Comparison of Bayley-2 and Bayley-3 scores at 18 months in term infants following neonatal encephalopathy and therapeutic hypothermia

AIM Neuroprotection trials for neonatal encephalopathy use moderate or severe disability as an outcome, with the Bayley Scales of Infant Development, Second Edition (Bayley-2) Index scores of <70 as part of the criteria. The Bayley Scales of Infant and Toddler, 3rd Development, Third Edition (Bayley-3) have superseded Bayley-2 and yield higher than expected scores in typically developing and high-risk infants. The aim of this study, therefore, was to compare Bayley-2 scores and Bayley-3 scores in term-born infants surviving neonatal encephalopathy treated with hypothermia. METHOD Sixty-one term-born infants (37 males, 24 females; median gestational age at birth 40 wks, range 36-42 wks; median birthweight 3280 g, range 2295-5050) following neonatal encephalopathy and hypothermia had contemporaneous assessment at 18 months using the Bayley-2 and Bayley-3. RESULTS The median Bayley-3 Cognitive Composite score was 7 points higher than the median Bayley-2 Mental Developmental Index (MDI) score and the median Bayley-3 Motor Composite score was 18 points higher than the median Bayley-2 Psychomotor Developmental Index (PDI) score. Ten children had a Bayley-2 MDI of <70; only three children had Bayley-3 combined Cognitive/Language scores of <70. Eleven children had Bayley-2 PDI scores of <70 and four had modified Bayley-3 Motor Composite scores of <70. Applying regression equations to Bayley-3 scores adjusted rates of severe delay to similar proportions found using Bayley-2 scores. INTERPRETATION Fewer children were classified with severe delay using the Bayley-3 than the Bayley-2, which prohibits direct comparison of scores. Increased Bayley-3 cut-off thresholds for classifying severe disability are recommended when comparing studies in this clinical group using Bayley-2 scores.