Hemoglobin A1C as a Diagnostic Test for Gestational Diabetes [17C

Abstract

INTRODUCTION: ACOG recommends gestational diabetes mellitus (GDM) testing using a 1-hour 50-gram oral glucose challenge test (24–28 weeks gestation) and if elevated (>140 mg/dL), a 3-hr 100-gram oral glucose tolerance test. Objective was to determine if HbA1c testing can replace ACOG guidelines, offering a more tolerable, less time-consuming test for GDM. METHODS: This is a prospective cohort study of patients presenting <14 weeks gestation for prenatal care between 11/2011 and 6/2014. HbA1c levels obtained at initial visit and 24–28 weeks gestation were compared between patients with and without GDM and tested as a replacement for ACOG guidelines. RESULTS: Study was comprised of 146 of 364 consented patients meeting inclusion criteria (mean age: 25 years, obesity: 41.5%, and DM family history: 50%). Initial HbA1c values compared to 24–28 weeks revealed a small but significant decrease (5.2 vs 5.1, P<.001). However, mean HbA1c levels were higher in patients with GDM (5.3 vs 5.1, P=.027). Elevated HbA1c (>5.5) and positive GDM showed significant, but weak agreement (Kappa=0.69, P=.041), (sensitivity: 25% and specificity: 92.5%). ROC curve analysis determined optimal threshold 5.15 yielding sensitivity: 66.7%; specificity: 66.4%, PPV: 15.1%, and NPV: 95.7%. Analysis of mean change from initial to 24–28 HbA1c resulted in no main effect for GDM, but a significant GDM by HbA1c interaction (P=.002). GDMA patients demonstrated increased mean HbA1c and non-diabetics decreased mean HbA1c. CONCLUSION: While our data showed that patients with GDM had elevated levels of HbA1c at 24–28 weeks gestation, this test is not a reliable replacement for ACOG guidelines.