Your bodys reaction to sugar is measured by the glucose challenge test (GCT) often known as the one-hour glucose tolerance test (glucose). To check for gestational diabetes during pregnancy this test is carried out (diabetes that develops during pregnancy). If you are at high risk of gestational diabetes due to obesity a personal history of gestational diabetes and a family history of diabetes GCT can be performed as early as your first prenatal appointment. 140 mg/dL or greater blood sugar levels could be a sign of gestational diabetes.