Objective: The objective of this study was to compare 2-hour postprandial glucose measurements with the standard 1-hour, 50 gm glucola screen as a predictor of gestational diabetes.
Study design: In this prospective study, 448 patients were screened for gestational diabetes mellitus after 20 weeks' gestation. Each patient was instructed to ingest a meal containing at least 100 gm of carbohydrate, and 2 hours later a plasma glucose level was obtained. Shortly after, each patient was given 50 gm glucola followed by a 1-hour glucose measurement. If either screen showed a result of 140 mg/dl or more, a formal 3-hour glucose tolerance test was done. Data were analyzed with use of the receiver operating characteristic curve.
Results: Of the 448 patients screened, 39 (8.7%) had a screening result of 140 mg/dl or greater and 16 (3.6%) of these had gestational diabetes mellitus. The receiver operating characteristic curve showed that the 1-hour glucose screen was more predictive of gestational diabetes than the postmeal assessment. The area under the receiver operating characteristic curve (plus or minus the SEM) for the 1-hour glucose test was 0.746 +/- 0.086 (p < 0.005) whereas the 2-hour postprandial test produced an area of 0.524 +/- 0.097 (p = NS). The range of optimal 1-hour glucola discriminatory values was 182 to 190 mg/dl. Thus the critical cutoff value of the 1-hour glucola test that minimizes false-positive results and maximizes true-positive screening for gestational diabetes is 182 mg/dl or greater.
Conclusions: The 1-hour glucola test is a reliable screening test for gestational diabetes mellitus whereas the 2-hour post-prandial test is not.