Overview

The glucose challenge test, also called the one-hour glucose tolerance test, measures your body's response to sugar (glucose). The glucose challenge test is done during pregnancy to screen for gestational diabetes — diabetes that develops during pregnancy.

The test is done in two steps. First you drink a sugary solution. One hour later, your blood sugar level is measured. The results indicate whether you might have gestational diabetes.

If the test results are outside the standard range, you might need further testing to determine the diagnosis.

Why it's done

The glucose challenge test is used to screen for gestational diabetes during pregnancy.

If you're at average risk of gestational diabetes, you'll likely be screened during your second trimester — between 24 and 28 weeks of pregnancy.

If you're at high risk of gestational diabetes, your health care provider may recommend doing the screening as early as your first prenatal visit. Risk factors may include:

• Being or having a body mass index of 30 or higher (obesity).
• A lack of physical activity.
• Gestational diabetes in an earlier pregnancy.
• Having a medical condition associated with the development of diabetes, such as metabolic syndrome or polycystic ovary syndrome.
• Diabetes in a blood relative.
• Previously delivering a baby weighing more than 9 pounds (4.1 kilograms).
• Race and ethnicity — Women who are Black, Hispanic, American Indian and Asian American have a higher risk of developing gestational diabetes.

Most women who have gestational diabetes deliver healthy babies. However, without careful management, gestational diabetes can lead to pregnancy complications such as a serious condition that causes high blood pressure and other symptoms that can threaten the lives of both mother and baby (preeclampsia). Gestational diabetes can also increase your risk of having a baby with an excessive birth weight — which might increase the risk of birth injuries or prompt a C-section delivery.

Women who've had gestational diabetes also have a higher risk of getting type 2 diabetes.

How you prepare

You do not need to fast before the glucose challenge test.

What you can expect

The glucose challenge test is done in two steps. When you arrive at your health care provider's office or the lab, you'll drink a syrupy glucose solution that contains 1.8 ounces (50 grams) of sugar.

You'll need to remain in your health care provider's office or the lab while you wait for your blood sugar level to be tested. You can't eat or drink anything other than water at this point.

One hour later, a blood sample will be taken from a vein in your arm. This blood sample will be used to measure your blood sugar level.

After the glucose challenge test, you can return to your usual activities immediately. Your health care provider will give you the test results at a later time.

Results

Results of the glucose challenge test are given in milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L).

• A blood sugar level below 140 mg/dL (7.8 mmol/L) is considered standard.
• A blood sugar level of 140 mg/dL (7.8 mmol/L) to less than 190 mg/dL (10.6 mmol/L) indicates the need for a three-hour glucose tolerance test to diagnose gestational diabetes.
• A blood sugar level of 190 (10.6 mmol/L) or higher indicates gestational diabetes. Further testing might not be needed.

Some clinics or labs use a lower threshold of 130 mg/dL (7.2 mmol/L) when screening for gestational diabetes.

If you're diagnosed with gestational diabetes, you can prevent complications by carefully managing your blood glucose level throughout the rest of your pregnancy. The American College of Obstetricians and Gynecologists also recommends that women diagnosed with gestational diabetes have a two-hour glucose tolerance test 4 to 12 weeks after childbirth. This test screens for type 2 diabetes. If you have questions, talk to your health care provider.