Diabetes in pregnancy (gestational diabetes)

Gestational diabetes  is when you have high blood sugar (glucose) during pregnancy. This type of diabetes usually goes away after your baby is born.

You get gestational diabetes if your body cannot make enough insulin to meet your extra needs when you are pregnant. Insulin is a hormone (chemical substance) that helps to control the sugar levels in your blood. As a result, your blood sugar levels rise above normal.

Gestational diabetes can happen at any time when you are pregnant. However, it usually starts in the middle or towards the end of pregnancy.

This information explains:

The screening test is called an oral glucose tolerance test.

If the test shows that you have gestational diabetes, we will monitor your pregnancy and birth more closely. It is important to control your blood sugar levels to keep you and your baby healthy. This information explains how gestational diabetes can affect your pregnancy and how you can reduce complications.

If you have any other questions or concerns, please speak to your midwife, GP or diabetes team at the hospital.

Why an oral glucose tolerance test is important

We do an oral glucose tolerance test to check if you have diabetes during pregnancy (gestational diabetes).

It is important to know if you have gestational diabetes. This could result in your baby growing too big and cause problems when giving birth.

Gestational diabetes can have complications that affect you and your baby during pregnancy and after birth. But you can reduce the risks for you and your baby with the diabetes team's support. You can help to control your blood sugar levels during pregnancy by:

•    eating a healthy, balanced diet 
•    keeping active
•    taking diabetes medicines, if needed

If gestational diabetes is diagnosed early and well managed, this will help to keep you and your baby healthy.

Who needs an oral glucose tolerance test

You have been referred for an oral glucose tolerance test because 1 or more things (risk factors) make you more likely to get gestational diabetes. These could be:

  • a strong history of diabetes in close family members (for example, parents, brothers or sisters)
  • previously having gestational diabetes
  • previously having a large baby
  • when you keep getting sugar (glucose) in your urine (pee)
  • being overweight or obese (very overweight with a lot of body fat)
  • having too much fluid around your baby in the womb (polyhydramnios)
  • previously having shoulder dystocia (when the baby's shoulder gets stuck during birth)
  • previously having a baby who died during pregnancy or up to 1 year after birth
  • having a south Asian, Black, African-Caribbean or Middle Eastern family background (even if you were born in the UK)

Preparing for the test


  • bring your regular medicines and maternity book with you to the hospital
  • take a book, laptop or phone if you want to help pass the time while you are resting during the test


  • do not eat or drink anything (except water) from 10pm on the night before your test
  • do not take any medicines on the morning of the test

What happens during the test

An oral glucose tolerance test is made up of the following stages:

  1. We take a small sample of blood soon after you arrive.
  2. We give you a sugary (glucose) drink.
  3. We ask you to rest in the waiting area and avoid walking around as much as possible.
  4. We take a 2nd blood test 2 hours after your 1st blood test.

In total, you are in the hospital department for about 3 hours. After your 2nd blood test, you can:

  • immediately leave hospital
  • eat and drink
  • take any of your usual medicines

Risks of an oral glucose tolerance test

Some people feel sick (nausea) and cannot tolerate a sweet drink while they are pregnant. If you cannot manage to have all the sugary drink, we can book your oral glucose tolerance test for another date.

Getting your results

If the test shows that you do not have gestational diabetes, the results will be available at your next appointment with your midwife. We do not contact you especially.

If the test shows that you have gestational diabetes, we will contact you in 2 working days. We then make an appointment for you with the diabetes team.

We have more information about what being diagnosed with gestational diabetes means for you and your pregnancy.

Useful information and support


The NHS has information on gestational diabetes, and the screening and treatment for this condition.

Diabetes UK

Diabetes UK has information on gestational diabetes, and can give you guidance and support to manage this condition.

Phone: 0345 123 2399 (Monday to Friday, 9am to 6pm)
Email: [email protected]
Website: www.diabetes.org.uk

Royal College of Obstetricians and Gynaecologists

The Royal College of Obstetricians and Gynaecologists has information on:

  • what gestational diabetes is
  • how it is diagnosed
  • what extra antenatal care you can expect
  • what this diagnosis means for you and your baby, now and in the future

National Institute for Health and Care Excellence (NICE)

NICE has published an official guideline on managing diabetes in pregnancy. This guideline aims to improve the diagnosis of gestational diabetes. It is also intended to help people manage their blood sugar levels before and during pregnancy.

Resource number: 4381/VER3
Last reviewed: May 2023
Next review due: May 2026

A list of sources is available on request.

Trusted Information Creator. Patient Information Forum

Contact us

If you have any questions or concerns about the oral glucose tolerance test, please speak to your midwife. Their phone number is in your maternity notes. You can call from Monday to Friday, 9am to 5pm.

Out of hours, please leave a message and a member of staff will call you back in working hours. Otherwise, please contact your GP, go to 111.nhs.uk or call 111.

Pharmacy medicines helpline

If you have any questions or concerns about your medicines, please speak to the staff caring for you. You can also contact our pharmacy medicines helpline.

Phone: 020 7188 8748, Monday to Friday, 9am to 5pm

Email: [email protected]

We aim to respond to emails within 2 working days.

Do you have any comments or concerns about your care?

Contact our Patient Advice and Liaison Service (PALS)

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