IMPACT OF TIME SINCE LAST MEAL ON THE GESTATIONAL GLUCOSE CHALLENGE TEST

OBJECTIVE: The purpose of the study was to evaluate the impact of time since the last meal on the glucose challenge test and to find cut poi nts that are most likely to predict the outcome of the oral glucose to lerance test in patients screened for gestational diabetes. STUDY DESI GN: This prospective analytic cohort study was carried out at the Univ ersity of Toronto Perinatal Complex. A 50 gm glucose load was given at 26 weeks' gestation and the time since previous meal ingestion was re corded. At 28 weeks' gestation a 100 gm oral glucose tolerance test wa s administered. A total of 4274 eligible patients were screened. RESUL TS: Time since the last meal had a marked effect on mean plasma glucos e. Receiver-operator characteristic curve analysis with National Diabe tes Data Group criteria to interpret the oral glucose tolerance allowe d the selection of the most efficient cut points for the glucose chall enge test on the basis of time since the last meal. These cut points w ere 8.2, 7.9, and 8.3 mmol/L for elapsed postprandial times of <2, 2 t o 3, and >3 hours, respectively. With this change from the current thr eshold of 7.8 mmol/L the number of patients with a positive screening test dropped from 18.5% to 13.7%. There was an increase in positive pr edictive value from 14.4% to 18.7%. The rate of patient misclassificat ion fell from 18.0% to 13.1%. CONCLUSION: We suggest that screening st rategies for detection of gestational diabetes be reconsidered, to acc ount for the impact of variable postprandial status on the test result s.