orals Australasian Diabetes in Pregnancy Annual Scientific Meeting 2013

HbA1c in gestational diabetes mellitus (GDM): relationship to the OGTT and pregnancy outcomes (#13)

Lynda Molyneaux 1 , Glynis Ross 1 , Maria I Constantino 1 , Kris Tan 2 , Anna-Jane Harding 1 , Dennis Yue 1 3 , Jencia Wong 1 3
  1. Royal Prince Alfred Hospital Diabetes Centre , Sydney, NSW
  2. Royal Prince Alfred Hospital, Camperdown, NSW, Australia
  3. Sydney Medical School , University of Sydney, Sydney

Background: The HbA1c is used to diagnose diabetes outside pregnancy and provides the best predictor of outcome. Physiological changes in pregnancy can lower HbA1c levels, thus the utility of HbA1c in the diagnosis of GDM is not established and associations with pregnancy outcomes are less clear. We examine the relationship between antenatal HbA1c and post load glucose excursion, antenatal insulin use, obstetric and neonatal outcomes in GDM as a practical guide to its clinical utility.

Methods: Data from 3009 pregnancies complicated by GDM at Royal Prince Alfred Hospital were available for analysis. Clinical and biochemical measures were prospectively collected in a standardised way. The HbA1c measured at the time of GDM diagnosis was analysed in a single laboratory. Relationship of HbA1c and glucose during OGTT was examined. Data were stratified by HbA1c to examine for association.

Results: There is a clear association of increasing HbA1c with increased intervention and poorer pregnancy outcomes. An HbA1c of >5.5% is associated with a higher need for intervention, hypertension, and macrosomia despite treatment, as well as a high rate of diabetes persisting. HbA1c correlates with AUC glucose (r=0.3 p<0.0001) with potential to be used as an OGTT surrogate for diagnosis. However even those with very low HbA1c levels may still require insulin treatment and experience adverse outcomes.

Conclusion: HbA1c threshold levels >5.5% are associated with poorer pregnancy outcome, greater intervention and persisting diabetes. This level identifies the patient with a greater need for surveillance and arguably where limited resources should be prioritised. Despite a correlation between HbA1c and post load glucose, low HbA1c levels do not adequately capture the risks of having GDM. Thus the utility of antenatal HbA1c alone to diagnose GDM is likely to be limited. Whether a screening HbA1c level above 5.5% can reduce the need for OGTT in diagnosis should be explored.

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