Objective: To explore the trend of gestational diabetes (GDM) prevalence, as well as fasting, 1-hour, and 2-hour post-load glucose and its underlying factors in Hungary in 2010-2017. Design: Cross-sectional analysis of a universal screening program for GDM Setting: 3-point 75g OGTT 24-28 weeks of gestation Population: All singleton pregnant women in Tolna County (South-Western Hungary) in 2010-2017. Methods: All participants with available co-variables and deliveries after 24 weeks of gestation were included (n=7071/8002). Exposures were collected after delivery and included known risk factors of GDM. Main outcome measures: time trends of GDM occurrence (WHO/NICE diagnostic criteria) and fasting, 1-hour, and 2-hour post-load glucose. Analyses were done with multiple logistic and linear regression. Results: The prevalence of GDM increased from 15 to 20% by WHO-GDM in 2010-2017, as well as fasting, 1-hour, and 2-hour post-load glucose (by 0.1, 0.5, 0.2 mmol/l, respectively). Based on our fully adjusted regression models including both BMI measures, a significant proportion (25-30%) of this increase for GDM diagnosis and for fasting glucose was explained by increasing calendar trend in BMI measured at the OGTT. Smaller proportions of 1-hour (12%) and 2-hour (NS) post-load glucose were explained by BMI changes. Conclusions: Our finding suggests that both pre-pregnancy BMI and BMI gain during the first 2 trimesters of pregnancy are important determinants of the GDM epidemic in Hungary. To prevent the further increase in the prevalence of GDM both factors should be targeted.