This test is performed routinely to determine whether you have gestational diabetes. Gestational diabetes is a form of diabetes that can develop in a pregnant woman who didn't have diabetes before pregnancy. It is caused by changes in a pregnant woman's metabolism and hormone production. The risk of gestational diabetes is higher in women over 30, who have a family history of diabetes, or who are obese.
A glucose tolerance test is usually done between the 24th and 28th weeks of pregnancy. You will be asked to drink a glucose solution and after an hour, blood is drawn and the glucose level is checked. About 15 percent of pregnant women who are given a glucose tolerance test will have abnormal levels and a second test is done.