Aim: We wanted to investigate third-trimester HbA1c as a predictor of diabetes after gestational
diabetes mellitus (GDM).
Methods: Women with GDM were followed up prospectively for five years from pregnancy to
detect the development of diabetes. The ability of HbA1c to predict diabetes was evaluated
with receiver-operating characteristic (ROC) curves and logistic regression analysis.
Results: By five years, 73 of 196 women had been diagnosed with diabetes. An optimal cut-off
point for HbA1c of 36mmol/mol (5.4%) could predict diabetes with 45% sensitivity and 92%
specificity. For HbA1c ≥39mmol/mol (≥5.7%), sensitivity, specificity, and positive predictive
value were 30%, 97%, and 91%, respectively. In logistic regression analysis, adjusting for
the diagnostic glucose concentration during pregnancy, HbA1c levels in the upper quartile
(≥36mmol/mol) were associated with a 5.5-fold increased risk of diabetes.
Conclusion: Third-trimester HbA1c levels in the pre-diabetes range revealed women with
post-partum diabetes with high specificity and high positive predictive value. HbA1c testing
could be used as a strategy to select high-risk women for lifestyle interventions aimed
at prevention of diabetes starting during pregnancy. The results should encourage further
validation in other populations using new diagnostic criteria for GDM.