Gestational diabetes mellitus (GDM) is increasing partly due to the obesity epidemic. Adipocytokines have thus been suggested as first trimester screening markers for GDM. In this study we explore the associations between body mass index (BMI) and serum concentrations of adiponectin, leptin, and the adiponectin/leptin ratio. Furthermore, we investigate whether these markers can improve the ability to screen for GDM in the first trimester.