Is omitting the 3rd hour measurement in the 100 g oral glucose tolerance test feasible?

Abstract

To evaluate the diagnostic value of the 3rd hour plasma glucose level in the 100 g oral glucose tolerance test (OGTT). Records of all pregnant patients with abnormal 50 g glucose challenge test (GCT) between January 2005 and December 2013 were reviewed (n=1963). The 100 g OGTT results were analyzed separately for both Carpenter & Couston (CC) and National Diabetes Data Group (NDDG) criteria. The number of patients diagnosed with gestational diabetes mellitus (GDM) was 297 (15.1%) according to CC criteria and 166 (8.4%) according to NDDG criteria. The 1st hour plasma glucose level showed the highest correlation with GDM diagnosis (ρ=0.595 for CC and ρ=0.567 for NDDG). However, the 3rd hour plasma glucose level showed the weakest correlation with GDM diagnosis (ρ=0.216 for CC and ρ=0.213 for NDDG). The 3rd hour value of 100 g OGTT was one of the two elevated measurements in 10.8% of patients when CC criteria are used and in 13.8% of patients when NDDG criteria are used. Omitting 3rd hour plasma glucose measurement in 100 g OGTT results in unacceptable rates of underdiagnosed patients.