Birth weight, infant growth, and childhood body mass index: Hong Kong's children of 1997 birth cohort

Objective: To investigate the association between birth weight, infant growth rate, and childhood adiposity as a proxy for adult metabolic or cardiovascular risk in a Chinese population with a history of recent and rapid economic development. Design: Prospective study in a population-representative birth cohort. Setting: Hong Kong Chinese population. Participants: Six thousand seventy-five term births (77.5% successful follow-up). Main Exposures: Birth weight and growth rate (change in the weight z score) at ages 0 to 3 and 3 to 12 months. Main Outcome Measure: Body mass index (BMI) (calculated as the weight in kilograms divided by the height in meters squared) z score at about age 7 years. Results: Each unit increase in the weight z score at ages 0 to 3 and 3 to 12 months increased the BMI z score by 0.52 and 0.33, respectively. Children in the highest birth weight and growth rate tertiles had the highest BMI z scores. In the lowest birth weight tertile, increases in the weight z score at ages 0 to 3 months had a larger effect on the BMI z score in boys (mean difference, 0.88; 95% confidence interval 0.69-1.07) than in girls (mean difference, 0.52; 95% confidence interval, 0.33-0.71); these differences by birth weight, growth rate at ages 0 to 3 months, and sex were significant (P=.007). Conclusions: Faster prenatal and postnatal growth were associated with higher childhood BMI in a population with a recent history of rapid economic growth and relatively low birth weight, suggesting that maximal growth may not be optimal for metabolic risk. However, there may be a developmental trade-off between metabolic risk and other outcomes.