Does Growth Velocity Affect Associations Between Birth Weight and Neurodevelopment for Infants Born Very Preterm?

OBJECTIVE: To determine how neonatal growth velocity affects the association between birth weight (BW) and neurodevelopmental outcomes in infants born preterm.

STUDY DESIGN: This study is a secondary analysis of the MOBYDIck randomized multicenter trial conducted in breastfed infants born at <29 weeks' gestational age (GA), whose mothers were supplemented with docosahexaenoic acid or placebo during the neonatal period. Neurodevelopmental outcomes were assessed at 18 to 22 months of corrected age using the Bayley-III Cognitive and Language composite scores. The role of neonatal growth velocity was assessed with causal mediation and linear regression models. Subgroup analyses were stratified by BW z-score categories (<25th ; ≥25th - ≤75th ; >75th percentile).

RESULTS: Neurodevelopmental outcomes were available for 379 children (mean GA=26.7 weeks, SD 1.5). Growth velocity partially mediated the relationships between BW and Cognitive (ß=-1.1 [95% CI, -2.2 to -0.02], P=0.05) and Language scores (ß=-2.1 [95% CI, -3.3 to -0.8], P=0.002). An increase by 1 g/kg/day in growth velocity was associated with an increase by 1.1-point in the Cognitive score (95% CI, -0.03 to 2.1, P=0.06) and 1.9-point in the Language score (95% CI, 0.7 to 3.1, P=0.001), after adjustment for BW z-score. For children with BW <25th percentile, a 1 g/kg/day increase in growth velocity was associated with an increase by 3.3-points in Cognitive score (95% CI, 0.5 to 6.0, P=0.02) and 4.1-points in Language score (95% CI 1.3 to 7.0, P=0.004).

CONCLUSION: Postnatal growth velocity mediated the relationship between BW and neurodevelopmental performance, with larger effects for children with lower BW.