- Those in the study group that test negative to the 1-hour GCT and 3-hour OGTT, and the participants in the control group will be followed routinely according to their medical and / or other obstetric conditions. At 24 - 28 weeks, they will undergo a 1-hour GCT and those that test positive will be also have the 3-hour OGTT based on current ACOG recommendation. If they are diagnosed with diabetes, they would receive the same standard-of-care interventions or treatments as necessary.