Screening for gestational diabetes by measuring fasting plasma glucose levels

Abstract

Objectives: (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.

Methods: 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.

Results: 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.

Conclusion: 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.

Keywords: fasting plasma glucose levels; gestational diabetes; pregnancy; screening.

Figure 1

Distribution of negative and positive GDMs using fasting blood sugar testing under the receiving operating characteristics curve

Figure 2

Sensitivity and specificity of fasting plasma glucose in detecting gestational diabetes mellitus

Figure 3

Receiver operating characteristics (ROC) curve of fasting plasma glucose concentration.