Association of Early-Term and Full-Term Delivery With Overweight and Obesity Risk in the First Year of Life

Importance: The association between gestational age (GA) and overweight/obesity risk has been studied in preterm infants, but remains underexplored in term infants, who account for the majority of live births. Objective: To determine whether early-term (GA 37-38 weeks) or full-term (GA 39-40 weeks) delivery is associated with early childhood overweight and obesity risk. Design, SETTING, AND PARTICIPANTS: This cohort study included healthy term infants (GA 37-40 weeks) born between January 2011 and July 2022 at two tertiary hospitals in Shandong, China. Infants with congenital malformations or syndromes were excluded. In accordance with local health assessment protocols, length and weight were measured by trained professionals at four time points: 1-3, 4-6, 7-9, and 10-12 months. Data analysis was conducted in September 2024. Exposures: GA was obtained from clinical records. Early-term delivery compared against full-term delivery as the reference group. Main Outcomes and Measures: Body Mass Index (BMI) was calculated, and BMI-for-age Z-scores (BAZ) were derived using the World Health Organization growth standards. Risk of overweight and obesity was defined as BAZ>1. Results: Among 5,092 participants with complete data, 26.6% (n=1,355) were early-term. The prevalence of overweight and obesity risk was significantly higher in early-term infants (27.6%-30.2%) compared to full-term infants (23.6%-26.4%) throughout infancy. Early-term delivery was associated with an increased risk of overweight and obesity from 1-3 months (unadjusted odds ratio [OR], 1.162; 95% confidence interval [CI], 1.001-1.340; P =.038) to 10-12 months of age (unadjusted OR, 1.236; 95% CI, 1.073-1.426; P =.004). This association remained significant after adjusting for mode of delivery, parity, number of fetuses, sex, feeding practices during the first six months, and birth weight. Multiple imputation analysis for missing covariates yielded similar results. Conclusions and Relevance: Early-term infants have a higher risk of overweight and obesity during the first postnatal year. These findings highlight the need for targeted interventions to prevent childhood obesity in this population.