The findings in a recent blinded trial point to a definite graded relationship between fasting plasma glucose concentrations during oral glucose tolerance testing (OGTT) and a wide range of adverse obstetrical outcomes. This study examined whether measuring the fasting glucose concentration is a more convenient screening measure for gestational diabetes mellitus (GDM) than a 50-gm glucose challenge test. The prospective, population-based study enrolled 520 pregnant women who had a challenge test done at 24 to 28 weeks' gestation, followed within 1 week by a 3-hour, 100-gm OGTT after overnight fasting. The best cutoff values for fasting plasma glucose concentration were determined by analyzing receiver operating characteristic curves.
GDM was diagnosed in 10.2 percent of the participants, who tended to be older and more overweight than women with normal glucose tolerance. The optimal cutoff value of fasting plasma glucose was 4.8 mmol/liter, with a sensitivity of 81 percent and a specificity of 76 percent. Tolerance testing would be in order for the 30 percent of women who had criterion fasting glucose values. The best cutoff value for the glucose challenge test was 7.0 mmol/liter, which had a sensitivity of 68 percent and a specificity of 82 percent. Using the challenge test as a screening measure, 14 percent of women would require a diagnostic test.
These findings indicate that measuring the fasting plasma glucose concentration, using a cutoff value of 4.8 mmol/liter, is an easier means of screening for GDM than is the glucose challenge test. By measuring the fasting plasma glucose concentration, more than two-thirds of women can avoid a glucose challenge test. Although more OGTT will be necessary, this is more than made up for by avoiding so many challenge tests.
Br Med J 1999;319:812-815