Low length/weight growth trajectories of early-term infants during the first year: evidence from a longitudinal study in China

OBJECTIVE: To identify common length, weight and body mass index (BMI) growth trajectories of term infants during infancy, and to determine their association with early-term infants. DESIGN: Prospective longitudinal study. SETTING: Wuhan, China. PATIENTS: A total of 4308 term infants (born at 37–41 weeks of gestation) were included. All term infants were single live birth with no defects and birth weight ≥2500 g, and their mothers were permanent residents of Wuhan for more than 2 years. After excluding 887 infants, a total of 3421 term infants (1028 early-term infants born at 37–38 weeks of gestation and 2393 full-term infants born at 39–41 weeks of gestation) entered the statistical analysis stage. MAIN OUTCOME MEASURES: Patterns of length, weight and BMI growth trajectories by using group-based trajectory modelling. RESULTS: Three distinct physical growth trajectories were identified as follows: length: low stable (1056, 30.9%), moderate stable (1887, 55.2%) and high increasing (477, 13.9%); weight: low stable (1031, 30.1%), moderate stable (1884, 55.1%) and high increasing (505, 14.8%); BMI: low stable (689, 20.1%), moderate stable (2167, 63.4%) and high increasing (564, 16.5%). Compared with the full-term infants, early-term infants were more likely to remain at low-stable trajectory in length (OR: 1.40; 95% CI: 1.19 to 1.66) and weight (OR:1.29; 95% CI: 1.09 to 1.53). These associations were still statistically significant after adjusting potential confounders and were more evident among girls in the stratified analysis. There was no statistical association between BMI trajectory patterns and gestational age categories. CONCLUSION: Our results suggested the heterogeneity of term infants existed in length, weight and BMI growth trajectories of early childhood. Compared with full-term birth, early-term birth was related to low length and weight trajectories rather than BMI trajectory. Further research is needed to evaluate the duration of these low trajectories and their possible long-term health effects.