The glucose challenge test, also called the one-hour glucose tolerance test, measures the body's response to sugar, called glucose. The glucose challenge test is done during pregnancy. The purpose of this test is to check for diabetes that develops during pregnancy. That condition is called gestational diabetes.

The test is done in two steps. The first is drinking a sugary drink. One hour later, blood sugar is measured. The results show whether gestational diabetes might be present.

If the test results fall outside the standard range, more testing may be needed to diagnose gestational diabetes.

Why it's done

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

People at average risk of gestational diabetes usually have this test done during the second trimester, generally between 24 and 28 weeks of pregnancy.

People at high risk of gestational diabetes might have this test done earlier than 24 to 28 weeks. Risk factors may include:

  • A body mass index of 30 or higher.
  • A lack of physical activity.
  • Gestational diabetes in an earlier pregnancy.
  • A medical condition linked to getting diabetes, such as metabolic syndrome or polycystic ovary syndrome.
  • Being 35 or older during pregnancy.
  • Diabetes in a blood relative.
  • Having had a baby in an earlier pregnancy who weighed more than 9 pounds (4.1 kilograms) at birth.
  • Being Black, Hispanic, American Indian or Asian American.

Most people who have gestational diabetes deliver healthy babies. However if it isn't carefully managed, gestational diabetes can lead to pregnancy problems. These can include a life-threatening condition called preeclampsia.

Gestational diabetes also can raise the risk of having a baby that's larger than usual. Having such a large baby might raise the risk of birth injuries or lead to a C-section delivery.

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

More Information

How you prepare

Before a glucose challenge test, you can eat and drink as usual. No special preparation is needed.

What you can expect

The glucose challenge test is done in two steps. When you get to where the test is being done, you drink a sweet syrup that has 1.8 ounces (50 grams) of sugar.

You need to stay in place while you wait for your blood sugar level to be tested. You can't eat or drink anything other than water at this point.

After an hour, a blood sample is taken from a vein in your arm. This blood sample is used to measure your blood sugar level.

After the glucose challenge test, you can return to your usual activities right away. You'll get the test results later.


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) signals the need for a three-hour glucose tolerance test to diagnose gestational diabetes.
  • A blood sugar level of 190 mg/dL (10.6 mmol/L) or higher indicates gestational diabetes. Anyone at this level needs to monitor blood sugar at home before breakfast and after meals.

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

People with gestational diabetes may be able to prevent complications by carefully managing blood sugar levels throughout the rest of the pregnancy.

The American College of Obstetricians and Gynecologists recommends that people diagnosed with gestational diabetes have a two-hour glucose tolerance test 4 to 12 weeks after childbirth to test for type 2 diabetes. If you have questions, talk to your obstetrician.

Sept. 08, 2023
  1. AskMayoExpert. Gestational diabetes mellitus. Mayo Clinic; 2022.
  2. Durnwald C. Gestational diabetes mellitus: Screening, diagnosis, and prevention. https://www.uptodate.com/contents/search. Accessed March 3, 2023.
  3. American College of Obstetricians and Gynecologists. Practice Bulletin No.190: Gestational diabetes mellitus. Obstetrics & Gynecology. 2018; doi:10.1097/AOG.0000000000002501.
  4. Tests & diagnosis for gestational diabetes. National Institute of Diabetes and Digestive and Kidney Diseases. https://www.niddk.nih.gov/health-information/diabetes/overview/what-is-diabetes/gestational/tests-diagnosis. Accessed March 9, 2023.

Glucose challenge test