Presented at the Neonatal Society 2012 Autumn Meeting.
Jary S1, Whitelaw A1, Walloeb L2, Thoresen M1,2
1 Neonatal Neuroscience, School of Clinical Science, University of Bristol, Bristol, UK
2 Department of Physiology, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
Background: Clinical trials of neuroprotection for infants with moderate or severe neonatal encephalopathy (NE) have used death or severe disability as trial outcomes with Bayley Scales of Infant Development-2 Index (1) scores <70 as part of criteria for severe disability (2). Bayley-3 (3) has now replaced Bayley-2 and, in preterm infants, is reported to give higher scores than Bayley-2 (4,5). Term infants with NE have a different spectrum of neurodevelopment (6,7) as all have brain injury. We hypothesised that fewer infants would have scores <70 using Bayley-3 than with Bayley-2. If so, this could confuse interpretation of new neonatal trials of NE and historical comparisons. Our aims were to prospectively compare Bayley-2 with corresponding scores in Bayley-3; to investigate the cut-off thresholds for moderate and severe disability in both tests and to derive conversion algorithms to predict Bayley-2 scores from Bayley-3 scores in a well-defined cohort of infants following NE.
Methods: Study participants were 61 children born 2007-2010 who fulfilled the entry criteria for therapeutic hypothermia (TH) and for whom complete scores for both Bayley-2 and Bayley-3 were available. Assessment was at median age 18.3 (16.8-19.7) months in a single session by one assessor proficient in the administration of both versions of the test. Bayley-3 scales were administered with any extra items specific to Bayley-2 interspersed as judged appropriate for the individual child to maximise motivation and minimise fatigue. Items with differences in administration were presented in accordance with Bayley-3 instructions but scored according to instructions of each version of the test. Inter-scorer reliability, investigated in 10 infants from video recordings, was 97%. Thresholds for disability were defined as moderate/severe <70; mild 70-84; none >85. Local ethical approval and parental consent were obtained.
Results: Median Bayley-3 Cognitive Composite (CC) score (100 [65-125]) was 9 points higher than median Bayley-2 Mental Developmental Index (MDI) score (91 [37-121]). Median Bayey-3 Motor Composite score (100 [58-124]) was 17 points higher than median Bayley-2 Psychomotor Developmental Index (PDI) score (83 [29-107]). Of the 10 children with Bayley-2 MDI <70, only 3 had Bayley-3 CC scores <70 and 7/10 had scores <85. Of the 11 children with Bayley-2 PDI <70, 3 had Bayley-3 MC scores <70 and 11/11 had scores <85. The relationship between different scores was explored using correlation analysis and score comparisons with the strongest correlations were used to derive regression equations from linear regression analysis. Estimated Bayley-2 Index scores derived from the equations were found to restore the number of infants classified with moderate/severe (<70) and mild (<85) degrees of developmental delay to similar proportions found using observed Bayley-2 scores.
Conclusion: Fewer children had scores <70 using Bayley-3 than with Bayley-2. This finding prohibits the direct comparison of Bayley-3 and Bayley-2 scores in infants with NE. Linear regression equations for cognitive and motor development can facilitate more direct comparison of Bayley-2 and Bayley-3 outcomes in cooled infants surviving NE.
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