Longitudinal studies of executive and cognitive development after preterm birth

The population of survivors after preterm birth is increasing, and, in conjunction with this, there is growing concern about their long-term development. Stockholm Neonatal Project (SNP) is a longitudinal population-based study of children born prematurely in 1988-93, with a very low birth weight (<1500 g), who have been followed prospectively from birth through adolescence. A matched control group was recruited at age 5 1⁄2 years. The overall aim of this thesis was to investigate the long-term development of preterm children compared to controls, paying particular attention to their executive functions (EF) in relation to the degree of prematurity, birth weight and medical risks. Study I, utilizing Bender drawings and other data obtained at age 5 1⁄2 years, showed a disadvantage in visuo-motor development in preterm children, especially among the boys. Visuo-motor skills were highly related to performance IQ (PIQ) in both groups, and also to EF in the preterm group. In Study II, data from the NEPSY test battery administered at age 5 1⁄2 was used, and neuropsychological profiles typical of preterm children and term born children respectively, were identified through cluster analysis. The general level of performance corresponded well with intelligence, motor functions and parental education in both groups, but preterm children had overall lower results and exhibited greater variability across domains. Study III showed that extremely preterm birth (w. 23-27) per se poses a risk for cognitive outcome at age 18, particularly for EF, and that perinatal medical complications add to the risk. By contrast, adolescents born very preterm (w. 28-31) performed just as well as term-born controls in all cognitive domains. However, adolescents who had been born moderately preterm (w. 32-36) and small for gestational age, showed general cognitive deficits. Study IV found that cognitive development was highly stable over time, with parental education and EF at 5 1⁄2 years being significant predictors for cognitive outcome at age 18, in both groups. In the preterm group, perinatal medical risks and being small for gestational age continued to significantly influence development from 5 1⁄2 to 18 years. Study V demonstrated that neuropsychological scoring of Bender drawings, which was developed in study I, predicted general cognitive outcome as well as EF in adolescence. This indicates that developmental screening using Bender drawings with neuropsychological scoring may be useful around school entry. In summary, the results illustrate that cognitive outcome after preterm birth is highly diverse and influenced by biological and environmental factors. No single factor can explain or predict children’s development, but we conclude that extreme prematurity presents a particular risk for EF dysfunction. Developmental screening is recommended to identify children who may benefit from special educational interventions.