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Oral Glucose Tolerance Test During Pregnancy: About This Test

What is an oral glucose tolerance test (OGTT)?

An oral glucose tolerance test (OGTT) is one of several tests that check for gestational diabetes. You may have already had a different glucose screening test (for example, a glucose challenge test).

For the OGTT, you will prepare ahead of time by not eating before the test.

Gestational diabetes is a form of diabetes that can develop when you are pregnant. An OGTT measures your body's ability to use a type of sugar, called glucose, that is your body's main source of energy. If your blood sugar level first becomes too high when you are pregnant, you might have gestational diabetes. The condition usually goes away after the baby is born.

Why is this test done?

When you have gestational diabetes, a hormone called insulin is not able to keep your blood sugar in a normal range. This condition may not cause symptoms. That's why it's important for you to be tested for it. Most women are screened for gestational diabetes between the 24th and 28th weeks of pregnancy.

High blood sugar can cause problems for you and your baby. Your baby may grow too large, which can cause problems during delivery. Your baby may also be born with low blood sugar, which can cause seizures. But if you find out you have gestational diabetes, you can treat it with medicine and lifestyle changes. With treatment, most women are able to control their blood sugar and give birth to healthy babies.

How can you prepare for the test?

  • Tell your doctor about all prescription and non-prescription medicines you are taking. You may be told to stop taking certain medicines before the test.
  • For 3 days before the test, eat a balanced diet that contains carbohydrates.
  • Do not eat, drink, smoke, or do strenuous exercise for at least 8 hours before your first blood sample is taken. (You can drink water before the test.)
  • The test may take up to 3 hours, plus the time it takes for the doctor to see you. Since activity can interfere with test results, you will be asked to sit quietly during the entire test. Do not eat during the test. You may drink water during this time.

What happens during the test?

  • A blood sample is taken when you arrive for the test. This is your fasting blood glucose value. It will be compared to other glucose values in your blood.
  • You will drink a small cup of very sweet liquid.
  • Then you will have to wait for 1 to 3 hours for follow-up blood tests. How long you wait depends on the type of OGTT the doctor uses.
  • These follow-up blood tests measure how much sugar is in your blood. If you don't have a lot of sugar in your blood, you don't have gestational diabetes. If you do have a lot of sugar in your blood, you may have gestational diabetes.
  • The test might make you feel weak and hungry or sick to your stomach. Tell the person giving you the test if you have these symptoms.
  • There are many things that can change your blood sugar level. Your doctor will ask about your past health and discuss the results with you.

What happens after the test?

If you have gestational diabetes:

  • You may be able to control your blood sugar by changing the way you eat and exercising regularly.
  • You may have to check your blood sugar level at home and get follow-up glucose tests.
  • You may need to take medicine or give yourself insulin shots to help control your blood sugar.

Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor or nurse call line if you are having problems. It's also a good idea to keep a list of the medicines you take. Ask your doctor when you can expect to have your test results.

Where can you learn more?

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