Glucose Tolerance Test

Pregnant women can develop a condition known as Gestational Diabetes (diabetes brought on by pregnancy) which can pose a risk to both mother and baby. A glucose tolerance test is a common type of testing for potential gestational diabetes.

There are several tests intended to identify gestational diabetes in pregnant women. The first, called the Glucose Challenge Screening, is a preliminary screening test performed between 26-28 weeks. If a woman tests positive during this screening test, the second test, called the Glucose Tolerance Test, may be performed. This test will diagnose whether diabetes exists or not by indicating whether or not the body is using glucose (a type of sugar) effectively.
The Glucose Challenge Screening is now considered to be a standard test performed during the early part of the third trimester of pregnancy.

What is the Glucose Challenge Screening Test?

No preparation is required prior to the test. During the test, the mother is asked to drink a sweet liquid (glucose) and then will have blood drawn one hour from having the drink, as blood glucose levels normally peak within one hour. No fasting is required prior to this test.

The test evaluates how your body processes sugar. A high level in your blood may indicate your body is not processing sugar effectively (positive test). If the results of this screen are positive, the woman may have the Glucose Tolerance Test performed. It is important to note that not all women who test positive for the Glucose Challenge Screening test are found to have diabetes upon further diagnosis.

What is the Glucose Tolerance Test?

Prior to the taking the glucose tolerance test, your doctor will ask you to make sure and eat at least 150 mg of carbohydrates (about what you will get from a slice or two of bread) for three days prior to the time you will be asked to fast. You will not be permitted to eat or drink anything but sips of water for 14 hours prior to the test, so it is best to schedule the test for first thing in the morning.

Additionally, you should plan to have someone drive you to and from the test since your energy levels may be low and there is a slight possibility you may feel light-headed.

3-Hour Glucose Test

When you arrive, the technician will draw blood to measure your baseline “fasting blood glucose level”. You will be asked to drink a larger volume (or more concentrated solution) of the glucose drink than was used in the initial Glucose Challenge Screening test. Your blood will be drawn and tested every hour for the next three hours.

The following are the values that the American Diabetes Association considers to be abnormal during the Glucose Tolerance Test:

Interval Abnormal reading
Fasting 95 mg/dl or higher
One hour 180 mg/dl or higher
Two hours 155 mg/dl or higher
Three hours 140 mg/dl or higher

What if my Glucose Tolerance Test Results are Abnormal?

If only one of your readings comes back abnormal, your doctor may suggest some changes to your diet and/or test you again later in the pregnancy. If two or more of your readings come back abnormal, you’ll be diagnosed with Gestational Diabetes and your doctor or midwife will talk to you about a treatment plan. Treating diabetes during pregnancy is extremely important to protect the health of both mother and baby.

Want to Know More?

Compiled using information from the following sources:

1. American Diabetes Association

2. Emedicine

3. National Institute of Diabetes and Digestive and Kidney Diseases