First-trimester HbA1c as a predictor of gestational diabetes mellitus: A prospective cohort study

Abstract

Gestational Diabetes Mellitus (GDM) is a common and increasing pregnancy complication in Ethiopia, with marked subnational variation. Early identification of high-risk women remains challenging. The predictive value of first-trimester glycated hemoglobin (HbA1c) for GDM has not been well studied in this population. A prospective observational cohort study was conducted at two public health centers in Addis Ababa, Ethiopia. A total of 157 pregnant women without pre-existing diabetes were enrolled in the first-trimester. HbA1c was measured at enrollment (<13 weeks of gestation), and GDM was diagnosed at 24–28 weeks using a 75-g Oral Glucose Tolerance Test (OGTT) according to IADPSG criteria. Predictive performance was assessed using receiver operating characteristic (ROC) curve analysis, and independent predictors were identified using logistic regression. The incidence of GDM was 29.3% (46/157). First-trimester HbA1c levels were significantly higher among women who later developed GDM (5.61% ± 0.24% vs. 5.30% ± 0.26%, P < 0.001). An HbA1c cut-off of approximately 5.1% demonstrated high sensitivity (97.8%) and a negative predictive value of 96.8%. A graded, dose–response relationship was observed, with increasing GDM incidences across higher HbA1c categories. Notably, all women with first-trimester HbA1c ≥ 5.91% developed GDM. External Validation of the STRIDE-Kenya prediction model demonstrated improved performance compared with HbA1c alone, with a higher AUC (0.844 vs. 0.810), improved specificity (74.8% vs. 57.7%), and a greater Youden’s index (0.596 vs. 0.425). First-trimester HbA1c is a strong and independent predictor of GDM in this Ethiopian cohort. Its high NPV suggests it may be useful for identifying women at low risk, while elevated levels can stratify women at higher risk for closer surveillance and early intervention.