Fasting Capillary Glucose as a Screening Test for Ruling Out Gestational Diabetes Mellitus

Abstract Objective A common approach to screening for gestational diabetes mellitus (GDM) is the testing of all pregnant women with a one-hour, 50 g glucose challenge test (GCT), followed by a diagnostic oral glucose tolerance test (OGTT) when the GCT is positive (≥ 7. 8 mmol/L). As only a small subset of those with a positive GCT will have GDM, many more women undergo the OGTT than may be necessary. In this context, we hypothesized that measurement of fasting capillary glucose (FCG) could provide a strategy for reducing the number of unnecessary OGTTs. Thus, we sought to identify a threshold level of FCG below which GDM could be ruled out following a positive GCT, without need for the OGTT. Methods Following a positive GCT, 888 women underwent measurement of FCG prior to their OGTT. We evaluated the test characteristics of FCG for identifying the 209 women diagnosed with GDM on the OGTT. Results Fasting capillary glucose was positively associated with each glucose measurement on the OGTT (all P < 0.001) and inversely related to insulin sensitivity and pancreatic beta-cell function (both P < 0. 001). As FCG increased, the prevalence of GDM progressively rose ( P < 0. 001). However, the area under the curve of the receiver-operating characteristic curve for FCG in predicting GDM was modest (0.67). Although using an FCG threshold of 4.8 mmol/L could reduce the number of OGTTs by 28.4%, this approach would miss 18.2% of cases of GDM. Conclusion Fasting capillary glucose is associated with glycemia, insulin sensitivity, and pancreatic beta-cell function. However, a single FCG measurement is insufficient for reliably ruling out GDM after an abnormal GCT.