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 The Bayley Scales of Infant and Toddler, 3rd Development, Third Edition (Bayley-3) have superseded Bayley-2 and yield higher than expected scores in typically developing and high-risk infants.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.