Fasting plasma glucose as a screening test for gestational diabetes in a multi-ethnic, high-risk population

Screening every pregnant woman for gestational diabetes mellitus (GDM), as widely recommended for high-incidence populations, strains the healthcare system excessively. This study investigated the value of fasting plasma glucose (FPG) as an alternative to the more cumbersome oral glucose tolerance test (OGTT).

One thousand six hundred and forty-four pregnant women in a multi-ethnic, high-risk population were evaluated by the FPG as a screening test among two principal subgroups, i.e. women (n = 1276) at risk for GDM on clinical grounds and those women (n = 368) with a positive post 50-g, 1-h plasma glucose challenge test (GCT). Two threshold values for FPG 'ruled in or ruled out' a GDM diagnosis, which was confirmed by the 3-h, 100-g OGTT, using Carpenter's modified criteria as the 'gold standard'.

In the women with a positive clinical history, at an optimal cut-off value of FPG < 4.4 mmol/l to rule out GDM; a sensitivity of 94.7% was achieved, 21 (1.6%) women being false negatives. Using a FPG > or = 5.3 mmol/l to rule in GDM; the specificity was 94.0% with 53 (4.2%) women being classified as false positives. FPG would have eliminated need for the OGTT in 50.9% pregnant women (misclassification rate 5.8%). In the positive GCT group, using similar cut-offs for FPG, a sensitivity of 96.6% and specificity of 90.8% was achieved with a potential to avoid 51.6% OGTTs (misclassification rate 7.3%). The positive predictive value of the GCT was 31.8% compared to 80.2% for FPG at 5.3 mmol/l.

While previously neglected as a screening test for GDM, in selected high-risk populations the FPG offers a potentially simple, practical algorithm to screen for GDM by being cost-effective and patient friendly. A wider application should be explored.