The glucose challenge test measures your body's response to sugar (glucose). The glucose challenge test is done during pregnancy to screen for gestational diabetes; diabetes that develops during pregnancy.The glucose challenge test is done in two steps. First you drink a sugary solution. One hour later, your blood sugar level is measured. The results of the glucose challenge test indicate whether you might have gestational diabetes.If the test results are above normal, you'll need to have further testing to determine the diagnosis.