Screening for gestational diabetes: a retrospective audit

There are various indications for screening pregnant women for gestational diabetes. Screening is then often carried out by performing a timed random blood sugar (t-RBS). In this unit a raised t-RBS is an indication to perform a glucose tolerance test (GTT), and if this is abnormal, the patient is managed with dietary modification or insulin therapy. A t-RBS is considered abnormal if the fasting value (> 2 hours since last meal) is > 5.7 mmol/l, or the non-fasting value (<2 hours since last metal) is > 6.3 mmol/l. However, higher t-RBS values have been recommended by the Diabetic Pregnancy Study Group. This group considers a t-RBS abnormal if the fasting value is > 6.1 mmol/l, or the non-fasting value is > 7.0 mmol/l. A retrospective audit was carried out to determine if cases of gestational diabetes would have been missed if the new guidelines were adopted. There were 112 patients with a fasting t-RBS of 5.8 to 6.1 mmol/l, inclusive, and 196 patients with a non-fasting t-RBS of 6.4 to 7.0 mmol/l, inclusive; 45 patients did not have a GTT result. Therefore 263 patients were included in the study. The number of patients with a normal GTT result was 257 (97.7%), and 6 (2.30%) patients had an abnormal GTT result. Only 4 (1.52%) were labelled as gestational diabetics, and all these cases were managed with diet alone with no adverse obstetric outcome. A large number of GTTs are performed unnecessarily in our unit, and the values recommended by the Diabetic Pregnancy Study Group should be adopted.