Breastfeeding duration, maternal body mass index, and birth weight are associated with differences in body mass index growth trajectories in early childhood.

Accelerated postnatal growth is an important predictor for obesity risk. It is unknown whether early-life obesity-related risk factors affect body mass index (BMI) growth rates during distinct growth periods from early infancy through preschool years. We examined whether breastfeeding duration, maternal BMI, and birth weight are associated with growth trajectories of age- and sex-standardized WHO BMI z scores (zBMIs) in young children. Children (n = 5905) in The Applied Research Group for Kids (TARGet Kids!) prospective cohort study underwent repeated measures of weight and length or height from birth to 10 y of age. Piecewise linear mixed models were used to determine whether zBMI growth rates differ for each risk factor during periods of growth between birth and 1, 3, 18, 36, and 72 mo of age. Children who were breastfed < 6 mo compared with 6 mo showed a higher growth rate between 1-3 and 3-18 mo, resulting in higher standardized BMIs (zBMIs) of +0.24, +0.12, and +0.19 at 18, 36, and 72 mo, respectively. Maternal BMI (in kg/m(2)) 30 compared with < 30 resulted in higher growth rates between 1-3 and 36-72 mo and higher zBMIs of +0.22, +0.14, +0.18, and +0.41 at 3, 18, 36, and 72 mo, respectively. Infants weighing < 2.5 kg at birth (compared with 2.5-4 kg) experienced higher growth rates between 1-3 and 3-18 mo but had lower zBMIs at all time points (zBMI: -1.45 to -0.21). Infants weighing 4 kg at birth (compared with 2.5-4 kg) had significantly lower growth rates in the first 3 mo but higher zBMIs at all time points (zBMI: +1.16 to +0.27). Differences in zBMI growth rates by breastfeeding duration, maternal BMI, and birth weight are seen in early infancy and contribute to differences in zBMI, which persist into midchildhood. This trial was www.clinicaltrials.gov as NCT01869530.