BackgroundAppropriate weight gain reduces the risk of fetal macrosomia and large for gestational age (LGA) in women with gestational diabetes mellitus (GDM), especially in the second and third trimester. This study aims to identify the optimal weight g–ain for such women across several pre-pregnancy body mass index (BMI) categories to lower the risk of macrosomia and LGA. MethodsThis retrospective cohort study enrolled women with GDM in north Taiwan who delivered between January 2012 and July 2022. BMI cut-offs were based on Chinese-specific guidelines and used to classify the participants as underweight (<18.5 kg/m2), normal weight (18.5–24.0 kg/m2), overweight (24.0–28.0 kg/m2), or obese (>28 kg/m2). Receiver operator curve analysis was used to determine the optimum GWG cut-off ranges to predict macrosomia / LGA, and uni- and multivariate analyses were used to analyze risk factors. In addition, a multivariable model predicting macrosomia and LGA in infants was developed. ResultsA total of 963 participants was included in our analysis. Optimal mean weekly rates of GWG in the second and third trimesters were 0.43 kg/week and 0.61 kg/week, respectively, in the underweight and normal weight group, and 0.33 kg/week and 0.32 kg/week, respectively, in the overweight and obesity group. ConclusionThe 2009 IOM guidelines, offering weight gain recommendations for pregnant women, appear to be applicable to Asian women diagnosed with GDM. This indicates that it is essential for such women to maintain an adequate total GWG throughout pregnancy. Physicians should address GWG using the IOM guidelines and trigger intervention when it is required to reduce macrosomia and LGA occurrence.