Objective

To determine the cut-off value for the 75-g glucose challenge test administered in early pregnancy to screen for gestational diabetes mellitus and abnormal carbohydrate metabolism in pregnancy.

Methods

A prospective study involving 1500 antenatal patients attending a community hospital. Patients were screened with the 75-g 1-h glucose challenge test in early pregnancy and subsequently tested with the 75-g 2-h glucose tolerance test to diagnose gestational diabetes mellitus. Statistical methods were employed to determine the optimal plasma glucose cut-off value for a positive result in early pregnancy.

Results

A glucose challenge test value of 6.0 mmol/L (108 mg/dl) or more was selected as the preferred cut-off level for further testing with a sensitivity of 83.5% (95% confidence interval [CI] 77.0%–88.9%) and specificity of 49.2% (95% CI 46.5%–52.0%).

Conclusion

An early pregnancy glucose challenge test reading of 6.0 mmol/L (108 mg/dl) or more is effective in screening for gestational diabetes mellitus; a value of 10.0 mmol/L (180 mg/dl) or more is effective for finding pre-pregnancy abnormalities of carbohydrate metabolism. The false-positive glucose challenge test diagnoses gestational hyperglycemia, the treatment of which will improve perinatal outcome. Further testing based on risk factors will exclude a false-negative glucose challenge test. A combination of universal early pregnancy screening and selective risk-factor testing is recommended to detect the full range of abnormalities of carbohydrate metabolism encountered in pregnancy.