The associations of large-for-gestational-age and infant feeding practices with children's body mass index z-score trajectories: the Early Childhood Longitudinal Study, Birth Cohort.

Very few studies have examined if high birth weight and infant feeding practices have implications for the trajectory of body mass index (BMI) growth across the early childhood period. The goal of this study was to assess if large-for-gestational-age (LGA) and infant feeding practices (exclusive breastfeeding for 6 months, and early introduction of complementary food prior to 4 months) are associated with BMI z-score trajectories over the early childhood period. Group-based trajectory modelling (GBTM) methods were employed to describe and classify developmental BMI z-score trajectories (the outcome of interest) in children from 9 months to 4 years of age (n = 4497) born to prenatal non-smoking mothers in the Early Childhood Longitudinal Study, Birth Cohort (2001-2005). Further analyses examined if the identified BMI z-score trajectories varied systematically with the exposures, LGA and specific infant feeding practices, after accounting for sociodemographic and other early-life factors. Two BMI z-score trajectory groups were identified: normal BMI z-score (56.2%) and high BMI z-score (43.8%). Children who were LGA infants had 2.3 times (risk ratio 95% confidence interval: 1.2, 4.5) greater risk of being in high BMI z-score group relative to normal BMI z-score group. BMI z-score trajectory groups did not differ by infant feeding practices, after controlling for LGA at birth. Membership in the high BMI z-score group was associated with LGA, but not with infant feeding practices. Healthcare professionals should provide early obesity counselling to parents of LGA infants so that parents can take appropriate obesity prevention measures for their children.