Patient Information

Pregnancy leaflets

Women’s Services
Colchester Hospital
Tel: 01206 742 483


Screening for diabetes in pregnancy


Diabetes that develops during pregnancy

This is known as gestational diabetes. It usually starts in the middle or towards the end of your pregnancy, rarely before 20 weeks of pregnancy. Certain characteristics can indicate that some women are more likely than others to develop gestational diabetes.

Your midwife or GP will check if:

  • you are overweight (body mass index or BMI 30kg/m² or higher)
  • you have given birth to a large baby before (weighing 4.5kg/10lbs or more)
  • you have a parent, brother or sister with diabetes
  • your family origin is South Asian, black Caribbean or Middle Eastern (these groups have a higher risk of developing gestational diabetes).

If any of the above apply to you, you should be offered the test for gestational diabetes. This test should be performed between 26 and 28 weeks of pregnancy.

If you have had gestational diabetes in a previous pregnancy, your midwife will arrange for you to have an additional test called an HbA1c at the same time as your booking blood tests. You will also be offered the test for gestational diabetes which is called an oral glucose tolerance test (sometimes shortened to OGTT or GTT). You may be asked to start monitoring your blood glucose levels using a meter. The GTT may need to be repeated at the normal time of 26–28 weeks of pregnancy if the first early test is normal.


Where can I have the test done?

This test is performed on an appointment basis; you can arrange this through the Antenatal clinic at Colchester Hospital or at the midwife-led units in Clacton and Harwich.


What does the test involve?

The test will take over two hours, so we suggest you bring something to occupy your waiting time. A fasting blood sample will be taken, and then you will be asked to drink a solution which contains glucose. A further sample will then be taken two hours later.


Risks associated with the test

No procedure is risk free. However, the GTT is usually associated with no more than nausea, occasionally vomiting and the discomfort (and possible bruising) caused by having two blood samples taken.



The day before your test, please eat your evening meal before 10pm. After this do not eat or drink anything other than plain water or black tea or coffee (without sugar or sweetener) until the test is finished. Do not drink fruit juices.

Continue with your prescribed medicine as normal.

Do not drink alcohol the evening before the test.

Do not smoke on the day of the test or chew gum. You will not be allowed to smoke or chew gum during the test because this may affect the results.

Colds or flu may cause abnormal results. If you are ill, please arrange another appointment.

We suggest that you sit and rest with minimal walking between each blood test as excessive activity may affect the results.


Contact details

If you have any further questions regarding this appointment please contact the unit where your test is to be performed.

Antenatal Clinic, Colchester Hospital 01206 742 483
Maternity Hotline, Colchester Hospital 01206 345 240
Clacton Midwife-led Unit 01255 201 600
Harwich Midwife-led Unit 01255 201 224


Further information

For more information on diabetes or the glucose tolerance test contact:

Diabetes midwife
Tel: 07586 472 140
Enquiries: 0345 241 3313 option 2
Email the diabetes midwife

NHS 111

Lab Tests Online website



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