Glucose challenge test

Definition

The glucose challenge test measures your body's response to sugar (glucose). The glucose challenge test is done during pregnancy to screen for gestational diabetes — a type of diabetes that develops only during pregnancy.

The glucose challenge test is done in two steps. First you drink a sugary solution. One hour later, your blood sugar level is measured. The results of the glucose challenge test indicate whether you might have gestational diabetes. If the test is positive, additional testing is needed to confirm the diagnosis.

The glucose challenge test is a modified version of the glucose tolerance test, a similar test used to screen for type 2 diabetes.

Why it's done

The glucose challenge test is used to screen for gestational diabetes. The test is often done between weeks 24 and 28 of pregnancy, although it can be done earlier if you're at high risk of gestational diabetes due to family history or other factors.

Most women who have gestational diabetes deliver healthy babies. However, without careful management, gestational diabetes can lead to various pregnancy complications, such as excess fetal growth — which may increase the risk of birth injuries or prompt a C-section delivery.

How you prepare

You can eat and drink normally 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 lab, you'll drink about 8 ounces (237 milliliters) of a syrupy glucose solution that contains 1.8 ounces (50 grams) of sugar. Often, the glucose solution is cola- or orange-flavored. One hour later, a member of your health care team will take a sample of blood by pricking your fingertip or inserting a needle into a vein in your arm. This blood sample will be used to measure your blood sugar level.

After drinking the glucose solution, you'll likely need to remain in the health care provider's office or lab while you're waiting for your blood sugar level to be tested. After the glucose challenge test, you can return to your usual activities immediately.

Results

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

One hour after drinking the glucose solution:

• A blood sugar level below 140 mg/dL (7.8 mmol/L) is usually considered normal
• A blood sugar level of 140 mg/dL (7.8 mmol/L) or higher may indicate gestational diabetes

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

If the results of your glucose challenge test indicate the possibility of gestational diabetes, your health care provider will do another blood test — typically the glucose tolerance test, which is done over the course of two to three hours — to confirm the diagnosis.