This is a medical question of type : exams and tests 
 How to diagnose Diagnosis of Diabetes and Prediabetes ? 
 Health care providers test for gestational diabetes using the OGTT. Women may be tested during their first visit to the health care provider after becoming pregnant or between 24 to 28 weeks of pregnancy depending on their risk factors and symptoms. Women found to have diabetes at the first visit to the health care provider after becoming pregnant may be diagnosed with type 2 diabetes.
                
Defining Safe Blood Glucose Levels for Pregnancy
                
Many studies have shown that gestational diabetes can cause complications for the mother and baby. An international, multicenter study, the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study, showed that the higher a pregnant womans blood glucose is, the higher her risk of pregnancy complications. The HAPO researchers found that pregnancy complications can occur at blood glucose levels that were once considered to be normal.
                
Based on the results of the HAPO study, new guidelines for diagnosis of gestational diabetes were recommended by the International Association of the Diabetes and Pregnancy Study Groups in 2011. So far, the new guidelines have been adopted by the American Diabetes Association (ADA)3 but not by the American College of Obstetricians and Gynecologists (ACOG)4 or other medical organizations. Researchers estimate these new guidelines, if widely adopted, will increase the proportion of pregnant women diagnosed with gestational diabetes to nearly 18 percent.5
                
Both ADA and ACOG guidelines for using the OGTT in diagnosing gestational diabetes are shown in the following tables.
                
Recommendations for Testing Pregnant Women for Diabetes
                
Time of testing    ACOG    ADA        At first visit during pregnancy    No recommendation    Test women with risk factors for diabetes using standard testing for diagnosis of type 2 diabetes.  Women found to have diabetes at this time should be diagnosed with type 2 diabetes, not gestational diabetes.        At 24 to 28 weeks of pregnancy    Test women for diabetes based on their history, risk factors, or a 50-gram, 1-hour, nonfasting, glucose challenge testa modified OGTT.  If score is 130140 mg/dL, test again with fasting, 100-gram, 3-hour OGTT.*    Test all women for diabetes who are not already diagnosed, using a fasting, 75-gram, 2-hour OGTT.*
                

                
OGTT Levels for Diagnosis of Gestational Diabetes
                
Time of Sample Collection    ACOG Levels**,4 (mg/dL)    ADA Levels3(mg/dL)        100-gram Glucose Drink    75-gram Glucose Drink        Fasting, before drinking glucose    95 or above    92 or above        1 hour after drinking glucose    180 or above    180 or above        2 hours after drinking glucose    155 or above    153 or above        3 hours after drinking glucose    140 or above    Not used        Requirements for Diagnosis    TWO or more of the above levels must be met    ONE or more of the above levels must be met
                

                

                

                
More information about treating gestational diabetes is provided in the NIDDK health topic, What I need to know about Gestational Diabetes, or by calling 18008608747.