Glucose Testing

Reviewed by Traci C. Johnson, MD on December 15, 2020

Who Gets the Test?

All women should get glucose testing during pregnancy. It's a standard test. It's especially important if you're having twins, because your risk of diabetes is higher.

What the Test Does

Glucose testing checks for a type of diabetes that can start when you're pregnant. Gestational diabetes is common and treatable. It usually goes away after birth. Without treatment, it can cause problems during pregnancy.

There are few basic tests. The glucose challenge screening tests how your body is processing blood sugar. If the results are abnormal, you will get a follow-up test. It's called a glucose tolerance test. If that's positive, you'll get treatment to get your glucose under control and keep your baby healthy.

Some women also get a blood test to check glucose called the A1C.

How the Test Is Done

Glucose tests are harmless to you and your baby. During the glucose challenge screening, you'll drink a small amount of glucose. After an hour, a nurse or phlebotomist will take a blood sample.

For the follow-up glucose tolerance test, you'll have to adjust your diet for a few days. Then you'll fast for 8 to 14 hours before the test. A nurse or phlebotomist will test your blood and then give you glucose. After that, they will take three more blood samples over the next few hours.

The A1C test is a simple blood test to check long-term glucose levels.

What to Know About Test Results

If you do have a positive result, try not to worry too much. Diabetes during pregnancy is common. As many as 1 in 10 pregnant women get it. Most have normal pregnancies and healthy babies.

Your doctor may recommend extra testing to check on your baby. You will need to keep your blood sugar under control with diet, exercise, and sometimes medicine.

Women who have gestational diabetes have an increased risk of developing diabetes later in life.

How Often the Test Is Done During Your Pregnancy

Women get glucose testing at 26 to 28 weeks.  Some women also get testing for glucose in early pregnancy if they have additional risk factors. If it turns out that you have diabetes, you'll get regular testing for the rest of your pregnancy. Your doctor may do an A1C blood test at your first prenatal check-up.

Other Names for This Test

Glucose challenge screening, glucose tolerance test, A1c test

Show Sources


American Diabetes Association: "What is Gestational Diabetes?"

Pagana KD, Pagana TJ. Mosby’s Diagnostic and Laboratory Test Reference, 10th ed., Mosby, 2010.

UptoDate: "Screening and diagnosis of diabetes mellitus during pregnancy."

Johns Hopkins Manual of Gynecology and Obstetrics, 4th Edition. Lippincott Williams & Williams, 2010.

James D. Goldberg MD, medical director, San Francisco Perinatal Associates, San Francisco.

U.S. Preventive Services Task Force (USPSTF).

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