Differences in BMI trajectory for infants in different birth weight classes

Deviations from normal postnatal growth patterns in infancy and early childhood are indicators to predict future negative health outcomes and to direct early interventions, such as changes in feeding regimens. The objective of our study was to examine potential differences in BMI trajectory during the first year of life between infants of different birth weight categories. A pooled, fully anonymized dataset was constructed based on individual subject data of 4,777 participants from 12 clinical studies in which infant growth outcome measurements were collected at several timepoints during their first year of life. A BMI model was constructed using a joint bivariate growth model for weight and height (and their deterministic relationship). A Bayesian approach was used to explore birthweight category-specific differences in BMI development. Our main finding is that the BMI trajectories of the birthweight categories (particularly the small vs large groups) continue to show differences over time, although these differences become less apparent after the first months of age. Both weight and length continue to show consistent differences between categories across the first year of life. A more detailed analysis including the effect of region and gender, showed differential BMI patterns among the three birthweight categories over time across the different subgroups (combinations of region and gender).