Understanding the Utility of Hemoglobin A1c in Diagnosing Gestational Diabetes in Early Pregnancy

In this retrospective cohort study of 243 pregnant women who had combined hemoglobin A1c (HbA1c) and a two-step oral glucose tolerance testing at less than 21 weeks of gestation, median values of HbA1c were higher in women with gestational diabetes compared to nondiabetics (5.8% compared to 5.3%; P < 0.001). The predictive probability of using HbA1c in diagnosing diabetes in early pregnancy was high compared to two-step testing (area under the curve, 0.8), with an optimal diagnostic threshold of 5.6%. Although a HbA1c level of > 6.5% is diagnostic of early gestational diabetes, a lower diagnostic threshold might be justified during pregnancy.