Glucose Tolerance Testing (GTT) in Pregnancy

Pregnant woman getting her blood drawn
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Why the test is done:

This test is done to determine if you suffer from gestational diabetes or glucose intolerance of pregnancy.

How the test is done:

This test can be done fasting or non-fasting, with blood drawn from finger sticks or from your veins.

You may be asked to drink a special sugar enhanced drink called Glucola, eat jelly beans, or a specific breakfast, candy bar, etc. Your blood will then be tested for the level of glucose.

Which test you use will depend on the practice that you are in and the most recent research.

When the test is done:

It is usually offered to most women around 28 weeks gestation. However, if you have a family history of diabetes or had gestational diabetes in a previous pregnancy they may test you earlier. There are also places that say not everyone needs to be tested for gestational diabetes, though it is routine in many places. Given the risks associated with gestational diabetes, it is an important part of healthy pregnancy screening.

How the results are given:

A blood glucose of 139 and below is considered not gestational diabetic, anything above this reading will usually be sent for further testing. This further testing will be considered the definitive answer about a diagnosis of gestational diabetes.

Risks involved:

There are no risks involved in testing. This is a fairly non-invasive test requiring only blood from the mother.

Some women are concerned, rightfully, about the effects on a bolus of glucose to a baby who has not been used to receiving it is such quantities.

Alternatives:

Not testing or assuming you are glucose intolerant and beginning dietary precautions are the most common alternatives to testing.

Where do you go from here?

If you "fail" the one hour test you will be asked to take the three hour glucose test.

You will have your blood drawn fasting, then be asked to drink or eat something with sugar and will be tested at one hour, two hours, and three hours. You must pass in three of these tests to "pass" the entire test.

If you "fail" the three hour test you will more than likely be sent to a nutritionist to learn ways that you can control your glucose levels through diet. You will also have a plan for monitoring blood sugar levels to assess your progress. It is also important to note that if you are diagnosed with gestational diabetes, that you must also follow up after you have the baby with your primary care practice to talk to them about future screening for diabetes.

Sources:

Farrar D, Duley L, Medley N, Lawlor DA. Cochrane Database Syst Rev. 2015 Jan 21;1:CD007122. doi: 10.1002/14651858.CD007122.pub3. Different strategies for diagnosing gestational diabetes to improve maternal and infant health.

Garcia-Flores J, Cruceyra M, Cañamares M, Garicano A, Nieto O, Espada M, Lopez A, Tamarit I, Sainz De La Cuesta R. Gynecol Endocrinol. 2016 Feb 1:1-5. [Epub ahead of print] Weight-related and analytical maternal factors in gestational diabetes to predict birth weight and cord markers of diabetic fetopathy.

Wahlberg J, Ekman B, Nyström L, Hanson U, Persson B, Arnqvist HJ. Diabetes Res Clin Pract. 2016 Jan 12. pii: S0168-8227(16)00023-1. doi: 10.1016/j.diabres.2015.12.017. [Epub ahead of print] Gestational diabetes: Glycaemic predictors for fetal macrosomia and maternal risk of future diabetes.

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