Search

Background Numerous studies indicated that infants born small-for-gestational-age (SGA) are at higher risk of overweight. However, the association between SGA and overweight may be due to overcontrolling for body size. This study aimed to analyze the effect of controlling for child’s weight and height in the association between SGA and overweight in children born preterm. Methods Data were obtained from the Preterm Infant Multicenter Growth Study (n = 1089). The association between SGA and overweight at 36 months corrected age (CA) was analyzed using logistic regression models: 1) crude, 2) adjusted for baseline covariates, 3) adjusted for baselines covariates with additional adjustments separately for child’s weight and height at 21 months CA. Marginal structural models (MSM) with stabilized inverse probability weights were used to estimate the direct effect of SGA on overweight. Results The crude and adjusted models yielded a null association (OR, 95% CI: 0.88, 0.26-2.96; 0.95, 0.28-3.29). Adjusting for later height reversed the effect (OR, 95% CI: 2.31, 0.52-10.26), and adjusting for later weight reversed the effect and provided a significant association (OR, 95% CI: 6.60, 1.10-37.14). The MSMs with height and weight considered as mediators indicated no direct effect of SGA on overweight (OR, 95% CI: 0.83, 0.14-5.01; 0.71, 0.18-2.81). Conclusions Overcontrolling for body size can falsely induce an association between SGA and overweight. Key messages Mediators should not be treated as confounders.