Development of Thai-Specific Gestational Weight Gain Targets Using Asian BMI Cut-Points: Implications for Nursing and Midwifery Practice in Preventing Gestational Diabetes Mellitus

Background: Thai obstetric nurses follow WHO gestational weight gain (GWG) guidelines to prevent gestational diabetes mellitus (GDM). However, these Western-derived guidelines misclassify approximately 16% of Thai pregnant women, who carry excess metabolic risk at lower BMI values than Western populations. Objectives: To derive and validate Thai-specific GWG targets using Thai BMI cut-points across five BMI subgroups and assess implications for nursing practice in GDM prevention. Methods: Retrospective cohort study of 1396 Thai singleton pregnancies at a maternal and child hospital (2023–2025). GWG targets were derived as interquartile ranges (P25–P75) from a healthy-outcomes subgroup (n = 706), with validity confirmed by multivariable logistic regression and a 70:30 derivation/validation split. Results: GDM prevalence was 15.8%, with a rising crude trend that was attenuated after accounting for a mid-study change in screening protocol. Provisional Thai-specific GWG targets were underweight/normal weight 11.5–18.0 kg, overweight 9.7–18.0 kg, obesity class I 9.1–16.0 kg, and obesity class II+ 5.8–12.1 kg. Inadequate GWG in obesity class I was associated with a 3.92-fold GDM risk increase (aOR 3.92, 95% CI 2.12–7.24, p < 0.001). Adherence improved from 34.7% (IOM 2009) to 50.2% with Thai-specific targets. Conclusions: These Thai-specific GWG targets are provisional, single-centre pilot estimates. They appear clinically safe and are substantially more achievable than IOM 2009 criteria and are offered to inform BMI-appropriate antenatal counselling and to justify a multi-centre validation study, rather than as ranges that are ready for immediate national adoption.