Relationship between Test Scores Using the Second and Third Editions of the Bayley Scales in Extremely Preterm Children

ObjectiveTo define the relationship between current Bayley Scales of Infant and Toddler Development, Third edition (Bayley-III) scores and the Bayley Scales of Infant Development, second edition Mental Development Index (MDI) to aid the comparison of population outcomes.Study designMDI and Bayley-III cognitive/language scales were administered concurrently in 185 extremely preterm children (≤26 weeks) at 29-41 months of age. Cognitive and language scores were combined (combined Bayley-III score [CB-III scores]) for comparison with MDI scores.ResultsBayley-III cognitive and language scores were 10 and 3 points higher than MDI scores, respectively; CB-III scores were 7 points higher. The relationship between CB-III and MDI scores was not a simple offset: CB-III values were increasingly higher than MDI at lower scores. Bayley-III scores underidentified MDI scores <70 (sensitivity 58%; specificity 100%). An algorithm for converting Bayley-III scores into MDI scores improved predictive value (sensitivity 95%; specificity 97%). Bayley-III scores <80 were similarly predictive (sensitivity 89%; specificity 99%).ConclusionsWe recommend caution in the interpretation of Bayley-III scores in population studies as the correlation with the previous edition appears worse at lower test score values and the predictive value for IQ is as yet unclear.