External Evaluation of an Early Pregnancy Hba1c-Based Strategy for Gestational Diabetes Screening in an Indian Hospital Population

Background: Early pregnancy HbA1c has been proposed as a simple screening tool to reduce the need for oral glucosetolerance testing (OGTT). This study evaluated previously proposed HbA1c rule-out and rule-in thresholds in an Indianhospital population. Materials and Methods: This secondary analysis included 100 pregnant women. First-trimester HbA1cwas evaluated against recorded GDM and reconstructed IADPSG positivity. Diagnostic performance was assessed at HbA1cthresholds from 4.9% to 6.5%. A two-threshold strategy using <4.9% for rule-out, 4.9–5.39% as the OGTT zone and ≥5.4%for rule-in was also assessed. ROC analysis was performed. Results: HbA1c showed modest discrimination for recordedGDM (AUC 0.635, 95% CI 0.524–0.747) and poor discrimination for IADPSG positivity (AUC 0.518, 95% CI 0.395–0.642). At ≥4.9%, sensitivity and specificity for recorded GDM were 76.1% and 37.0%, respectively. The two-thresholdstrategy classified 31 women as rule-out, four in the OGTT zone and 65 as rule-in. Although OGTT could theoretically beavoided in 96%, 11 women with recorded GDM and 21 IADPSG-positive women were present in the rule-out group.Conclusion: Early pregnancy HbA1c showed limited stand-alone screening performance. The proposed two-thresholdstrategy reduced theoretical OGTT requirement but resulted in substantial misclassification. External validation is requiredbefore such thresholds are used in routine practice.