Objective: This study was undertaken to determine use of different cut-off values with regard to the time of the patient's last meal in screening for gestational diabetes mellitus which could result in better results and change patient management. Methods:: Two hundred and seventy-four non-diabetic women undergoing routine screening for glucose intolerance between 26 to 28 weeks' gestation were classified with regard to the time of previous meal. A glucose challenge test and an oral glucose challenge test were conducted for each patient in the study. Results were evaluated with both a standard cut-off value of 140 mg/dl without regard to the time of the last meal and suggested cut-off values of 148 mg/dl, 142 mg/dl, and 150 mg/dl if the patient ate < 2 h, 2-3 h, and > 3 h before the screening test, respectively. Results: Two hundred and seventy-four women completed the study. With these suggested cut-off values, the number of patients with a positive glucose challenge test dropped from 15.7% to 11.3%. With these cut-off values, positive predictive value increased from 27.3% to 32.3%. Conclusions: The time since previous meal affects 50 g glucose challenge test results. These new cut-off values would lead to improved efficiency of the screening test and decreased frequency with which patients require the 3-h oral glucose tolerance test. (C) 1997 International Federation of Gynecology and Obstetrics.