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3-Hour Glucose Tolerance Test

This test is done to evaluate how your body is processing sugar and to determine if you have developed Gestational Diabetes (Diabetes of Pregnancy).

The test requires a total of four blood draws. The first is done fasting (after you have had nothing to eat or drink for at least 8-12 hours prior—except water).

Then you will be given a glucose liquid to drink that has a specific amount of sugar in it. Blood samples will be taken one, two, and three hours after you have completed this drink.

In preparation for this test:

  • You should eat your normal diet prior to the day of testing.
  • Do not eat, drink, smoke, or exercise for at least 8-12 hours before your first blood sample is taken. You may drink plain water but no other beverages.
  • This test may take up to four hours to complete. Activity can interfere with the results so you will need to remain in the lab for the duration of the test.
  • Consider bringing something to read or a project to work on while waiting.
  • You may drink water so feel free to bring your own cup or water bottle.
  • Once the test is completed, you may resume normal eating and drinking. You may be hungry once the test is finished, so you may want to bring along a light snack to eat before leaving or driving home.

Gestational Diabetes is typically diagnosed when two or more of the results are elevated. Your doctor may also use other criteria to make the diagnosis.


Video Transcription:
Hi, I’m Nicole, I’m a nurse here at Moreland OB-GYN and I‘m here to you about our two glucose tests that we do during pregnancy. These tests measure the pregnant women’s reaction to glucose and screen for gestational diabetes which is a condition when a woman that does not have diabetes ends up with elevated high glucose levels. 
Having elevated blood sugar during pregnancy can affect your baby and your delivery. Advanced maternal age, your activity level, being overweight, or having a family member with diabetes all are factors that can contribute to gestational diabetes. First, I will explain the 1-hour glucose test, otherwise known as O’Sullivan Testing. You will be given a drink, like this, typically at your 24-week prenatal visit. You will be expected to drink the liquid prior to your next visit between 26 and 28 weeks of pregnancy. You need to drink this within 5 minutes, and then you will have to have your blood drawn one hour from that time. What does the drink taste like? It’s very sweet so we recommend drinking it straight from the fridge so it’s nice and cold to help control that sweetness. It is recommended to avoid foods or snacks that are high in sugar prior to the test. A normal or negative test result means you do not have gestational diabetes. However, an abnormal or positive test result means you are at risk for having gestational diabetes and we will need you to do the three-hour glucose test. So how does the three-hour test work? There are multiple blood draws for the three-hour glucose test, the first after fasting for 8-12 hours. Then you will be given a similar glucose liquid to drink and blood samples will be taken at 1, 2, and 3 hours after completing that drink. Because activity can interfere with the results, you will need to stay in the lab during the duration of the test, so we recommend bringing something to read, a project to work on, something to watch while you are waiting. You may drink plain water during the test however no food can be consumed at the time. Bring a snack for after cause you may be quite hungry. Based on the results of this test and other criteria that your doctor uses, you will be given a diagnosis. If you’re positive after this test, your physician will provide you information and other resources on how to manage your gestational diabetes. We hope this video gave you an overview of the testing performed to check for gestational diabetes. We have additional information on our website – Moreland o-b-g-n dot com, and if you still want more information, please ask your physician at your next visit. As always, it's our job here at Moreland to lead women to better health.

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