Hypercoagulability and altered lipid metabolism, which are observed in normal pregnancy, can be enhanced in diabetes mellitus. The aim of the study was to evaluate the influence of glycemic control on coagulation and lipid metabolism in women with pregestational (PGDM) and gestational (GDM) diabetes treated with insulin. There were 50 patients with PGDM and 101 patients with GDM enrolled into the study. Serum lipid and coagulation parameters were assessed at 18-22, 25-28, and 31-34 weeks of pregnancy and were compared within the diabetic groups with reference to the effectiveness of glycemia control. We found that poor glycemic control was associated with shortened activated partial thromboplastin time (APTT) and increased activity of antithrombin III (ATIII) in both diabetic groups and with a higher plasminogen activator inhibitor (PAI-1) content level in the GDM group. Poorly controlled PGDM was associated with higher levels of total cholesterol and high-density cholesterol (HDL) in the second trimester and triglycerides in the third trimester. In patients with poorly controlled GDM, a higher concentration of HDL was observed in third trimester, whereas a higher triglyceride level was found in both second and third trimesters. Positive correlations between total cholesterol and APTT and between triglyceride and APTT and ATIII were found in the poorly controlled PGDM group. We conclude that poor glycemic control of diabetic pregnancy impacts both lipid metabolism and the blood coagulation system.