Recent New Zealand guidelines recommend annual glycated haemoglobin (HbA1c) measurements from three months postpartum, replacing the glucose tolerance test (GTT) at six weeks, to screen for persistent hyperglycaemia following gestational diabetes. Data suggest that this screening approach may miss cases of type 2 diabetes, but are they detected at subsequent screening and will screening rates improve?

Our aim was to evaluate the effectiveness of HbA1c monitoring in improving screening rates following gestational diabetes and in detecting postpartum hyperglycaemia.

Materials and Methods
During 2015 in Christchurch, all women with gestational diabetes were offered HbA1c and GTT measurements at three months postpartum and subsequent annual HbA1c measurements were recommended. Data from electronic hospital records were collected for a minimum 18 months postpartum.

Of the cohort of 333 women, 218 (65%) completed both HbA1c and GTT at three months postpartum, 74 (22%) HbA1c only, 16 (5%) GTT only, 25 (8%) no screening; 184 (55%) had subsequent HbA1c tests. Diabetes was detected by GTT in five (2%) women and by HbA1c in only one out of five (20%); the disagreement between tests resolved in three out of four (75%) women with subsequent testing. Prediabetes was detected by GTT in 30 (14%) women; however, HbA1c only detected five out of 30 (17%) and subsequent HbA1c testing identified a further two out of 30 with prediabetes.

HbA1c measurement at three months postpartum had a good uptake. However, most cases of diabetes were identified by subsequent HbA1c testing, the uptake of which was suboptimal. The importance of annual HbA1c monitoring following gestational diabetes needs greater emphasis.