Glucose challenge test (GCT) is commonly used in screening for gestational diabetes. No special preparation is needed for this test. Fifty grams of oral glucose is given between 24-28 weeks of gestation irrespective of the time or the meal and blood glucose is determined 1 hour later. A plasma value of 140 mg/dl is considered significant to perform the confirmatory diagnostic test. Ref: Essential of Obstetrics By Arulkumaran, 2004, Page 149 ; Dutta, 6th ed, Page 285