Yes. Classic risk factors (obesity, family history of diabetes, etc.) only identify about 50% of women with the disease. The best time to screen is between 24 and 28 weeks, when the test has a sensitivity of 75%. If the test is delayed, the chance to prevent fetal macrosomia would be missed. The test should be repeated in the third trimester if glycosuria is found, toxemia or hydramnios develop, if the fetus is large for the gestation dates, or if the mother is obese (more than 120% ideal weight).