First-Trimester A1C as a Tool to Predict the Development of Gestational Diabetes in High-Risk Women

INTRODUCTION: The objective of this study was to determine if hemoglobin A1C drawn with the first prenatal laboratory tests in women at high risk for diabetes is associated with risk of developing gestational diabetes (GDM). We hypothesized that pregnant women with first-trimester impaired glucose tolerance (hemoglobin A1C of 5.7–6.4%) are at an increased risk of developing GDM when compared with women with normal glucose tolerance (hemoglobin A1C of less than 5.7%). METHODS: We conducted a retrospective cohort study in two clinics in Charlotte, North Carolina. We included all women who met the American Diabetes Association guidelines for being at risk of diabetes who had a hemoglobin A1C drawn before 14 weeks of gestation and who did not have overt diabetes (hemoglobin A1C 6.5 or greater). We compared frequency of diagnosis of GDM between patients with a hemoglobin A1C of 5.7–6.4% and those with a hemoglobin A1C less than 5.7% using a χ2 test. RESULTS: Two hundred four women had a hemoglobin A1C drawn at less than 14 weeks of gestation; two were diagnosed with diabetes; 15 had impaired glucose tolerance; and 187 had normal glucose. Fifty percent of women with hemoglobin A1C 5.7–6.4% developed GDM compared with 13.6% of those with hemoglobin A1C less than 5.7% (P=.002). After adjusting for race and history of GDM, women with hemoglobin A1C 5.7–6.4% had more than five times higher odds of developing GDM compared with women with hemoglobin A1C less than 5.7% (odds ratio 5.43, 95% confidence interval 1.69–17.44). CONCLUSIONS: Among women at high risk for diabetes, hemoglobin A1C in the first trimester of pregnancy may predict higher risk and earlier onset of GDM.