Oral glucose tolerance test (GTT) during pregnancy

Information for women, birthing people, and their families

This leaflet provides information on the oral glucose tolerance test (GTT) during pregnancy. If after reading this you have any questions or concerns, please speak to your midwife.

If you are unable to attend on the above date or time, please email your midwifery team as soon as possible so that they can rearrange.

What is an oral glucose tolerance test (GTT)?

A GTT is a test that checks if your body can use and store glucose (sugar).

Blood samples will be taken before and after a glucose (sugary) drink. The test checks the level of blood glucose (sugar) in your body. The drink will be very sweet and can sometimes make you feel a little nauseous (sick).

Why do I need a GTT?

You may have been advised to have a GTT if:

Who cannot have an oral GTT?

 You cannot have an oral GTT if you have had bariatric surgery (weight loss surgery). This includes:

Bariatric surgery changes the way that your body absorbs the nutrients that you eat.

An oral GTT puts you at increased risk of ‘dumping syndrome’. This is because an oral GTT requires you to drink glucose (sugar). Bariatric surgery causes this sugar to move from your stomach to your small bowel too quickly. This causes gastric dumping syndrome, and can make you unwell.

If you have had gastric / bariatric surgery, please tell your midwife. They will discuss the options available to you. As an alternative, you may be asked to monitor your blood sugar levels before and after a meal.

When will I have the test?

A GTT is usually carried out between 26 to 28 weeks of pregnancy. Your midwife will arrange this for you.

If you had gestational diabetes in a previous pregnancy, the GTT will be arranged for 16 weeks of pregnancy. If the 16 week test is negative, it will be repeated at 28 weeks.

What will the test tell me?

This test will help us to establish a diagnosis of gestational diabetes, which occurs only in pregnancy.

What is gestational diabetes? 

What causes gestational diabetes?

Hormones produced during pregnancy can make it difficult for your body to use insulin properly. So being pregnant puts you at an increased risk of insulin resistance.

Pregnancy places a heavy demand on your body. You may not be able to produce enough insulin to overcome this insulin resistance. This makes it difficult to use glucose (sugar) for energy. If glucose remains in the blood and the levels rise, this leads to gestational diabetes.

Gestational diabetes is common. It affects at least 4 to 5 in 100 women or birthing people during pregnancy.

What should I do before I come for my test?

You must fast for at least 8 hours, and not more than 14 hours before your test. This means that from the night before your test:

If you have medicine to take in the morning of your test still take this, unless told otherwise by your doctor. If your morning medicine needs to be taken with food, please speak with your midwife or doctor.

On the morning of your test, do not chew gum, vape, smoke or wear a nicotine patch. All of these will affect the results.

What will happen when I have the test?

Your fasting blood glucose level will be checked using a blood sample taken by pricking your finger.

If your finger prick test is below 7mmol

If your finger prick test level is above 7mmol

How will I feel after the test?

Further information

You can speak with your midwife or doctor if you have any more questions.

Useful contacts

If you have any further questions, please contact our Maternity telephone triage service on 01227 206737 for help and advice.

References