What to Expect from a Glucose Tolerance Test: Gestational Diabetes Mellitus

What is a glucose tolerance test?

A glucose tolerance test, also known as an oral glucose tolerance test (OGTT), is a routine medical examination that measures how well the body handles sugar. The test measures the blood sugar level after you drink a sweet liquid called glucose. This liquid contains a high amount of sugar and is quickly absorbed by the body. After drinking the glucose, your blood sugar level will be checked every 30 minutes for 2 hours.


Why it’s done?

A glucose tolerance test is used to diagnose diabetes or prediabetes. Diabetes is a condition in which the body cannot properly use sugar for energy. Prediabetes is a condition in which the body has high blood sugar but is not high enough for a diagnosis of diabetes. A glucose tolerance test can also be used to check for gestational diabetes, which is diabetes that occurs during pregnancy.

If you have symptoms of diabetes, your doctor may recommend a glucose tolerance test.

The American College of Obstetricians and Gynecologists recommends screening for gestational diabetes in low-risk pregnant women between 24 and 28 weeks of pregnancy. If your doctor thinks you might be at risk or if the one-hour test showed a high value, you might need to take a three-hour glucose tolerance test.

How to prepare for a glucose tolerance test?

Your doctor will give you specific instructions on how to prepare for your glucose tolerance test.

  • You will need to fast (not eat or drink) for at least eight hours before the test.
  • You will also need to avoid strenuous activity for at least 24 hours before the test
  • Your doctor may also recommend that you stop taking certain medications before the test
  • Bring a list of all the medications you are currently taking, including supplements and vitamins
  • Bring your insurance card and driver’s license
  • Wear comfortable clothes that will allow the doctor to easily access your arm for the blood draw

If you have questions or concerns, be sure to ask the doctor ahead of time. Your doctor will schedule an appointment for you to have the test done. The test is usually done in the morning so that you can have breakfast afterward.

What happens during a glucose tolerance test?

When you arrive for your appointment, a nurse will take you to a room and have you sit or lie down.

  • Your blood sample is taken for fasting glucose.
  • You will then be given a glucose drink (100 gm) to consume.
  • The nurse will watch you for any side effects and take your blood sample to test your sugar level every 1 hour for the next 3 hours.
  • After the 3 hours are up, you will be able to eat and drink again.
  • You should expect to be at the appointment for a total of three to four hours.

What to expect after the glucose tolerance test?

After the test, you will be able to eat and drink as usual. You may experience some side effects from the test, such as dizziness, headache, or nausea. If you have any concerns, be sure to talk to your doctor.

Your doctor will go over the results of the test with you and explain what they mean. If your results are abnormal, your doctor may recommend additional testing or treatment.

Possible side effects of a glucose tolerance test

A glucose tolerance test is a common and safe medical test, but there are a few potential side effects to be aware of. You may experience the following side effects after drinking the glucose.

  • Dizziness
  • Headache
  • Nausea

What are some of the implications of having a high or low glucose tolerance level?

If your results are abnormal, it may be an indication of diabetes. If you have a high glucose tolerance level, it means that your body is not able to process sugar properly. This can lead to serious health complications, such as heart disease, stroke, and kidney disease.

If you have a low glucose tolerance level, it means that your body is able to process sugar properly.

However, this can still lead to health complications, such as weight gain, high blood pressure, and type II diabetes. It is important to talk to your doctor about your results so that you can develop a plan to manage your health.

What does the glucose tolerance test result reveal?

If your blood glucose level is higher than 140 mg/dL after the one-hour test, you’ll be diagnosed with gestational diabetes and your doctor will recommend the three-hour test.

Criteria for diagnosis of GDM with 100 gm oral glucose in three-hour test-

  • A normal fasting blood glucose level would be below 95 mg/dL or 5.3 mmol/L
  • After one hour from drinking the solution; the glucose level is 180 mg/dL or 10 mmol/L
  • At two hours, the glucose level is 155 mg /dL or 8.6 mmol/L
  • At three hours, the glucose level is below 140 mg/dL or 7.8 mmol/L

Gestational diabetes is diagnosed when any two values are met or elevated. You can prevent problems by carefully monitoring your blood glucose levels throughout the rest of your pregnancy if you’re diagnosed with gestational diabetes.

With proper treatment and lifestyle changes, most women with gestational diabetes will go on to have healthy pregnancies and babies.


The glucose tolerance test is a way to measure how well your body handles blood sugar. This test is done during pregnancy if you have gestational diabetes. Gestational diabetes can cause problems for both the mother and baby. To prepare for the test, you should not eat or drink anything except water for 8 hours before the test. The test is done by drinking a special sugary drink, then having blood drawn several times over the next few hours. The results of the glucose tolerance test will show how much sugar your body can handle over a certain period of time. If your results are abnormal, you may need to start treatment for gestational diabetes.

Leave a Reply

Up ↑