OBJECTIVE : The primary aim of this study was to investigate the effect of gestational diabetes mellitus (GDM) on the quality of life (QoL) of pregnant women during the third trimester of pregnancy. The secondary aim was to compare the QoL of pregnant women with GDM according to their therapeutic approach. This is the first study of this kind conducted in Greece. METHODS : A case-control study with 62 pregnant women (31 with GDM and 31 with uncomplicated pregnancy), during the third trimester of pregnancy. QoL and Health Related QoL were studied with the use of three questionnaires (EQ-5D-5L, WHOQOL-BREF and ADDQoL). RESULTS : A decrease in the QoL was found in pregnant women with GDM compared with pregnant women with uncomplicated pregnancy (p < 0.05) regarding both social life and health scales. On the contrary, there was no difference in the QoL between pregnant women with GDM who followed different treatment approaches (diet or insulin). CONCLUSIONS : The diagnosis of GDM is associated with a reduction in the QoL of pregnant women during the third trimester of pregnancy, while the type of treatment does not seem to further affect it. More studies should be conducted so that the modifiers of this association can be clarified.