Value of HbA1c in Obese Women with Gestational Diabetes

Abstract

Objective: We sought to assess the association of hemoglobin A1c (HbA1c) with adverse perinatal outcomes in obese women with gestational diabetes mellitus (GDM). Study Design: This was a secondary analysis of a multicenter randomized controlled trial assessing early (14–20 weeks) versus routine (24–28 weeks) screening for GDM in obese women. Women were included if they were diagnosed with GDM at either time during pregnancy and had a HbA1c result available. The primary exposure was HbA1c at 24 to 28 weeks. The primary outcome was a composite of macrosomia, primary cesarean, pregnancy-induced hypertension, shoulder dystocia, neonatal hypoglycemia, or hyperbilirubinemia. Receiver operating characteristics (ROC) curves were used to assess the association of HbA1c with the composite outcome. The Liu method was used to select an optimal HbA1c cutoff, and the incidence of the outcome compared. Results: Of 125 women with GDM, 93 (74%) had a HbA1c at 24 to 28 weeks and 103 (82.4%) had a HbA1c at 14 to 20 weeks. Baseline characteristics were balanced between groups above and below the cutoff. The area under the ROC curve for HbA1c and its association with the adverse perinatal composite outcome was 0.6 (95% confidence interval [CI]: 0.5–0.7). The frequency of the primary outcome was similar among women with low and high HbA1c at 24 to 28 weeks (adjusted relative risk, 1.12, 95% CI: 0.97–1.29). Compared with women with a decreasing HbA1c during pregnancy, women with a stable or increasing HbA1c did not have a significant increase in the primary adverse perinatal composite outcome. However, the frequency of preterm delivery was higher among women with stable or increasing HbA1c compared with those with a decreasing HbA1c (26.1 vs. 6.7%, p = 0.03). Conclusion: A single HbA1c in women with GDM is not associated with a composite perinatal adverse outcome, but a HbA1c that increases or remains stable between 14 to 20 and 24 to 28 weeks is associated with an increase in preterm delivery. Key Points