Executive Function at Early School Age in Children Born Very Preterm
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy (PhD)
Impairments in executive function have been posited to account for some of the poor cognitive and educational outcomes associated with very preterm birth. As part of a prospective, longitudinal study, this research examined executive function in a regionally representative sample of 103 children born very preterm and/or very low birth weight (<33 weeks GA / <1500g) and a comparison sample of 108 full term children at age 6 years (corrected for prematurity). The specific aims of the study were 1) to describe the performance of children born very preterm and full term on a range of executive function measures, 2) to identify the antecedent medical, neurological and socio-familial factors associated with executive function performance within the very preterm group, and 3) to examine linkages between children’s executive function performance and their academic achievement at age 6 years. Children underwent a comprehensive developmental assessment, including standardised tests of IQ and academic achievement in mathematics, reading and receptive language. Additionally, they completed a number of executive function tasks selected to assess verbal working memory (Digit Span), spatial working memory (Corsi Blocks), planning and problem-solving (Tower of Hanoi), selective attention (Visual Search), shifting and inhibitory control (Detour Reaching Box) and sustained attention and inhibition (Kiddie-Conner’s Continuous Performance Task; K-CPT). Parents and teachers of these children also completed the Behavioural Rating Inventory of Executive Function and teachers rated children’s performance in reading, arithmetic and comprehension in relation to their classroom peers. Results revealed a pervasive pattern of impairment across multiple measures of executive function in children born very preterm relative to their full term peers. Specifically, children born very preterm were less likely to be able to complete any backward Digit Span trials (p<0.05) and showed lower raw scores on this task (p<0.1) than children in the full term group. Children born very preterm showed lower spatial span scores on the Corsi Blocks Task (p<0.01). They also showed lower planning performance, as assessed by the Tower of Hanoi (p<0.05). Children born very preterm made more inhibitory control/shift errors on the Detour Reaching Box and demonstrated less accuracy in their Visual Search (p<0.001) than children born full term. Finally, they showed lower levels of sustained attention on the K-CPT (p<0.001). Parents, teachers and examiners rated these children as having greater difficulties across multiple areas of executive function. These differences remained significant after controlling for group differences in socioeconomic status and after exclusion of children with severe cognitive and motor impairments. Within the very preterm group, antecedent predictors of poorer working memory and planning performance included male gender (p<0.001), intrauterine infection (p<0.05) and severity of cerebral white matter abnormality on term-equivalent MRI (p<0.05). Lower gestational age (p<0.05) and male gender (p<0.001) were related to poorer executive attention performance. Familial predictors of poorer executive performance included instability in parenting (p<0.05), higher levels of parental intrusiveness (p<0.1) and lower levels of interactional synchrony (p<0.05) between parent and child, recorded at earlier follow-up points. Finally, children’s executive function performance was highly correlated with school achievement in reading, arithmetic and language comprehension (p<0.001). Findings suggest a global pattern of executive impairment amongst children born very preterm, with these difficulties placing children at risk for poor academic performance and learning difficulties. Findings also suggest that both neurological pathology and early parenting experiences are important mediators of the relationship between very preterm birth and poor executive function, highlighting the importance of these areas for early intervention.