Overweight and obese pregnant woman are known to be at increased risk of developing gestational diabetes. However, little is known about early screening in this population. The objective of this study was to determine early (< 20 gestational age) hemoglobin A1c values between overweight and obese pregnant women who develop gestational diabetes (GDM) compared those who do not develop GDM. A case-control study comparing overweight and obese women with GDM to overweight and obese women without GDM (non-GDM) in a 3:1 ratio between 2011 and 2014 at Oregon Health and Sciences University to determine if early hemoglobin A1C (HbA1C; obtained < 20 weeks gestational age) differs between the two cohorts. Chi squared, Pearson correlation, and Wilcoxon rank-sum test were used to compare GDM and non-GDM pregnancies. Receiver Operating Characteristic (ROC) curve was analyzed to plot the true positive rate against the false positive rate for the different possible cut-points of early HbA1C to predict the diagnosis of GDM among overweight and obese women. A total of 443 subjects were analyzed (n=139 cases and n=304 controls). Women with GDM were more likely to be non-white, older in age, multiparous and have a higher pre-pregnancy BMI (see Table). Women with GDM had a significant difference in early HbA1C compared to non-GDM pregnancies (5.6 and 5.3%, P<0.01). Early HbA1C is more significantly correlated with GDM diagnosis than pre-pregnancy BMI (0.34 vs 0.13; p<0.01). The curve point at which the area under the ROC curve was maximized was an early HbA1C of 5.6% with an AUC = 0.725 (see Figure). Overweight and obese women who develop GDM have significantly different HbA1C than non- GDM pregnancies. The mean HbA1C is lower than the American Diabetes Association definition for pre-diabetes. When using A1c as a screening tool, these data suggest lower cut-points should be considered among overweight and obese pregnant women to perform early diagnostic diabetes testing in pregnancy. However, further studies are needed to determine a reliable, predictive HbA1C.View Large Image Figure ViewerDownload Hi-res image Download (PPT)