Baseline HbA1c to Identify High-Risk Gestational Diabetes: Utility in Early vs Standard Gestational Diabetes.

Context: The increasing prevalence of gestational diabetes mellitus (GDM) necessitates risk stratification directing limited antenatal resources to those at greatest risk. Recent evidence demonstrates that an early pregnancy glycated hemoglobin (HbA1c ≥5.9% (41 mmol/mol) predicts adverse pregnancy outcomes. Objective: To determine the optimal HbA1c threshold for adverse pregnancy outcomes in GDM in a treated multiethnic cohort and whether this differs in women diagnosed <24 vs ≥24 weeks' gestation (early vs standard GDM). Design and Setting: This was a retrospective cohort study undertaken at the Royal Prince Alfred Hospital Diabetes Antenatal Clinic, Australia, between 1991 and 2011. Patients and Interventions: Pregnant women (N = 3098) underwent an HbA1c (single-laboratory) measurement at the time of GDM diagnosis. Maternal clinical and pregnancy outcome data were collected prospectively. Main Outcome Measure: The association between baseline HbA1c and adverse pregnancy outcomes in early vs standard GDM. Results: HbA1c was measured at a median of 17.6 ± 3.3 weeks' gestation in early GDM (n = 844) and 29.4 ± 2.6 weeks' gestation in standard GDM (n = 2254). In standard GDM, HbA1c >5.9% (41 mmol/mol) was associated with the greatest risk of large-for-gestational-age (odds ratio [95% confidence interval] = 2.7 [1.5-4.9]), macrosomia (3.5 [1.4-8.6]), cesarean section (3.6 [2.1-6.2]), and hypertensive disorders (2.6 [1.1-5.8]). In early GDM, similar HbA1c associations were seen; however, lower HbA1c correlated with the greatest risk of small-for-gestational-age (P trend = 0.004) and prevalence of neonatal hypoglycemia. Conclusions: Baseline HbA1c >5.9% (41 mmol/mol) identifies an increased risk of large-for-gestational-age, macrosomia, cesarean section, and hypertensive disorders in standard GDM. Although similar associations are seen in early GDM, higher HbA1c levels do not adequately capture risk-limiting utility as a triage tool in this cohort.