Abnormal results on a second testing and risk of gestational diabetes in women with normal baseline glucose levels

To examine the rate of women with normal initial results to glucose tolerance tests who have abnormal results to subsequent testing, and estimate the risk of gestational diabetes mellitus (GDM) in these women.

Baseline plasma glucose levels were classified as normal if they were less than 120 mg/dL (group 1) or between 120 and 139 mg/dL (group 2) by the 50-g glucose challenge test (GCT); as abnormal if they were found abnormal by the 50-g GCT but normal by the 100-g glucose tolerance test (OGTT) (group 3); and as abnormal if 1 of the four 100-g OGTT values was abnormal (group 4). A second testing session with the 50-g GCT and 100-g OGTT was performed between the 24th and 28th weeks of pregnancy for 900 women at risk whose initial test results were normal.

Of the 823 women with normal baseline results who completed the study, 41.4% had abnormal results to the second 50-g GCT, and gestational diabetes mellitus was diagnosed by the 100-g OGTT in 7.0% of these 823 women. Compared with group 1, the women in groups 2, 3, and 4 were at a significantly increased risk of having an abnormal result to the second 50-g GCT. They were also at a significantly increased risk for GDM. The adjusted odds ratios (ORs) were 3.0 for group 2 (95% confidence interval [CI], 1.2-7.2), 4.9 for group 3 (95% CI, 2.2-11.0), and 11.3 for group 4 (95% CI, 3.9-32.6).

The risk of developing GDM significantly increased with increasing baseline plasma glucose levels by the 50-g GCT.