Twenty-six studies based on 25 articles (13,564 women, range 42 to 3,836; included 1,027 with gestational diabetes mellitus) were included in the review. There was one randomised controlled trial, one cross-sectional study and 24 cohort studies. The reference test was performed independently and consistently in all studies. Most studies did not blind interpreters of the oral glucose tolerance test from the results of the glucose challenge test. Most studies did not perform correction for verification. Twenty studies had consecutive (unselected) recruitment and four recruited a high risk population. Four studies reported inclusion based on the presence of risk factors; one study did not report methods used. Withdrawals were explained in approximately 70% of the included studies.
Low threshold oral glucose tolerance test: Based on a threshold value of 7.8mmol/L and low threshold oral glucose tolerance test, the 50g glucose challenge test had a pooled sensitivity of 74% (95% CI 62 to 87), specificity of 85% (95% CI 80 to 90), positive likelihood ratio of 4.9 (95% CI 3.5 to 7.0) and negative likelihood ratio of 0.31 (95% CI 0.20 to 0.47) for studies with an unselected population. For studies with a high risk population sensitivity was 74% (95% CI 62 to 87), specificity was 77% (95% CI 66 to 89), positive likelihood ratio was 3.2 (95% CI 2.0 to 5.2) and negative likelihood ratio was 0.34 (95% CI 0.22 to 0.53).
High threshold oral glucose tolerance test: Based on a threshold value of 7.8mmol/L and high threshold oral glucose tolerance test, the 50g glucose challenge test had a pooled sensitivity of 83% (95% CI 75 to 91), specificity of 81% (95% CI 75 to 87), positive likelihood ratio of 4.4 (95% CI 3.2 to 6.0) and negative likelihood ratio of 0.21 (95% CI 0.14 to 0.32) for studies with an unselected population. For studies with a high risk population sensitivity was 83% (95% CI 75 to 91), specificity was 72% (95% CI 60 to 84), positive likelihood ratio was 3.0 (95% CI 2.0 to 4.5) and negative likelihood ratio was 0.24 (95% CI 0.15 to 0.37).
The only covariate to impact on results was threshold of the 50g glucose test which was statistically significant for both sensitivity and specificity. Results for 7.5 and 8.0 thresholds and summary ROC curves were reported.