Background: We have previously found poor agreement between post-partum HbA1c and 75g Oral Glucose Tolerance Test (OGTT) results following a gestational diabetes (GDM) pregnancy1. Amongst 114 women with GDM, only 54% of paired results were in agreement for normal glucose tolerance, pre-diabetes, or diabetes. HbA1c was more likely to diagnose a greater degree of glucose intolerance. We now aim to determine if there is improved agreement between HbA1c and OGTT results 1 to 3 years later.
Methods: Women with disagreement between HbA1c and OGTT results 6 to 12 weeks post-partum are the subjects of the current study. WHO criteria was used for the OGTT diagnosis of diabetes and pre-diabetes. Using the American Diabetes Association criteria, diabetes was defined as HbA1c ≥ 6.5% and pre-diabetes as HbA1c 5.7% to 6.4%. Women underwent repeat OGTT and HbA1c testing 1 to 3 years post-partum. Changes in agreement were analysed using McNemar’s test.
Results: Of the 55 women who originally had disagreement between OGTT and HbA1c results, 21 agreed to repeat testing. Following a mean of 26±8 months post-partum, there was a significant improvement in agreement between HbA1c and OGTT results, with 14 out of 21 women (67%) now showing agreement (p<0.001). Overall there was an improvement in glucose tolerance, defined by either OGTT or HbA1c criteria. There was a significant reduction in HbA1c, from 5.9±0.4%, 6 to 12 weeks post-partum, to 5.5±0.4%, 1 to 3 years later (p<0.001). The HbA1c diagnosed a higher category of glucose intolerance than the OGTT in only 4 patients (19%) on repeat testing, compared to 15 patients (71%) immediately postpartum (p<0.001).
Conclusion: There is poor agreement between the OGTT and HbA1c for the diagnosis of diabetes and pre-diabetes immediately post-partum. However, the agreement between the tests improves substantially 1 to 3 years post-partum.