Large variability in performance IQ associated with postnatal morbidity, and reduced verbal IQ among school-aged children born preterm.

Abstract

To assess cognitive ability in a population-based group of prematurely born school-aged children and to relate these findings to postnatal morbidity. The study group consisted of a cohort of 51 children born preterm, 43 (26 boys, 17 girls) of whom were available for psychological evaluation At evaluation, their median age was 10 y (range 8-11 y). They were all born between 1988 and 1991, with gestational age less than 29 wk (median 27, range 24-28). Their median birthweight was 1060g (range 450-1450). The Wechsler Intelligence Scale for Children (WISC-III) was used, and the test results were compared with those of a standardized, age-matched, normative group of children. Thirteen children (30%) performed below average [intelligence quotient (IQ) < 80] for Full Scale IQ (FSIQ). Thirty-six children had a Verbal IQ (VIQ) below the mean value of 100 [84%, 95% confidence interval 73-95%], p < 0.0001. The Performance IQ (PIQ) was within the expected range of a normal population, although a large variability was observed. Discrepancies between VIQ and PIQ of more than 15 IQ units were found in 42% of the children. High postnatal morbidity (days with assisted ventilation, number of blood transfusions) and low birthweight standard deviation scores (SDS) were associated with lower PIQ than VIQ, while low postnatal morbidity and high birthweight were associated with higher PIQ than VIQ. This cohort of preterm children had reduced overall verbal capacity independent of morbidity, and a large variability in performance capacity that was associated with postnatal morbidity. The findings suggest that there are different mechanisms influencing the outcome of verbal and performance capacity in preterm children.