Background Cross-sectional analyses at 6, 12, 24 months and 5.5 years, revealed positive intervention effects on child development in VLBW infants who were supported by the Infant Behavioural Assessment and Intervention Program© (IBAIP) as comparing to standard follow-up care. Longitudinal effects were not analysed yet.

AIM To investigate the longitudinal effects of the IBAIP in VLBW infants on cognitive and motor development.

Methods In a RCT, 86 VLBW infants received the IBAIP until 6 months CA, 90 VLBW infants received standard care. At 6, 12, and 24 months CA, cognitive and motor development were assessed with the Bayley Scales of Infant Development. At 5.5 years CA the Wechsler Preschool and Primary Scale of Intelligence and the Movement Assessment Battery for Children were used. Longitudinal data were analysed with linear mixed models in total group and three subgroups, using Z-scores generated from raw cognitive and motor scores.

Results A significant intervention effect (0.4SD) on motor development was found (p = 0.006). On cognitive development, a non-significant intervention effect over time was found (p = 0.063). In children with bronchopulmonary dysplasia (BPD) significant intervention effects were found for both cognitive (effect=0.7SD; p = 0.019) and motor (effect=0.9SD; p = 0.026) outcome. Maternal education hardly influenced intervention effects over time, but in children with combined biological and social risks a longitudinal intervention effect of 0.8SD was found on cognitive development (p = 0.044).

Conclusion The IBAIP leads to improved motor development in VLBW infants, and in infants with BPD also to improved cognitive development, over a five years period after the intervention.