What is the screening test for gestational diabetes?
The oral glucose tolerance test (OGTT) is used to check for gestational diabetes. It measures the body's ability to use a type of sugar called glucose.
The test may be used in two different ways. Experts think that each method works as well as the other one.
The first method is done in two steps.
- A blood sample is taken after you drink a liquid that contains sugar (glucose). This may be called a glucose challenge test. You don't need to stop eating or drinking before this step. If you don't have a lot of sugar in your blood, you don't have gestational diabetes.
- If you have a lot of sugar in your blood, you will do the OGTT. With the OGTT, you cannot eat or drink for at least 8 hours before the test. If the test shows that you have a lot of sugar in your blood, you may have gestational diabetes.
Some experts do not use the two-step method. They just use another version of the OGTT. You cannot eat or drink for at least 8 hours before the test. Then:
- A blood sample is taken.
- You will drink a small cup of very sweet liquid.
- You will have follow-up blood tests after 1 to 3 hours. 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.
Why is an oral glucose tolerance test (OGTT) done?
An OGTT may be done to:
- Check for prediabetes and diabetes.
- Check for gestational diabetes during pregnancy.
How is an oral glucose tolerance test (OGTT) done?
- 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 that contains 75 or 100 grams of glucose.
- You will have more blood tests over 1 to 3 hours.
- Since activity can affect 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.
How do you prepare for an oral glucose tolerance test (OGTT)?
- Tell your doctor about all the prescription and nonprescription medicines you are taking. You may be told to stop taking certain medicines before the test.
- 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.)
What do the results of an oral glucose tolerance test (OGTT) mean?
Normal
Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.
High values
High glucose levels may be caused by:
- Diabetes.
- Gestational diabetes.
- Hyperthyroidism.
- Some medicines, such as corticosteroids, niacin, phenytoin (Dilantin), some diuretics, and some medicines used to treat high blood pressure, HIV, or AIDS.
- Large amounts of the hormone cortisol in the blood (Cushing's syndrome).
- Inherited diseases, such as hemochromatosis.
- Pheochromocytoma.
Low values
Low glucose levels may be caused by:
- Certain medicines, such as medicines used to treat diabetes, some blood pressure medicines (such as propranolol), and some medicines for depression (such as citalopram).
- Decreased production of the hormones cortisol and aldosterone (Addison's disease).
- Problems with the thyroid gland or an underactive pituitary gland.
- A tumor or other problems of the pancreas.
- Liver disease.
Many conditions can change blood glucose levels. Your doctor will discuss any significant abnormal results with you in relation to your symptoms and past health.
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