Counterbalanced Comparison of the BSID-II and Bayley-III at Eighteen to Twenty-two Months Corrected Age.

OBJECTIVE: To evaluate differences in developmental assessments using the current version of the Bayley Scales of Infant Development (Bayley-III) as compared to the older BSID-II. Previous studies suggest that average scores on the Bayley-III may be significantly higher than scores on the previous version, but the magnitude and potential impact of differences between these 2 assessments are uncertain.

METHODS: We enrolled 77 former preterm infants (born <32 wk gestation and ≤2000 g) at 18 to 22 months corrected age in this randomized crossover study. The Bayley-III was administered in follow-up clinic per standard of care. The BSID-II was administered during a separate study visit. The order of testing was randomly assigned. The assessments were performed 4 to 8 weeks apart by masked personnel. The main outcomes were mean difference between BSID-II Mental Development Index (MDI) and Bayley-III Cognitive Composite score, mean difference between BSID-II Psychomotor Development Index (PDI) and Bayley-III Motor Composite score, and difference in the proportion of infants classified as having "developmental delay."

RESULTS: Bayley-III scores were significantly higher across the range of scores and in all domains. Mean Cognitive Composite scores were almost 1 SD higher than MDI scores (14.1 ± 12.9 points, p < .001). Mean Motor Composite scores were 9.0 ± 11.9 points higher than PDI scores (p < .001). When severity of delay was classified using standardized cut-points for moderate and severe developmental delay (1 and 2 SDs below reference norm), 40% of children (n = 31/77) were classified as less severely delayed with the Bayley-III Cognitive Composite score than with the BSID-II MDI, whereas only 1 (<2%) was classified as more severely delayed with the Bayley-III (p < .001).

CONCLUSION: These findings have critical implications for both the interpretation of clinical research studies and determination of eligibility for services in high-risk children.