An Early Pregnancy HbA1c ≥5.9% (41 mmol/mol) Is Optimal for Detecting Diabetes and Identifies Women at Increased Risk of Adverse Pregnancy Outcomes

OBJECTIVE Pregnant women with undiagnosed diabetes are a high-risk group that may benefit from early intervention. Extrapolating from nonpregnancy data, HbA 1c ≥6.5% (48 mmol/mol) is recommended to define diabetes in pregnancy. Our aims were to determine the optimal HbA 1c threshold for detecting diabetes in early pregnancy as defined by an early oral glucose tolerance test (OGTT) at RESEARCH DESIGN AND METHODS During 2008–2010 in Christchurch, New Zealand, women were offered an HbA 1c measurement with their first antenatal bloods. Pregnancy outcome data were collected. A subset completed an early OGTT, and HbA 1c performance was assessed using World Health Organization criteria. RESULTS HbA 1c was measured at a median 47 days’ gestation in 16,122 women. Of those invited, 974/4,201 (23%) undertook an early OGTT. In this subset, HbA 1c ≥5.9% (41 mmol/mol) captured all 15 cases of diabetes, 7 with HbA 1c 1c threshold was also 98.4% (95% CI 97–99.9%) specific for gestational diabetes mellitus (GDM) before 20 weeks (positive predictive value = 52.9%). In the total cohort, excluding women referred for GDM management, women with HbA 1c of 5.9–6.4% (41–46 mmol/mol; n = 200) had poorer pregnancy outcomes than those with HbA 1c n = 8,174): relative risk (95% CI) of major congenital anomaly was 2.67 (1.28–5.53), preeclampsia was 2.42 (1.34–4.38), shoulder dystocia was 2.47 (1.05–5.85), and perinatal death was 3.96 (1.54–10.16). CONCLUSIONS HbA 1c measurements were readily performed in contrast to the low uptake of early OGTTs. HbA 1c ≥5.9% (≥41 mmol/mol) identified all women with diabetes and a group at significantly increased risk of adverse pregnancy outcomes.