Which cutoff level should be used in screening for glucose intolerance in pregnancy?

Abstract

OBJECTIVE: Our purpose was to examine the validity of 140 mg/dL cutoff value in oral glucose challenge test screening for gestational diabetes mellitus when including in the group to be identified women fulfilling more inclusive Carpenter and Coustan criteria for 100-g oral glucose tolerance testing interpretation and gravid women with borderline glucose intolerance. STUDY DESIGN: We reanalyzed data of a multicenter study performed on 704 pregnant women screened at the twenty-fourth to twenty-eighth week with a 50-g oral glucose challenge test followed by a universal 100-g oral glucose tolerance test. We used receiver-operator characteristic curve analysis, assembling positive and negative groups according to the different criteria adopted in oral glucose tolerance test interpretation (National Diabetes Data Group or Carpenter-Coustan) and in assignment of women with borderline glucose intolerance. Besides the statistical cutoff value, defined by the Youden index (Sensitivity + Specificity – 1), we also selected a “high-sensitivity” cutoff value, identified by the maximal sensitivity associated with >70% specificity. RESULTS: With use of National Diabetes Data Group criteria, the statistical and high-sensitivity cutoff values were set at 142 mg/dL when the positive group included only women with positive oral glucose tolerance test results and at 140 mg/dL when it also included subjects with borderline glucose intolerance. With use of Carpenter-Coustan criteria, the statistical cutoff value was set at 141 mg/dL when the positive group included only women with positive oral glucose tolerance test results and at 140 mg/dL when it also included subjects with borderline glucose intolerance; the high-sensitivity cutoff value was set at 140 mg/dL when the positive group included only women with positive oral glucose tolerance test results and at 136 mg/dL when it also included subjects with borderline glucose intolerance. CONCLUSIONS: We suggest maintaining the 140 mg/dL oral glucose challenge test threshold if the diagnostic target is to recognize only women with positive results of the oral glucose tolerance test. To prevent perinatal risks in pregnancies complicated by borderline glucose intolerance, with Carpenter-Coustan criteria a lower cutoff value (136 mg/dL) could be hypothesized to improve test sensitivity, allowing more extensive diagnosis of “borderline” subjects; however, the higher economic costs resulting from the increased false-positive rate and the limited improvement obtainable in sensitivity currently do not justify its generalized use. (Am J Obstet Gynecol 1998;179:179-85.)