Gestational weight gain trajectories and outcome-informed reference ranges among women with gestational diabetes: a BMI-stratified cohort study

Background Gestational weight gain (GWG) is an important modifiable component of nutritional management in gestational diabetes mellitus (GDM), but stage-specific patterns and appropriate total GWG ranges across pre-pregnancy body mass index (BMI) categories remain uncertain. This study aimed to characterize gestational-age-specific GWG trajectories and stage-specific patterns in relation to GDM diagnosis based on oral glucose tolerance testing (OGTT), derive BMI-stratified local reference ranges for total GWG, and internally compare their risk-stratification performance with national recommendations. Materials and methods This retrospective cohort study included 9,008 women with singleton pregnancies complicated by GDM who delivered between February 2021 and December 2025. Population-level centile curves characterized GWG patterns, and the interquartile range of total GWG among women without adverse pregnancy outcomes (APOs) defined the locally derived, outcome-informed empirical reference range (LOC). Generalized additive models and multivariable logistic regression assessed associations between GWG and APOs. LOC and National Health Commission (NHC) discrimination was internally evaluated using 2,000 bootstrap resamples with optimism correction. Results GWG showed stage- and BMI-specific patterns, increasing more rapidly before OGTT-based diagnosis and generally slowing thereafter. Post-diagnosis rates approached NHC recommendations among underweight or normal-weight women but remained relatively high among overweight or obese women. The LOC ranges were 11.0–15.0, 9.2–14.0, 7.5–13.0, and 6.0–11.5 kg for underweight, normal weight, overweight, and obesity, respectively. After false discovery rate correction, inadequate GWG was associated mainly with low birth weight (LBW) and small for gestational age (SGA), whereas LOC-based associations with preterm birth in underweight and normal-weight women were less robust in the 28-week landmark analysis. Excessive GWG was primarily associated with preeclampsia, macrosomia, large for gestational age (LGA), and cesarean section, particularly among women with normal weight or overweight. After bootstrap correction, LOC and NHC showed broadly comparable discrimination, with exploratory numerical advantages for LOC in selected BMI–outcome combinations. Conclusion GWG trajectories and locally derived total GWG ranges differed across pre-pregnancy BMI categories. The locally derived ranges were broadly consistent with national recommendations and may provide supplementary information for selected BMI–outcome combinations. These findings may inform prospective evaluation of stratified, dynamic weight-management approaches within the framework of national recommendations.