This information leaflet has been produced by Gateshead Health NHS Foundation Trust Maternity Unit to provide information to pregnant people who are recommended to have an Oral Glucose Tolerance Test (OGTT).
What is an Oral Glucose Tolerance Test (OGTT)?
An OGTT is a test to see how your body handles a measured amount of sugar (glucose). In pregnancy it is usually performed between 24-28 weeks gestation, or shortly after your antenatal booking appointment if you have had gestational diabetes before. Occasionally it may need to be performed later (up to 32 weeks’ gestation), depending on clinical findings.
Gestational diabetes is a type of diabetes that arises specifically in pregnancy. It happens when your body cannot produce enough insulin (a hormone that controls your blood sugar levels), due to the hormonal changes that occur during pregnancy. As a result, your blood glucose levels will be higher than normal.
Why do I need to have the test?
Some women are at a higher risk of developing gestational diabetes than others.
You are at higher risk if you have any of the following risk factors:
- You have had gestational diabetes in a previous pregnancy.
- You have a body mass index (BMI) of 30kg/m2 or more.
- You have a history of bariatric surgery (*not all people are suitable for OGTT, see below).
- You have previously given birth to a large baby (over the 97th centile or weighing more than 4.5kg/9lb 9oz).
- You have a first degree relative with diabetes (Type 1 or 2).
- You are of an ethnic origin with a high prevalence of diabetes, including: African, South Asian (India, Pakistan, Bangladesh), Caribbean or Middle Eastern (Saudi Arabia, UAE, Iraq, Jordan, Syria, Oman, Qatar, Kuwait, Lebanon, Egypt).
- You have polycystic ovary syndrome (PCOS).
- If you are expecting more than one baby.
- If your midwife or care team have found glucose in your urine (a small amount on two occasions, or a larger amount on one occasion).
- If you have had a growth scan with excess liquor (water surrounding the baby).
- If you have had a growth scan where either the baby is measuring large for gestational age, or their abdominal circumference (tummy) is measuring larger than we would expect for their gestational age.
- If you are taking certain long-term medications, such as oral prednisolone or olanzapine.
- A previous stillbirth.
Usually, there are no symptoms to indicate that your blood sugar is high.
Who should not have the test?
*If you have had bariatric bypass surgery, the test will not be accurate and should not be offered. An alternative method of testing will be offered to you.
What do I need to do for the test?
Leading up to the test, please continue to eat your normal diet. On the evening before the test, do not have anything to eat or drink after 10pm (this includes chewing gum). You may drink small amounts of plain water to satisfy thirst.
On the morning of the test, do not eat any breakfast or drink anything other than sips of water.
You should also not smoke.
Please note that if you forget – and accidentally eat, drink or smoke – you must inform a member of staff on the morning of your test, as your appointment will need to be rearranged.
Pregnancy vitamins will not affect the results of your OGTT, but other medication may. Please inform your midwife prior to your test if you take any prescription or over-the-counter medications, and they will advise you on this.
You should wear something comfortable, such as a loose-sleeved top, so that your blood can be taken more easily.
We would also recommend bringing something to keep you occupied during your visit, and a light snack/drink to have once your test is completed.
What happens during the test?
- The test will take approximately 2.5 hours.
- The first blood sample (fasting) will be taken shortly after your arrival.
- You will then be given a drink containing glucose, which should be drunk within five minutes.
- You will be asked to stay with us for two hours. Please refrain from walking around, eating or smoking during this time, as it can affect the results of your test. Sips of water (only) are allowed.
- A second blood sample will be taken after 2 hours. After this, you can have something to eat/drink and leave.
Are there any side effects or risks?
There are no serious risks associated with having an OGTT.
Some people can become nauseated during the test, and occasionally vomit. If this happens the test will be abandoned, and you will be observed until you feel well enough to go home. Repeat testing, or an alternative test, will be offered.
There is a possibility of bruising around the site where the blood samples have been obtained, but this should heal without complication.
What if I choose not to have the test?
If you decide not to be tested for gestational diabetes, then it will not be possible to measure your blood sugar levels. If you have high blood sugar levels that remain undetected and untreated, the risks of gestational diabetes for both you and your baby are increased.
Your midwife or care team are very happy to discuss this in more detail with you.
When will I get the results of the test?
If either of your blood glucose samples (fasting or 2hr) are high, then this is means that you have gestational diabetes.
You will be contacted within three working days by a member of the joint Obstetric/Diabetes team and given an appointment to attend the Antenatal Clinic. Here, you will receive dietary advice, as well as information about how to monitor and manage your blood glucose levels and a plan for your antenatal care, to help keep you and your baby healthy.
If the blood glucose levels in both samples are normal, you do not have gestational diabetes, and your antenatal care will continue as planned. Your midwife will give you the results at your next routine appointment. The results will also be published on your Badger Notes app.
Useful sources of information
Please discuss any queries or concerns with your Community Midwife.
If you need additional information, please do not hesitate to contact the Diabetes Midwives.
Additional resources:
NHS – The NHS have written information available online.
Web: https://www.nhs.uk/conditions/gestational-diabetes/
Diabetes UK – Online resources and a support helpline available.
Web: www.diabetes.org.uk/diabetes-the-basics/gestational-diabetes
Tel: 0345 123 2399
At the Queen Elizabeth Hospital Maternity Unit, we advocate a shared decision making approach to all decisions made by our patients. This leaflet aims to give you additional information and to act as a point of reference following a discussion with your obstetrician or midwife. If you are asked to make a decision about your own care please make sure you have asked all the questions you need to ask and are given the appropriate time to do so. Some questions you might want to ask could be;
- What are my options?
- What are the pros and cons of each option?
- Who will support me making the decision that is the right one for me
Contact number
If you have any additional queries please contact:
If you need to cancel or re-arrange your appointment, please contact our appointments line between 8am – 6pm, Monday-Friday, so that we are able to offer this appointment to another patient.