Objective: Previous gestational diabetes (GDM) is associated with a significant lifetime risk of type 2 diabetes. In this study, we assessed the performance of HbA1c and fasting plasma glucose (FPG) measurements against that of 75 g oral glucose tolerance testing (OGTT) for the follow-up screening of women with previous GDM.
Methods: Two hundred and sixty-six women with previous GDM underwent the follow-up testing (mean of 2.6 years (s.d. 1.0) post-index pregnancy) using HbA1c (100%), and 75 g OGTT (89%) or FPG (11%). American Diabetes Association (ADA) criteria for abnormal glucose tolerance were used.
Design, cohort study, and results: The ADA HbA1c high-risk cut-off of 39 mmol/mol yielded sensitivity of 45% (95% CI 32, 59), specificity of 84% (95% CI 78, 88), negative predictive value (NPV) of 87% (95% CI 82, 91) and positive predictive value (PPV) of 39% (95% CI 27, 52) for detecting abnormal glucose tolerance. ADA high-risk criterion for FPG of 5.6 mmol/l showed sensitivity of 80% (95% CI 66, 89), specificity of 100% (95% CI 98, 100), NPV of 96% (95% CI 92, 98) and PPV of 100% (95% CI 91, 100). Combining HbA1c ≥39 mmol/mol with FPG ≥5.6 mmol/l yielded sensitivity of 90% (95% CI 78, 96), specificity of 84% (95% CI 78, 88), NPV of 97% (95% CI 94, 99) and PPV of 56% (95% CI 45, 66).
Conclusions: Combining test cut-offs of 5.6 mmol/l and HbA1c 39 mmol/mol identifies 90% of women with abnormal glucose tolerance post-GDM (mean 2.6 years (s.d.1.0) post-index pregnancy). Applying this follow-up strategy will reduce the number of OGTT tests required by 70%, will be more convenient for women and their practitioners, and is likely to lead to increased uptake of long-term retesting by these women whose risk for type 2 diabetes is substantially increased.