Glucose Tolerance Test

Get the facts

Gestational diabetes is the fastest growing type of diabetes in Australia, affecting thousands of pregnant women. According to Diabetes Australia, 12-14% of pregnant women will develop gestational diabetes and this usually occurs around the 24th to 28th week of pregnancy. A glucose tolerance test can be used to diagnose gestational diabetes. This is an important test for the health and safety of you and your baby.

What is the glucose tolerance test?

A glucose tolerance test measures how well your body is able to absorb glucose or sugar after you ingest a given amount of sugar. Doctors use a glucose tolerance test to diagnose the various types of diabetes, in particular, gestational diabetes. Doctors also use fasting blood sugar and haemoglobin A1c levels to evaluate diabetes. This is measured via a blood test.

What is gestational diabetes?

Gestational diabetes occurs when a pregnant woman who doesn’t have diabetes before pregnancy has high blood sugar levels as a result of the pregnancy. Undiagnosed gestational diabetes could harm you and your baby.

Who is at risk of gestational diabetes?

Gestational diabetes may occur in women with no known risk factors. Undiagnosed gestational diabetes may harm you and/or your baby. However, women who are at an increased risk of developing gestational diabetes include those who:

  • Are aged 40 years or over
  • Have a family history of type 2 diabetes or a first-degree relative (mother or sister) who has had gestational diabetes
  • Are above the healthy weight range
  • Have had elevated blood glucose levels in the past
  • Are from a Melanesian, Polynesian, Chinese, Southeast Asian, Middle Eastern, Indian, Aboriginal or Torres Strait Islander background
  • Have had gestational diabetes during previous pregnancies
  • Have previously had Polycystic Ovary Syndrome
  • Have previously given birth to a large baby (weighing more than 4.5kg)
  • Are taking some types of anti-psychotic or steroid medications
  • Have gained weight rapidly in the first half of pregnancy.

Is a glucose tolerance test harmful for your baby?

This is an important test for the health and safety of you and your baby.

When is the glucose tolerance test conducted?

All pregnant women should be tested for gestational diabetes at 24-28 weeks of pregnancy (except those women who already have diabetes). Women who have one or more of the risk factors are advised to have a diabetes test when their pregnancy is confirmed then again at 24 weeks if diabetes was not detected in early pregnancy.

What are the ingredients in the drink?

In Australia, the glucose tolerance test drink is manufactured by Point of Care Diagnostics (product code GTT75) and it will NOT harm you or your baby. The contents are filtered water containing 75g of glucose (Halal, Kosher, Gluten Free), food acid (330) and preservative (211, 202).

Before the test

In the lead up to the glucose tolerance test, you should:

  • Continue to eat a normal diet in the days leading up to the test.
  • Consult with your doctor about any medications you’re currently taking. Some medications, such as corticosteroids, beta-blockers, diuretics, and antidepressants, can interfere with the results.
  • Do not eat any food for at least eight hours before your test. You can drink water, but avoid other beverages including coffee and caffeinated tea as these can interfere with the results.
  • Consider bringing something to read or an activity to keep you busy while you wait as the test will take around two hours.

During the test  

  • When you arrive at your local NSW Health Pathology collection centre, a staff member will welcome you and outline the test procedure.
  • A staff member will then take a blood sample to measure your baseline glucose level.
  • You will then be asked to drink the glucose drink.
  • You will wait one hour in the collection centre and then a further blood sample will be taken from your arm.
  • After another one hour in the collection centre, another blood sample will be taken.
  • Food cannot be eaten during the period of the test as it will interfere with the results. It is ok to have small amounts of water.
  • Exercise must be kept to a minimum during the period of the test. As mentioned, we recommend you bring something to keep yourself rested and occupied.
  • Our staff will do their best to help keep you comfortable during the course of the test.

After the test

Your test results will be sent to your doctor who will discuss these with you. This will take approximately two business days.

For further information contact Dr Stephen Li, Chemical Pathologist p. 8890 7990 or Dr Joshua Ryan, Chemical Pathologist p. 8890 7990.

Download this fact sheet here.  (PDF 380.4KB)