<p>The metabolic score for insulin resistance (METS-IR) is a non-insulin-based surrogate marker of insulin resistance. However, its utility for identifying gestational diabetes mellitus (GDM) risk in early pregnancy remains unclear. This study included 585 singleton pregnant women from a prospective cohort study in South Korea. METS-IR was assessed at 10–14 weeks of gestation. Multivariable logistic regression was used to examine the association between METS-IR and subsequent GDM. Subgroup and sensitivity analyses were performed to evaluate the robustness of the findings, and receiver operating characteristic curve analysis was used to assess the predictive performance of METS-IR. Among 585 participants, 36 women developed GDM. In the fully adjusted model, METS-IR remained positively associated with GDM when analyzed as a continuous variable (OR = 1.18, 95% CI: 1.10–1.26, P &lt; 0.001). Compared with women in the lowest METS-IR tertile, those in the highest tertile had a higher risk of GDM (OR = 5.50, 95% CI: 1.43–21.06, P = 0.013). The association was consistent in subgroup and sensitivity analyses. METS-IR showed good discriminative ability for GDM, with an area under the curve of 0.808 (95% CI: 0.726–0.890). The optimal cutoff value was 34.5, with a sensitivity of 66.7% and specificity of 86.9%. Higher METS-IR at 10–14 weeks of gestation was independently associated with an increased risk of GDM. METS-IR may serve as a simple early-pregnancy marker to help identify women at high risk for GDM.</p>