Objective

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

Methods

A prospective study involving 1,500 antenatal patients attending a community hospital. Patients were screened with the 75-gram 1-hour glucose challenge test in early pregnancy and subsequently tested with the 75-gram 2-hour 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

The glucose challenge test ≥6.0mmol/L (108mg/dL) was selected as the preferred cut-off level for further testing with a sensitivity of 83.5% (95% CI 77.0-88.9) and specificity of 49.2% (95% CI 46.5-52.0).

Conclusion

The early pregnancy glucose challenge test ≥6.0mmol/L (108mg/dL) is effective in screening for gestational diabetes mellitus and when ≥10.0mmol/L (180mg/dL) for pre-pregnancy abnormalities of carbohydrate metabolism. The false-positive glucose challenge test diagnoses gestational hyperglycaemia 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.