310: Is there a mid-trimester Hemoglobin A1c value that excludes Gestational Diabetes?

To determine if there is a cut-off for hemoglobin A1c(HbA1c) that excludes gestational diabetes (GDM). Secondary analysis of a prospective observational study of gravidas undergoing routine screening for GDM at a single tertiary referral center between September 2016 to January 2019. Patient demographics, past medical history, delivery and neonatal information were collected. All patients had a HbA1c and a 1 h glucose screen (GST) collected on the same day as part of routine collection at 24-32 weeks. Exclusion criteria were early GDM diagnosis (< 20 weeks), multiple gestation, and incomplete medical records. GDM was diagnosed by Hba1c > 6.5, 1 h GST > 200, or failed 3 hour glucose tolerance test (GTT). Each HbA1c level was analyzed for sensitivity, specificity, and positive (PPV) and negative (NPV) predictive valve. A secondary analysis was completed to look at risk factors (BMI > 30 kg/m2, GDM in a prior pregnancy, first degree relative with diabetes, and prior fetal macrosomia) and alternation in the predictive value of HbA1c. A total of 979 women had HbA1c and 1 h GST. Forty-four women were diagnosed with GDM. Hba1c had a moderate correlation with the diagnosis of GDM (r = 0.345). All HbA1c’s of 6.2 or higher had GDM. No women with an HbA1c of < 4.5 had GDM. Only 3 cases of GDM were diagnosed with a HbA1c of 5.0 or less. The NPV of a HbA1c of < 5.0 was 99.2% with 40.1% of the population screening negative without undergoing a 1 h GST.(Table 1) Both BMI > 30 and prior GDM increased risk for GDM (p = 0.031 and p< 0.001, respectively). After excluding BMI >30 or prior GDM from the population, no women with an HbA1c < 4.9 had GDM. One case of GDM was diagnosed at HbA1c of less than or equal to 5.0 and the NPV rose to 99.6% (sensitivity 91.6%, specificity 49.1%, PPV: 3.95%). A HbA1c of less than 5.0 is a strong predictor of a negative evaluation for gestational diabetes. In low risk individuals who cannot tolerate or refuse glucose screening, this has the potential to be used as an alternative method of screening.