HbA1c Measured in the First Trimester of Pregnancy and the Association with Gestational Diabetes

We aimed to examine the prospective association between first trimester HbA 1c and gestational diabetes (GDM) and explore the utility of HbA 1c for prediction of GDM. We used data from a case-control study within the prospective NICHD Fetal Growth Studies-Singleton Cohort (2009–2013), which enrolled 2,802 women at 12 U.S. clinical centers. HbA 1c was measured in GDM cases (n = 107) and matched controls (n = 214) targeted at 8–13, 16–22, 24–29, and 34–37 gestational weeks. We excluded women with HbA 1c ≥ 6.5% (48 mmol/mol) at enrollment (n = 3) or who had a hemoglobin variant (n = 6). At 8–13 gestational weeks, women who later developed GDM had significantly higher HbA 1c (5.3[standard deviation 0.3]%; 34[4]mmol/mol) than women without GDM (5.1[0.3]%; 32[3] mmol/mol) (P ≤ 0.001); this difference remained significant throughout pregnancy. Each 0.1% (1 mmol/mol) HbA 1c increase at 8–13 weeks was associated with an adjusted 22% increased GDM risk (95% confidence interval 1.09–1.36). First trimester HbA 1c significantly improved GDM prediction over conventional risk factors (AUC 0.59 vs 0.65; P = 0.04). In conclusion, women who develop GDM may have impaired glucose homeostasis early in or prior to pregnancy, as indicated by their elevated first trimester HbA 1c . First trimester HbA 1c may aid in early identification of at risk women.