Background and aim: Women with a history of gestational diabetes mellitus (GDM) are at increased risk for type 2 diabetes (T2D). It is thus recommended that an oral glucose tolerance test (OGTT) be performed after delivery. Recently, the use of glycated haemoglobin A1c (HbA1c) has been proposed as a simpler and faster method to diagnose glucose disorders. The aim of this study was to investigate whether HbA1c measurement can replace OGTT in the detection of prediabetes and T2D in women with a history of GDM.
Patients and methods: We studied 1336 women (35.3 ± 5.8 years old) with a history of GDM 16.6 ± 28.2 months after delivery. All women were evaluated through an OGTT and a simultaneous HbA1c measurement. American Diabetes Association (ADA) criteria were used for the assessment of glucose disorders. Sensitivity and specificity of HbA1c were measured for the prediction of T2D and prediabetes, while Cohen's coefficient of agreement (k) was calculated. ROC analysis was performed to evaluate the sensitivity and specificity of HbA1c.
Results: Based on OGTT, 725 women (54.3%) were normal, 406 (30.4%) presented impaired fasting glucose (IFG), 48 (3.6%) impaired glucose tolerance (IGT), 74 (5.5%) combined IFG+IGT, and 83 presented with T2D (6.2%). By contrast, using HbA1c as a screening test, 1150 women (94.1%) were normal, while 49 (4.0%) had prediabetes and 23 (1.9%) T2D. Sensitivity of HbA1c for the diagnosis of prediabetes was 5.3% in comparison to OGTT, specificity was 99.2%, while for the diagnosis of T2D, the percentages were 29.6 and 100%, respectively. The consistency in classifying impaired glucose tolerance between HbA1c and OGTT was 59.7%. Cohen's coefficient of agreement was k = 0.116, indicating slight agreement. Performing a ROC curve, the optimal value of distinctive ability of HbA1c was 4.6% in the case of prediabetes, while for diabetes, it was 5.5%.
Conclusion: This study provided evidence that HbA1c can identify fewer women with prediabetes and T2D than OGTT, indicating that HbA1c cannot be recommended as an alternative post-pregnancy screening method.
Keywords: Diabetes; Gestational; HbA1c; OGTT; Prediabetes.