Effects of correcting for prematurity on cognitive test scores in childhood

Aims: The American Academy of Pediatrics recommends that test scores should be corrected for prematurity up to 3 years of age, but this practice varies greatly in both clinical and research settings. The aim of this study was to contrast the effects of using chronological age and those of using corrected age on measures of cognitive outcome across childhood.

Methods: A theoretical model was constructed using norms from the Bayley Scales of Infant and Toddler Development, Third Edition; the Wechsler Preschool and Primary Scale of Intelligence, Third Edition Australian; and the Wechsler Intelligence Scales for Children, Fourth Edition Australian. Baseline scores representing different levels of functioning (70, below average; 85, borderline; and 100, average) were recalculated using the normative data for ages 6 months to 16 years to account for 1, 2, 3 and 4 months of prematurity. The model created depicted the difference in standardised scores between chronological and corrected age.

Results: Compared with scores corrected for prematurity, the absolute reduction in scores using chronological age was greater for increasing degree of prematurity, younger ages at assessment and higher baseline scores and was substantial even beyond 3 years of age. However, the pattern was erratic, with considerable fluctuation evident across different ages and baseline scores.

Conclusions: Chronological age results in a lowering of scores at all ages for preterm-born subjects that is greater in the first few years and in those born at earlier gestational ages. Whether or not to correct for prematurity depends upon the context of the assessment.