© 2021, Universidad de la Frontera. All rights reserved.GDM is linked with overexpression of inflammatory cytokines and increased oxidative stress, leading to endothelial dysfunction and vascular disorder. Weaimed to examine the expression of ADAMTS13 and PCNA in the placentas of gestational diabetes mellitus (GDM) patients to investigate the effects of hypoxia, induced by GDM, on proliferation and extracellular matrix formation in the maternal and fetal placenta cells. A total of 60 placentas were collected from pregnant women admitted to the obstetrics clinic. Thirty of them were diagnosed with GDM, and 30 of them were diagnosed with non-GDM patients. Samples were fixed in 10 % formaldehyde, after routine follow-up, embedded in paraffin wax. Sections of 5 µm were cut stained with Mayer Hematoxylin-Eosin, examined under a light microscope. Sections for immunohistochemical analysis were cut and processed for antigen retrievalin citrate solution. Sections were incubated with ADAMTS13 and PCNA primary antibodies, counterstained with hematoxylin, and evaluate under a light microscope. In histopathological examination, the non-diabetic placentas showed that decidua cells in the maternal region were polygonal with oval nuclei and organized in groups. In the GDM group, there were pyknosis and apoptotic changes in decidua cell nuclei. Vacuolar areas were observed in large cavities in maternal connective tissue. Inflammation and dilatation with congestion were observed in the blood vessels of the villus. In the GDM group, positive ADAMTS13 expression was observed in the decidua cells vascular endothelial cells, and surrounding connective tissue fibroblast cells. In the GDM group, a significant increase in PCNA expression was observed in decidua cells, connective tissue cells and endothelial cells. Functional changes in ADAMTS13 proteases and PCNA were thought to induce maternal and fetal complications by stimulating extracellular matrix development.