Most women are screened for gestational diabetes between the 24th and 28th week of pregnancy. Women who are considered at high risk (including women who have had gestational diabetes in a previous pregnancy) often are screened at an early prenatal visit. If test results are normal, they are screened again at 24 to 28 weeks.
The test involves drinking a liquid that contains 50 grams of glucose (a form of sugar). One hour later, the health care provider takes a blood sample. The sample is sent to the lab to measure the amount of glucose in the blood.
If the screening test shows that a woman has high levels of glucose in her blood, she needs to take a similar, though longer, test called the glucose tolerance test. It involves drawing blood samples while fasting and at 1, 2 and 3 hours after drinking 100 grams of glucose.
Most women diagnosed with gestational diabetes can control their blood-sugar levels with diet and exercise.