Purpose: The aim of this study was to evaluate glucagon-like peptide-1 (GLP-1) levels, lipid parameters, thyroid-stimulating hormone (TSH), c peptide and glycated hemoglobin (A1C) values in pregnant women at high-risk for gestational diabetes mellitus (GDM). Material and Method: In this cross-sectional study, we included pregnant women at high-risk for GDM who attended the endocrinology and metabolic diseases outpatient clinics at İzmir Katip Çelebi University Atatürk Training and Research Hospital between January 2013 and April 2013. Twenty pregnant women with GDM and eleven without GDM participated in the study. The dependent variable in the study was GDM that was evaluated by 75 mg oral glucose tolerance test (OGTT). Independent variables were the levels of glucose, A1C, insulin, c-peptide, GLP-1, TSH, and lipid parameters, all evaluated in fasting blood samples. Besides, glucose, insulin, c-peptide, GLP-1 levels during OGTT were also evaluated in blood samples collected at 60 and 120 minutes. Results: While fasting insulin levels were statistically significantly higher among women with GDM, there was no statistically significant difference in the levels at 60 and 120 minutes between the two groups. There was no significant difference in fasting c-peptide levels and c-peptide levels at 60 minutes during OGTT between the two groups, however, c-peptide levels at 120 minutes were higher in women with GDM. The women with GDM was found to have lower fasting GLP-1 levels than women without GDM. Although it was not significant, GLP-1 levels at 60 and 120 minutes were also lower among women with GDM. Discussion: A decrease in GLP-1 levels may have a role in the etiopathogenesis of GDM and type 2 diabetes mellitus.