This page is intended for all pregnant women who have been asked to attend for an oral Glucose Tolerance Test (GTT).

What is a GTT?

This test is a way of examining how your body handles glucose. The GTT can detect a type of diabetes which occurs only in pregnancy, called gestational diabetes. For more information about gestational diabetes, please visit the website provided at the end of this page.

The GTT test will involve having 2 blood tests and drinking a measured amount of glucose (sugar drink).

Why do I need an oral GTT?

There are several reasons for recommending an oral GTT test in pregnancy, these include:

  • A first-degree relative (parent, sibling or child) with diabetes.
  • Family origins of Afro-Caribbean, South-east Asian or Middle Eastern.
  • A diagnosis of Polycystic Ovarian Syndrome (PCOS).
  • A Body Mass Index (BMI) of 30 or above.
  • Delivering a previous baby weighing more than 4.5kg.
  • A previous stillbirth.
  • If your ultrasound measurements shows that you are having a large baby.
  • If your ultrasound scan shows excess liquor (water surrounding the baby).

Before the test

  • You should eat normally for at least 3 days.
  • Do not eat any food after 10:00 pm on the evening before the test. You are allowed to drink water but avoid all other drinks.
  • Do not chew gum/sugar free sweets, or use e-cigarettes or nicotine patches.
  • Other than water, do not have anything to eat or drink on the morning of the test.

During the test

A blood sample will be taken from your arm before you are given a glucose drink called Polycal®.

Polycal® is a flavoured drink containing the equivalent of 75g of glucose and must be drunk within 5 minutes.

Following the Polycal® drink you will be asked to drink 100mls of water. You may continue to drink water throughout the remainder of the test.

A second blood sample will be taken 2 hours after finishing the Polycal® drink. Both blood samples will be sent to the laboratory for glucose analysis. If you feel unwell at any point during the test, please inform a member of staff. You must sit quietly and not smoke, chew gum or sweets during the 2 hours of the test.


The results are normally available the following working day.

You will be informed by telephone only if your results are not within the normal ranges, and will be given an appointment with the diabetes nurse to discuss this further.

Cancelling your appointment

If you cannot attend for the GTT for any reason then please contact the appropriate Antenatal Clinic using the numbers at the end of this page.

Points to remember

Have nothing to eat or drink other than water, after 10:00 pm the evening before the test.

You may want to bring something to read as you will be expected to rest while waiting for the second blood sample to be taken. It is also advisable to bring some food and drink for after the test.

As you will be in the department for up to 3 hours, please bear this in mind when parking if you are travelling to the hospital by car. If your test is at Gloucestershire Royal Hospital, we recommend that you park in the tower car park which operates a pay on leaving system.


A member of the healthcare team with arrange an appointment for your oral Glucose Tolerance Test (GTT). Your appointment will be at one of the following locations:

  • Maternity Assessment, The Women’s Centre, Gloucestershire Royal Hospital
  • Maternity Assessment Centre, St. Paul’s Wing, Cheltenham General Hospital
  • Stroud General Hospital

Contact information

Maternity Assessment

The Women’s Centre

Gloucestershire Royal Hospital

Tel: 0300 422 6104

Monday to Friday, 8:30am to 4:30pm

Maternity Assessment Centre

Cheltenham General Hospital

Tel: 0300 422 4373

Monday to Friday, 8:30am to 12:30pm

Antenatal Clinic

Cheltenham General Hospital

Tel: 0300 422 2347

Monday to Friday, 8.30am to 4.30pm

Stroud Maternity

Tel: 0300 421 8018

Further information

For more information about gestational diabetes please visit:



If you would like to learn more about the oral Glucose Tolerance Test (GTT), please visit the ‘Lab Tests Online’ website. This is a free resource created and updated by laboratory professionals for patients.

Lab Tests Online


Printable version of this page

Oral Glucose Tolerance Test (GTT) in pregnancy GHPI1375_06_23 Department: Maternity Review due: June 2026 PDF, 322.3 KB, 5 pages
Reference number GHPI1375_06_23
Department Maternity
Review due June 2026