Glucose Tolerance Test (GTT)

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Extra Tests You May Be Offered

A Glucose tolerance test (GTT) is a way of examining how your body handles glucose. If a GTT is deemed necessary it is routinely performed at 26-28 weeks of pregnancy (earlier if you have had gestational diabetes previously). You should ring your GP surgery who will be able to organise an appointment for the test.

If the result is not as expected you will be referred to Southmead Hospital Antenatal Clinic Diabetes Obstetric Team.

Why do I need a GTT?

During pregnancy some women develop gestational diabetes, which usually resolves after your baby is born, and a further blood test with your GP surgery will be taken six weeks after delivery to ensure this. It is important that this is recognised in order for the appropriate advice and treatment to be accessed, for the wellbeing of you and your baby.

Some people are more likely to develop gestational diabetes if they have:

  • A family history of diabetes
  • A body mass index of greater than 30
  • Delivered a larger than average weight baby
  • Had gestational diabetes in a previous pregnancy
  • Have a family origin with a higher prevalence to diabetes, such as being of South Asian, Afro-Caribbean or Middle Eastern decent.

What should I do before coming for the GTT?

You should eat normally for at least three days before the test and not restrict your food intake.

On the evening before the test, stop eating any food by 10pm. You are allowed to drink water but avoid all other drinks such as tea, coffee, chocolate drinks, fruit juices, squashes, lemonades and alcohol.

Other than water, do not have anything to eat or drink on the morning of the test.
Check with your GP that you can delay taking any medication on the morning of the test until after it is finished.

During the test

You will have a small blood sample taken from your arm before you are given a measured amount of the glucose to drink, equivalent to 75g of glucose.
Two hours after finishing the drink the second blood sample will be taken from your arm. During the two hours you must sit quietly at the surgery and not smoke. Using any energy, even minimal, will invalidate the test and it will have to be repeated.

Samples are sent to the laboratory for glucose analysis. You can call your midwife for the results on the 5th day after the test is taken.

For more information visit

Diabetes in pregnancy: Management of diabetes and its complications from pre-conception to the postnatal period, NICE (2008).