OBJECTIVE
To examine associations of birth size and weight gain during 4 early-life age intervals with midchildhood adiposity and metabolic profile and to evaluate for an interaction between birth size and early-life weight gain.
STUDY DESIGN
Using data from 963 participants of Project Viva, a US prebirth cohort, we used multivariable linear regression to examine relations of birth size (tertiles of birthweight-for-gestational-age z-score) and weight gain (body mass index z-score [BMIZ] change) during 4 age intervals (birth-6 months, 6 months-1 year, 1-2 years, 2-3 years) with body composition and metabolic biomarkers during midchildhood (6.6-10.7 years).
RESULTS
After accounting for confounders and previous growth, greater BMIZ change during all 4 age intervals corresponded with higher midchildhood adiposity, with larger effect sizes for later (1-2 years and 2-3 years) vs earlier (birth-6 months and 6 months-1 year) time frames. We observed effect modification by birth size for the birth-6 months and 6 months-1 year intervals. Greater birth-6 months BMIZ change was associated with higher overall adiposity (0.40 [95% CI 0.29, 0.51] kg dual x-ray absorptiometry total fat mass per z-score) among children in the highest birth size tertile. Similar associations were observed for central adiposity. Each increment in 6 months-1 year BMIZ change corresponded with 0.55 (0.05, 1.05) units higher homeostatic model assessment of insulin resistance and 2.68 (0.96, 4.40) ng/mL higher leptin among the smallest infants.
CONCLUSIONS
BMIZ gain after 1 year is associated with greater midchildhood adiposity regardless of birth size, whereas the long-term influence of weight gain during the first postnatal year may depend on size at birth. Future studies are warranted to validate findings and examine relations with conventional birth size cut-offs.