Routine Life-Course Health Records in Infancy Predict Being Overweight in Childhood and Adolescence: The TMM BirThree Cohort Study

<b>Background/Objectives</b>: Being overweight in childhood is a strong predictor of later obesity and related health disorders, underscoring the importance of the early identification of at-risk children. The aim of this study was to develop a prediction model for being overweight across childhood and adolescence using routine life-course health records available up to 18-23 months of age. <b>Methods</b>: We analyzed 1581 participants from the Tohoku Medical Megabank Birth and Three-Generation Cohort Study and constructed multivariable logistic regression models to predict being overweight at 36-47 months, 6 years, 11 years, and 14 years. Predictors included being overweight at 18-23 months, maternal characteristics, birth weight, and body mass index changes from birth to 18-23 months. Model performance was evaluated using the area under the curve (AUC), calibration, Brier scores, risk by score range, and stratified 10-fold cross-validation to assess the stability and robustness of predictive performance. <b>Results</b>: Being overweight at 18-23 months consistently showed strong associations with later overweight status. Model discrimination was moderate to high for early and middle childhood (AUC 0.873 at 36-47 months; 0.772 at 6 years) but modest for adolescence (AUC 0.720 and 0.692 at 11 and 14 years). Cross-validation demonstrated stable predictive performance across all age groups. Calibration and overall predictive accuracies were acceptable across all age groups. <b>Conclusions</b>: These results indicate that routine early life-course health records moderately predict the risk of being overweight, supporting their practical potential for early preventive interventions.