HbA1c in early pregnancy is a better predictor of gestational diabetes mellitus than fasting and 2h plasma glucose
Afsana, F. (1)*;Bhowmik, B.(2);Hitman, G.A.(3);Khan, A.A.(2);Hussain, A.(2)1Bangladesh Institute of Research and Rehabilitation in Diabetes, Endocrine and Metabolic Disorders, Dhaka, Bangladesh 
2Centre of Global Health Research, Diabetic Association of Bangladesh, Dhaka, Bangladesh
3Barts and The London School of Medicine and Dentistry, Queen Mary University of London, Blizard Institute: 4 Newark Street, London E1 2AT, UK
Background: HbA1c is a widely-used marker in diagnosing type 2 diabetes mellitus (DM), but its clinical utility in screening gestational diabetes mellitus (GDM) is not established.
Aim: To assess the performance of HbA1c in early pregnancy in predicting women at risk of GDM at 24-28 weeks of gestation. 
Method: A total of 861 women participated in a randomized controlled trial conducted in 5 different areas of capital Dhaka, Bangladesh. Fasting (FPG), 2h after 75-gram plasma glucose (2hPG) and HbA1c were estimated at 8-14 weeks of gestation. Among them, 746 women were tested again at 24-28 weeks. Receiver operating characteristic (ROC) curve analysis and logistic regression were performed. GDM was defined following the International Association for Diabetes in Pregnancy Study Group (IADPSG) criteria. 
Results: Among 746 women, 176 (23.6%) women were diagnosed with GDM at 24-28 weeks. 2hPG and HbA1c were significantly higher in women with GDM at 24-28 weeks contrasting against the values at 8-14 weeks of pregnancy. The area under ROC curve of 2hPG and HbA1c for the prediction of GDM were 0.57 (95% CI: 0.51, 0.61) and 0.62 (95% CI: 0.57, 0.67) respectively. HbA1c ≥5.0% at 8-14 weeks was able to predict GDM with sensitivity and specificity of 75.0% and 43.6%. HbA1c (unadjusted OR 2.43, p<0.001 and adjusted 2.38, p<0.001) showed better association with GDM than 2hPG (unadjusted 1.12, p=0.045 and adjusted 1.08, p = 0.205).
Discussion: HbA1c in early pregnancy (8-14 weeks) showed higher sensitivity in predicting GDM than 2hPG for at 24-28 weeks of gestation.