189: What is the optimal Hemoglobin A1c screening cut-off for the prediction of gestational diabetes mellitus?

Abstract

To identify a Hemoglobin A1c (HbA1c) value on universal screening that best predicts the development of gestational diabetes mellitus (GDM). This is a retrospective cohort study of women who underwent HbA1c screening at first prenatal visit < 17 weeks’ gestation between December 2016 and April 2018 at a single urban tertiary care center. Women with preexisting diabetes, multiple gestation, hemoglobinopathy, fetal demise, and no glucose tolerance screening were excluded. Women with HbA1c values < 5.7% underwent routine two-step GDM screening. Women with impaired glucose tolerance, HbA1c of 5.7 – 6.4%, were asked to undergo two-step GDM screening upon receipt of their results. Positive screens were diagnosed with early GDM. Women with normal early screening underwent repeat 3rd trimester screening. The optimal HbA1c cutoff point was defined as the value of HbA1c for which the sum of sensitivity and specificity was the highest. We assessed the predictive ability of the cutoff points HbA1c ≥ 5.4% and HbA1c ≥ 5.7% with receiver operative curves (ROCs) and compared their respective areas under the curve (AUC). 3072 women had universal HbA1c screening, and 1921 women met inclusion criteria. Clinical characteristics are presented in Table 1. There was a continuous relationship between HbA1c and GDM development (AUC = 0.698, 95%CI 0.65-0.75). The optimal HbA1c screening value was 5.4%, with a sensitivity and specificity of 69.7% and 60.2%, respectively. The negative predictive value (NPV) was 96.4%; the positive predictive value (PPV) was 11.4%. In comparison, the sensitivity and specificity of HbA1c > 5.7% were 35.61% and 89.4%, respectively. The NPV was 95% and PPV was 19.8%. After adjusting for race, age, insurance status, and body mass index (BMI), the AUCs for HbA1c > 5.4% and > 5.7% were 0.747 and 0.745, respectively (p = 0.862) HbA1c > 5.4% on universal screening is the optimal predictor for GDM. However, it performs similarly to the clinically accepted cutoff of HbA1c > 5.7% after controlling for potential confounders.View Large Image Figure ViewerDownload Hi-res image Download (PPT)