Glucose Tolerance Test

A glucose tolerance test (GTT) or an oral glucose tolerance test (OGTT) is a screening test used to test your body to check how well it can regulate your sugar levels. It is offered to women at risk, usually between 26 and 28 weeks of your pregnancy, although may be offered earlier or later in pregnancy if needed.

The test can diagnose whether you have gestational diabetes which is a problem in pregnancy which affects between 2% and 4% of pregnant women.

The GTT is essential to diagnosing gestational diabetes as there are very few obvious signs of the problem and without the test, it could easily be undiagnosed and therefore untreated.

What is Gestational diabetes?
Your body makes insulin to regulate the sugar and glucose levels in your blood and it also allows your body to store any sugar that isn’t needed for use at a later stage. During pregnancy, especially as you approach the third trimester, your body will need to produce extra insulin as your baby also needs a supply as he grows.  Insulin is made in your pancreas, if your pancreas is unable to produce this extra insulin, it causes gestational diabetes. This is when the levels of sugar in your blood are too high.

Why might I be offered a GTT?
Your midwife will refer you for a GTT test if:

  • In a previous pregnancy, your baby was born large and weighing more than 4.5kg
  • There is a history of diabetes in your immediate family.
  • You are overweight and have a body mass index (BMI) of 30 or higher.
  • You have had gestational diabetes in a previous pregnancy.
  • You have been diagnosed with polycystic disease.
  • Your ethnic origin is Black Caribbean, South Asian or Middle Eastern.
  • When your urine was tested during your antenatal appointments, your glucose levels were either 1+ on two or more occasions or 2+ on a single occasion.

How is the GTT done?
Although it can depend on your location, a GTT is usually carried out in the maternity ward of your local hospital and usually during the morning. You are usually told to have a good meal, the evening before your test including a good portion of carbohydrates. You will then need to fast (not eat anything) until your test the following day. During this time you can drink water as necessary but you must not smoke or take any vitamin supplements, indigestion remedies or chew gum. Most essential prescribed medication can still be taken but you should inform your midwife which medication you are on prior to the test.

At the test, you will need to have a blood sample taken and then you are given a sugary drink known as Polycal and also a drink of water. You will be asked to drink both of these slowly over 5 minutes. You will need to drink all of both drinks. In some situations, you may be offered a high energy drink instead.

You will then be told to wait and after two hours, another blood sample will be taken. In some hospitals you may be allowed to go home or for a walk during this time. You are still not allowed to eat any food during this time. Both blood samples are then sent off for analysis to determine how your body copes with the sugar and whether you have gestational diabetes.

The results can take up to a week but many are returned within 48 hours. Your midwife will inform you how you can get your results.
If you have any concerns that you may have gestational diabetes or that you want more information on diabetes in pregnancy or on the glucose tolerance test, you should speak to your midwife.

by Jenny, mum to William and James

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