First Trimester Hemoglobin A1c Prediction of Gestational Diabetes.

Objective The objective of this study is to examine whether a first trimester hemoglobin A1c (A1C) of 5.7 to 6.4% predicts an abnormal second trimester oral glucose tolerance test (OGTT). Methods We conducted a retrospective cohort study of all women screened with A1C through 13 (6/7) weeks' gestation between January 1, 2011, and December 31, 2012. Prediabetic women (A1C of 5.7-6.4%) were compared with women with a normal first trimester A1C (< 5.7%). The primary outcome was an abnormal 2-hour, 75-g OGTT as defined by the International Association of Diabetes and Pregnancy Study Groups. Results There were 2,812 women who met inclusion criteria of whom 6.7% (n = 189) were prediabetic. Women with prediabetes were more likely to have gestational diabetes mellitus (GDM) even after adjusting for potential confounders (29.1 vs. 13.7%; adjusted relative risk, 1.48; 95% confidence interval, 1.15-1.89). There were no statistically significant differences in secondary outcomes except that women with prediabetes had less excessive gestational weight gain. A prediabetic-range A1C in the first trimester was associated with a 13% sensitivity and a 94% specificity for predicting GDM Conclusion Although women with prediabetes by first trimester A1C are significantly more likely to have GDM, the low sensitivity of an A1C in this range renders it a poor test to identify women who will develop GDM.