Are small-for-gestational-age preterm infants at increased risk of overweight? Statistical pitfalls in overadjusting for body size measures.

OBJECTIVE

The objective of this study is to analyze the effect of adjusting for body measures on the association between small for gestational age (SGA) and overweight at 3 years.

STUDY

DESIGN

Data were obtained from the Preterm Infant Multicenter Growth Study (n = 1089). Logistic regression was used, to adjust for confounders with additional adjustments separately for weight and height at 21 months. Marginal structural models (MSMs) estimated the direct effect of SGA on overweight.

RESULTS

The crude and adjusted for confounders models yielded null associations between SGA and overweight. Adjusting for height yielded a positive association (odds ratio (OR): 2.31, 95% CI: 0.52-10.26) and adjusting for weight provided a significantly positive association (OR: 6.60, 95% CI: 1.10-37.14). The MSMs, with height and weight held constant, provided no evidence for a direct effect of SGA on overweight (OR: 0.83, 95% CI: 0.14-5.01, OR: 0.71, 95% CI: 0.18-2.81, respectively).

CONCLUSION

Adjusting for body measures can change the association between SGA and overweight, providing spurious estimates.