Before Se supplementation, pregnant women with GDM had significantly lower plasma Se level associated with fasting hyperglycemia, and were more vulnerable to oxidative stress increase, whose levels of plasma and erythrocyte MDA and PC were significantly higher, and levels of all studied markers of antioxidant defence (erythrocyte enzymatic activities of GPx, GRase, CAT and SOD) were reduced compared to healthy women group with normoglycemic pregnancies (Table 2). This evidence concerns the gene CAT and gestational diabetes.