BACKGROUND: Limited research has examined the potential association between triglyceride glucose-body mass index (TyG-BMI) and gestational diabetes mellitus (GDM). The objective of this investigation was to analyze this linkage and evaluate TyG-BMI's capability to predict GDM. METHODS: This research employed secondary data derived from a prospective cohort in South Korea, which included 588 pregnant women with singleton gestations, collected between November 2014 and July 2016. To investigate the connection between TyG-BMI and GDM, logistic regression and sensitivity analyses were performed. Furthermore, an analysis of receiver operating characteristics (ROC) was conducted to assess the prognostic accuracy of TyG-BMI in relation to GDM. RESULTS: The cohort exhibited a mean age of 32.07 ± 3.80 years, with 36 individuals (6.12%) manifesting GDM during the interval of 24 to 28 weeks of gestation. Following the adjustment for possible confounding variables, an increased TyG-BMI was associated with an elevated risk of GDM, as indicated by an odds ratio (OR) of 1.02 (95% CI: 1.01-1.04). Additionally, the area under the curve (AUC) for TyG-BMI's predictive performance was recorded at 0.7979 (0.7143-0.8814), with an optimal threshold established at 211.03, which resulted in a specificity of 86.23% and a sensitivity of 66.67%. CONCLUSIONS: In this South Korean cohort, increased TyG-BMI during early pregnancy (10-14 weeks) was significantly associated with the onset of GDM (during pregnancy 24-28 weeks). TyG-BMI could be integrated into clinical practice as a complementary preliminary screening tool for detecting women who are at increased risk of GDM.