Background This study aimed to design a simple surrogate marker (i.e., predictor) of the minimal model glucose effectiveness (S G ), namely calculated S G (CS G ), from a short insulin-modified intravenous glucose tolerance test (IM-IVGTT), and then to apply it to study women with previous gestational diabetes mellitus (pGDM). Methods CS G was designed using the stepwise model selection approach on a population of subjects ( n =181) ranging from normal tolerance to type 2 diabetes mellitus (T2DM). CS G was then tested on a population of women with pGDM ( n =57). Each subject underwent a 3-hour IM-IVGTT; women with pGDM were observed early postpartum and after a follow-up period of up to 7 years and classified as progressors (PROG) or non-progressors (NONPROG) to T2DM. The minimal model analysis provided a reference S G . Results CS G was described as CS G =1.06×10 −2 +5.71×10 −2 ×K G /G peak , K G being the mean slope (absolute value) of loge glucose in 10–25- and 25–50-minute intervals, and G peak being the maximum of the glucose curve. Good agreement between CS G and S G in the general population and in the pGDM group, both at baseline and follow-up (even in PROG and NONPROG subgroups), was shown by the Bland-Altman plots (<5% observations outside limits of agreement), and by the test for equivalence (equivalence margin not higher than one standard deviation). At baseline, the PROG subgroup showed significantly lower S G and CS G values compared to the NONPROG subgroup ( P <0.03). Conclusion CS G is a valid S G predictor. In the pGDM group, glucose effectiveness appeared to be impaired in women progressing to T2DM.