Identifying Characteristics of Antenatal 3-Hour GTT as Markers for Abnormal Postpartum Glucose Tolerance [20I

Abstract

INTRODUCTION: GDM is diagnosed on the basis of blood glucose levels that exceed specific glycemic thresholds. We sought to identify characteristics of antenatal glucose testing that may serve as markers for abnormal postpartum testing. METHODS: IRB approved retrospective cohort study. A database was created from all women who underwent a postpartum 2-hour oral glucose tolerance test at the Carolinas Medical Center Diabetes Clinic in Charlotte, NC between 2012-2015. Inclusion criteria: singleton pregnancy, diagnosis of GDM, postpartum GTT completed 4-12 weeks post-partum. GDM was diagnosed by at least 2 elevated values on a completed 3-hour glucose tolerance test (Carpenter-Coustan). Data was indexed using two methods: clinical groups and by number of abnormal values. Four groups were defined: Group A; abnormal fasting value. Group B; all values < 200mg/dl. Group C; Any value ≥200mg/dl. Group D; Both an elevated fasting AND any value ≥200mg/dl. Patients were also grouped according to the number of abnormal values on 3h GTT; either 2, 3 or 4 abnormal values. Chi-square or Mantel-Haenszel tests were used for categorical variables. T-tests and generalized linear models were used for continuous variables. Poisson regression models were used to calculate relative risks (RR) and 95% confidence intervals. RESULTS: 407 patients met study criteria. 57% were diagnosed with abnormal 2-hour postpartum glucose tolerance (PGT). Groups A, C, and D had a greater RR of abnormal 2-hour PGT compared to Group B. Four abnormal values on 3-hour antenatal GTT compared with two abnormal values was associated with a higher risk of abnormal PGT. These results are not statistically significant. CONCLUSION: No statistically significant markers for abnormal PGT identified from the antenatal 3-hour GTT. The population in our study represents patients compliant with post-partum glucose tolerance testing. Our results may have been affected because patients with poor control of GDM are less likely to be compliant with postpartum glucose tolerance testing.