Executive functioning profile of a national cohort of adults born very low birthweight.

Abstract

Introduction. Increasing evidence shows that children born very preterm (<33 weeks; VPT) and/or very low birthweight (<1500g; VLBW) are at high risk for neurodevelopmental difficulties across a range of domains. One of the most common adverse outcomes in this population is cognitive or intellectual impairment however, due to the broad nature of this outcome, there has been increasing interest in identifying specific areas of cognitive impairment. This has led to research examining EF (executive function). To date studies have almost exclusively examined EF difficulties in children and, to a lesser extent, in adolescents born VPT/VLBW. Very few studies have examined whether earlier observed EF impairments in these individuals persist into adulthood. Accordingly, the aim of this thesis was to compare performance of adults born VLBW and full term (FT) on a series of tasks across three key domains of EF: inhibitory control, working memory and cognitive flexibility. Secondary aims were to examine the extent to which between-group differences in EF may be affected by processing speed and the extent to which decreasing birthweight impacts on EF performance.

Research Methods. All infants born VLBW in New Zealand during 1986 were enrolled in a study of acute retinopathy of prematurity (n=413) and followed prospectively from birth to age 26-30 years. At 26-30 years (M=28.5), 229 participants (77% of survivors) and 100 age-matched FT born adults (M=28.2) underwent a comprehensive neuropsychological assessment as part of a two-day evaluation. Participants completed five EF tasks. These included: inhibitory control (Hayling Sentence Completion Test), visuospatial working memory (computerized Sternberg-based task), auditory-verbal working memory (Elevator Counting subtests from the Test of Everyday Attention) and cognitive flexibility (Comprehensive Trail Making Test [CTMT] and the Brixton Spatial Anticipation Test). The Symbol Digit Modalities Test (SDMT) provided a measure of processing speed.

Results. Findings revealed a pervasive pattern of impairment across multiple measures of EF in adults born VLBW relative to FT controls. Specifically, adults born VLBW performed significantly poorer on measures of inhibitory control, visuospatial working memory, cognitive flexibility and on one of the auditory-verbal working memory tests (p<.001). Consistent with these findings, rates of EF impairment were also significantly higher (OR range 2.10 – 7.37) among VLBW adults relative to the control group. Adjusting for the effects of processing speed attenuated the between-group differences in EF performance; however, for most tasks differences remained statistically significant. A linear association was evident between birthweight and EF performance (p<.001), suggesting a higher risk of impairment on EF tasks with decreasing birthweight. A confirmatory factor analysis performed with the task measures supported a single factor model of EF.

Discussion. At age 28 years, adults born VLBW perform worse than control adults on EF tasks across various domains. The findings suggest that while EF difficulties can be explained in part by processing speed, in large the differences indicate a global pattern of EF impairment that places VLBW individuals at higher risk of difficulties for everyday functioning. These findings emphasize the importance of appropriate intervention strategies in the early childhood years to mitigate the potential impact of EF impairments on later life course opportunities in adulthood. With appropriate intervention and supports in adulthood, some EF skills could be malleable to change however, continuing to research intervention opportunities and EF outcomes in later adulthood, could help to ensure that a high quality of life follows for individuals born VLBW.