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 GDMConclusion
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.