Objective: In this study we aimed to compare blood count parameters such as; mean platelet volume (MPV), platelet count (PC), and platelet distribution width (PDW), white blood count (WBC), hemoglobin (HMG), hematocrit (HCT), lymphocyte (LYM ), neutrophil (NEU), PC/MPV, PC/LYM, PC/WBC, NEU/LYM rates; between healthy pregnant women and pregnant women with Gestational Diabetes Mellitus (GDM) whether these parameters have a predictive value of GDM. Methods: A retrospective case control study was performed and a total of 202 pregnant women including 78 pregnant women with GDM (38.6%) and 124 healthy pregnant women (61.4%; the control group) were fallen under the study. Prior medical histories had no particularity. Results: The result of compared parameters between GDM and Control Groups; there was no significant difference between any variables except age (p=0.024; p<0.05). Conclusion: If blood samples are evaluated under healthy conditions ( rapidly collection, transfer and studying) we concluded that blood count parameters would not be useful for predicting the diagnosis of GDM.