Can an Early GCT Value and A1C Eliminate the Need for Repeat GCT Testing during Second-Trimester Pregnancy?

Background: While A1c is a widely used marker for IDDM and NIDDM, its clinical use in gestational diabetes mellitus (GDM) is not well elucidated. We aimed to evaluate if an A1c and an early glucose challenge test (GCT) can be used to identify patients who may forgo repeat 2nd trimester GCT testing. Methods: This was a retrospective cohort study of patients eligible for early GDM screening who had a negative screening at ≤20 weeks gestation and delivered at a single center between 2016-2020. The primary outcome was GDM in the 2nd trimester by Carpenter & Coustan criteria. Receiver operating characteristic (ROC) curve analyses were performed to compare the ability of early GCT value, and in combination with A1c to predict the primary outcome. Results: Of the 2,025 patients eligible for early GDM screening, 722 met inclusion criteria. Of these, 583 had a 1-hour GCT, 178 had an A1c, and 38 had both. The prediction of GDM diagnosis in the 2nd trimester using an early GCT value, A1c, and both on a ROC plot produced an area under the curve (AUC) of 0.753, 0.659, and 0.672, respectively. The highest A1c where no patients were diagnosed with GDM in 2nd trimester was 4.5%, but of the 43 patients with A1c ≤5.1%, 1 (2.3%) was diagnosed with GDM in the 2nd trimester. Conclusion: Early GCT value alone was a better predictor of GDM in 2nd trimester than a combination of GCT with A1c. A1c alone was a poor predictor. Disclosure J.A.Beacham: None. K.C.Bodycot: None. R.Huang: None. H.B.Al-kouatly: None. R.Mclaren: None.