Aim: Gestational diabetes mellitus (GDM) is associated with an increased risk of fetal and maternal complications, such astype 2 DM (diabetes mellitus) and cardiovascular disease (CVD). This study aimed to predict the potential for future vascular complications in mothers with GDM by evaluating oxidative stress, endothelial NO synthase (eNOS) expression, and vascular smooth muscle cell (VSMC) proliferation in the umbilical vessels of mothers with GDM. Material and Methods: Subjects were divided into two groups: the normoglycemic control (NGC) group (n = 10) and the GDM group (n = 12). Expression of eNOS and production of reactive oxygen species (ROS) in human umbilical vein endothelial cells (HUVECs) were determined. The mitochondrial mass of HUVECs was evaluated by spectrofluorometry. VSMC proliferation was ascertained in vitro with an EdU cell proliferation assay. Advanced glycation end products (AGEs) accumulation was measured by ELISA and assessed by immunohistochemical staining Results: VSMC proliferation, eNOS expression, and ROS production in HUVECs were significantly increased, and greater immunohistochemical staining to AGEs was observed in endothelium in GDM. Conclusion: Increased oxidative stress, which elevates eNOS expression and VSMC proliferation in the umbilical vessels of mothers with GDM, may be a sign that mothers have a high potential for developing diabetes or cardiovascular disease in the future.