At baseline, all women will have a standardized medical history, physical, and laboratory examination. Plasma glucose, insulin, pro-insulin, C-peptide, glucagon, adipokines, pro-inflammatory molecules, and lipid profile will be determined in fasting condition. A 75g OGTT will be performed after an overnight fasting and sample will be drawn at 15, 30, 60, 90 and 120 minutes for plasma glucose, C-peptide, glucagon and GLP-1 determinations. Women with IFG or IGT will be recruited and undergo to a hyperglycemic clamp with arginin bolus at the end of the test. Then the women will be randomized in 3 treatment groups: metformin (850 mg bid), sitagliptin (100 mg qd)or metformin (850 mg bid) + sitagliptin (100 mg qd). After 4-month treatment, the baseline evaluation will be repeated.