The glucose tolerance test screens for gestational diabetes during pregnancy. Typically, your doctor or medical professional will ask you to have a glucose screening test first. Depending on the results from the glucose screening test, you might then need to have a glucose tolerance test as well.

The glucose screening test measures your blood sugar at the time of your test. You’ll have a drink that contains glucose, and 1 hour later, a healthcare professional will draw blood to check your blood sugar levels.

A normal test result is typically 140 milligrams per deciliter (mg/dL) or lower. If your test result is higher than that, your doctor will ask you to have a glucose tolerance test.

You’ll need to fast overnight before your glucose tolerance test. To perform the test, a healthcare professional will first draw a sample of blood to check your fasting blood sugar levels.

You’ll then have a drink that contains glucose. The healthcare professional will draw another blood sample 1, 2, or possibly 3 hours later, depending on the test provider, to check your blood sugar levels again.

The following ranges show what your glucose tolerance test results mean:

  • Normal: 140 mg/dL or lower
  • Prediabetes: 140 to 199 mg/dL
  • Diabetes: 200 mg/dL or higher

A test result of 200 mg/dL or higher 2 hours after having your glucose drink might mean you have gestational diabetes. Your doctor may sometimes want to repeat the test before making a diagnosis of gestational diabetes.

For more information about how to prepare for your glucose tolerance test, check out: “Gestational Diabetes Test: What to Expect.”