AIMS: To evaluate the ability of first trimester plasma glycated CD59 (pGCD59) to predict gestational diabetes mellitus (GDM) at 24-28 weeks of gestation. METHODS: Prospectively, in 378 pregnant women, GDM was diagnosed using the one step 2 h 75 g oral glucose tolerance test adjudicated by the World Health Organisation (WHO) 2013 criteria. The ability of pGCD59 to predict GDM was assessed using receiver operating characteristic (ROC) curves adjusted for maternal age, body mass index (BMI), maternal ethnicity, parity, previous GDM, family history of diabetes mellitus and week of gestation at time of pGCD59 sampling. RESULTS: pGCD59 generated an adjusted area under the curve (AUC) of (a) 0.63 (95 %CI:0.56-0.70, p < 0.001) for predicting GDM, and (b) 0.71 (95 %CI:0.62-0.79, p < 0.001 for GDM diagnosed with a fasting plasma glucose (FPG) ≥ 5.1 mmol/L. Sensitivity analysis of BMI subgroups showed that pGCD59 generated the highest AUC in the 35 kg/m2 ≤ BMI < 40 kg/m2 (AUC:0.85, 95 %CI:0.70-0.98) and BMI ≥ 40 kg/m2 (AUC:0.88, 95 %CI:0.63-0.99) categories. CONCLUSIONS: Early in pregnancy, pGCD59 may be a good predictor of GDM in women with a high BMI and a fair predictor of GDM diagnosed by an elevated FPG independent of BMI.