Appropriate time for 50 g oral glucose challenge test (50 g GCT) during pregnancy

Objective To evaluate the different effect of 50 g glucose challenge test (GCT) on screening the glucose intolerance at different gestational age. Methods Two thousand pregnant women were divided into 2 groups(1000 in each). Women in group A received 50 g GCT at 14 and 28 gestational weeks respectively and 75 g oral glucose tolerance test (OGTT) were performed in those cases with abnormal 50 g GCT. 50 g GCT was performed after fasting at 14 gestational weeks and repeated one hour after a meal at 28 gestational weeks. Women in group B were screened by 50 g GCT at 28 gestational weeks and followed by 75 g OGTT for those with abnormal 50 g GCT. The diagnostic effect of 50 g GCT for screening at different weeks of gestation with different ways was evaluated. Results (1)The rate of abnormal result of 50 g GCT was higher in fasting cases than that of cases testing after meal (15.6% vs 12.2%, P0.01). (2)50 g GCT at 14 weeks of gestation was of benefit to early diagnosis of glucose intolerance. (3)Repeated 50 g GCT at 24~28 weeks of gestation was necessary for screening the GDM (3.1%) and GIGT (2.0%) for those who had positive 50 g GCT at 14 weeks. (4)Repeated OGTT was necessary for uncontrolled GIGT cases in order to reclassification (4 cases from GIGT to GDM). Conclusions 50 g GCT at 14 weeks of gestation allows for an earlier detection for GDM. The false positive rate is lower in 50 g GCT performed 1 h after meal than that of fasting 50 g GCT. 50 g GCT at 24~28 weeks of gestation is necessary for a second screening. Early diagnosis of glucose intolerance can improve the maternal and fetal outcomes.