Screening for gestational diabetes by measuring fasting plasma glucose levels

(a) To test the sensitivity and specificity of measuring fasting plasma glucose levels (FPG) as a screening test for gestational diabetes mellitus (GDM). (b) To compare predicting levels of FPG levels with the one-hour, oral 50g non-fasting glucose challenge test (GCT) for predicting GDM.

One thousand and six hundred pregnant women from the Health Centres, antenatal clinics and Salmaniya Medical Complex were screened by the GCT after 50g of oral glucose during 26-32 weeks gestation, giving a 13.5% incidence of GDM (using the Third International Workshop cutoff values of 7.8 mmol /l). All patients also had an FPG estimation followed by the three-hour oral glucose tolerance test (oGTT). Seventy eight percent of the patients were Bahraini, 19% Asian and 3% other nationalities. Their mean age was 27.2+0.2 years. Receiver-operating curves (ROC) were used to test the ability of the FPG and the oGTT to differentiate patients with GDM and identify the cut off values for predicting a diagnosis of GDM.

FPG levels of 5.6 mmol /l and 5.4 mmol /l yielded sensitivities and specificities of 94% and 93% respectively. Measuring FPG as a screening test required a diagnostic oGTT in 32% compared with 13% when the GCT was used.

Using FPG levels at a cutoff value of ≥ 5.5 mmol /l is an easier, more acceptable test for patients compared to the GCT. Using the FPG levels is also more cost effective and allows nearly 70% of women to avoid the oGTT.