later cognitive development, particularly in the executive domain, but few studies extend beyond the early school years. Adolescence is a critical period for cognitive maturation, and this study investigated the cognitive outcome in a Swedish cohort of prematurely born 18-year olds, in relation to gestational age at birth and medical risks in the perinatal period.
Participants and Methods: As part of Stockholm Neonatal Project, 134 adolescents born preterm with very low birth weight (< 1500g) and 94 matched controls born at term, participated in a follow-up study at age 18. General intelligence, as well as executive, memory, language and visual motor functions were measured by WISC-III, Delis-Kaplan Executive Function System, naming tests, Rey Auditory Verbal Learning test, face recognition, and Visual Motor Integration test.
Results: Extremely preterm adolescents (EPT, GA 23-27, n=74) performed worse than adolescents born either very preterm or at term, on all cognitive tasks and particularly on executive measures. 50% of the EPT group had suffered perinatal medical complications, and had more pervasive cognitive deficits than EPTs with low medical risk. By contrast, very preterm adolescents (GA 28-31; n=36) performed consistently on a par with the controls. Moderately preterm with very low birth weight (GA 32-36; n=25), who had experienced varying degrees of intrauterine growth retardation, tended to score lower than very preterm and control adolescents, particularly on complex cognitive measures.
Conclusions: Extremely preterm birth per se poses a risk for long-term cognitive outcome, particularly in executive functions. These risks may be exacerbated by medical complications. Children born after 28 weeks of gestation or later, with normal birth weight and no perinatal complications, do not have an elevated risk for cognitive deficits at age 18.