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Gestational diabetes screening

Screening tests for gestational diabetes (diabetes that occurs during pregnancy) assess the body's ability to manage glucose (a type of sugar) consumed in the diet.

There are two ways to screen for gestational diabetes. The preferred method is the sequential two-step approach. The first step is called the glucose challenge test. It involves taking a blood glucose test one hour after drinking a high-glucose solution (50 g of glucose). If the result is uncertain, an oral glucose tolerance test (OGTT) will be performed at a later date as the second step. The other screening method is a one-step process, involving only an oral glucose tolerance test (OGTT).

What is the purpose of this test? To screen for and diagnose gestational diabetes.
How to prepare?
  • For the glucose challenge (50 g of glucose): No need to fast.
  • For the OGTT (75 g of glucose): Fast. Do not eat or drink anything (except water) for at least 8 hours before your blood is drawn.
  • Follow the instructions you receive carefully.
Diagnostic values*

Blood glucose values 1 hour after ingestion of 50 g of glucose (glucose challenge test or first step of the sequential two-step process):

  • Normal: < 7.8="">
  • Unclear, clarify with OGTT (75 g of glucose): 7.8-11.0 mmol/L
  • Gestational diabetes: ≥ 11.1 mmol/L

An OGTT (75 g of glucose) can also be used to diagnose gestational diabetes. The diagnostic values for the OGTT (75 g of glucose) will differ if a glucose challenge test (50 g of glucose) was performed before the OGTT (75 g of glucose).

Associated tests Related tests include:
How is it done?

Glucose challenge test procedure:

  • You'll be given a few minutes to drink a liquid containing 50 g of glucose.
  • 1 hour after you drink the glucose solution, a blood sample will be drawn, usually from a vein in the arm.

OGTT procedure:**

  • At the beginning of the test, a blood sample will be drawn, usually from a vein in the arm.
  • You'll then be given a few minutes to drink a liquid containing 75 g of glucose.
  • Two more blood samples will be drawn 1 hour and 2 hours after you drink the glucose solution.

Precautions to be taken during testing:

  • Do not eat or drink anything (except water).
  • Stay seated; do not walk around.
  • Notify the medical staff if you experience dizziness, nausea, or vomiting.
How long before I get the results? Results are usually ready in a day. It may take longer to receive your results.
* These values are presented for information purposes only. As different laboratories may have different target values, the lab report usually specifies the values used for the test. It should also be noted that test results must be interpreted based on factors such as age and health condition. Values outside of this range may be considered normal for some individuals.
** Note that this test cannot be performed on the same day as the glucose challenge test.

What you should know before going for this test

When you go in for a blood test or any other medical exam, it's always a good idea to bring a complete list of any prescriptions, over-the-counter medications, or natural health products you're taking. Unless otherwise advised, it's best to take your medications as usual on blood test days. If in doubt, don't hesitate to talk to your healthcare professional.

© Copyright Vigilance Santé

The patient information leaflets are provided by Vigilance Santé Inc. This content is for information purposes only and does not in any manner whatsoever replace the opinion or advice of your health care professional. Always consult a health care professional before making a decision about your medication or treatment.

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