A gestational diabetes test measures how your body handles sugar during pregnancy. This is usually done with an oral glucose tolerance test (OGTT) between week 24 and 28, in which your fasting blood sugar is drawn and drawn again after a sugar drink. The cut-off values determine whether gestational diabetes may be present.
I notice that the sugar test raises questions for many pregnant women: why do you have to come fasting, how much sugar is in that drink and what do those numbers mean? Below I walk calmly through the test. You will read what gestational diabetes is, when the OGTT is done and which blood values go with it.
What is gestational diabetes?
Gestational diabetes is a form of diabetes that develops during pregnancy and usually disappears again after birth. Your blood sugar becomes too high because the placenta makes hormones that counteract the action of insulin. According to the NVOG it occurs in a portion of pregnant women.
Normally your body keeps your blood sugar within a narrow range. In pregnancy your body needs more insulin, because placental hormones dampen insulin action. If your pancreas does not keep up with that extra demand, your blood sugar rises.
This usually happens only from the second trimester onwards.
Some women have a greater chance of gestational diabetes, for example with overweight, a relative with diabetes or a previous pregnancy with a high birth weight. Whether this applies to you is something you discuss with your midwife or GP. They decide together with you whether a sugar test is useful.
When is the sugar test (OGTT) done?
The sugar test is usually done between week 24 and 28 of pregnancy, the moment when gestational diabetes most often develops. With a raised risk your midwife may offer the test earlier, sometimes already in the first trimester. The exact moment depends on your situation and the guideline your care provider follows.
The timing is not random. From halfway through pregnancy the placenta makes more and more hormones, which raises the insulin demand. Around week 24 to 28 the effect of that is clearest to measure.
If you had gestational diabetes in a previous pregnancy, the test is often brought forward. With complaints or other risk factors your care provider may also draw blood earlier. The NVOG guideline Diabetes and pregnancy describes when testing is useful.
How does the glucose test work?
For an OGTT you come to the draw location fasting: you then have not eaten anything for at least eight hours. First your fasting blood sugar is drawn. Then you drink a glass with a fixed amount of dissolved glucose (usually 75 grams), and after one and two hours your blood is drawn again.
Between the draws you sit quietly, because exertion affects your blood sugar. Smoking and eating are not allowed during the test. This gives your care provider a clean picture of how your body processes the sugar.
The whole test takes about two to three hours.
Some women find the sugar drink a bit nauseating. That is unpleasant, but usually manageable. Let the staff member know if you do not feel well.
Which blood values go with gestational diabetes?
During the OGTT three glucose values are looked at: fasting, after one hour and after two hours. If one of these values is exceeded, gestational diabetes may be present. The table below shows commonly used Dutch cut-off values, but the exact thresholds can differ per lab and guideline.
| Measurement moment | Cut-off value (mmol/l) | What it measures |
|---|---|---|
| Fasting glucose | 5.3 or higher | Your blood sugar before the sugar drink |
| 1 hour after sugar drink | 10.0 or higher | The peak after taking the glucose |
| 2 hours after sugar drink | 8.4 or higher | How quickly your blood sugar falls again |
These values come from the NVOG guideline Diabetes and pregnancy and serve as guidance, not as a diagnosis. Some laboratories use slightly different thresholds or a different amount of glucose. Only your doctor or midwife can interpret the result in your situation.
Besides the OGTT your care provider sometimes looks at other values. A single fasting glucose gives a first impression, but is not enough for a diagnosis. The HbA1c value shows your average blood sugar over the past weeks and is used mainly outside pregnancy.
What does an abnormal result mean?
An abnormal result means that one or more glucose values are above the cut-off value. That is no reason to panic: gestational diabetes is usually treated well with adjusted nutrition, exercise and sometimes medication. Your midwife or gynaecologist discusses the next steps with you.
With gestational diabetes the focus is often first on lifestyle. Think of regular meals, fewer fast sugars and daily movement. If that does not get your blood sugar under control, insulin may be needed.
After birth gestational diabetes usually disappears on its own.
You do have a greater chance of developing type 2 diabetes later after a pregnancy with diabetes. So the NHG advises having your blood sugar checked occasionally in the years afterwards. You can find more explanation about the sugar test and the other draw moments in our overview on blood tests during pregnancy.
Testing your own blood sugar
The official sugar test runs through your midwife or GP, and that stays the place for the diagnosis. If you also want a picture of your blood sugar and related values yourself, for example before or between pregnancies, you can do so at Lunara without a referral.
At Lunara you order online, choose one of the more than 750 draw locations in the Netherlands and have blood drawn in the morning. You get your results digitally, each reviewed by a BIG-registered doctor. The Diabetes blood test looks at values like fasting glucose and HbA1c.
Important: testing yourself does not replace the sugar test or the regular pregnancy check-ups.
I mainly see testing yourself as a way to prepare the conversation with your care provider better. An abnormal value is not a diagnosis, but a reason to contact your GP or midwife. They look at the whole picture, not at a single number.
Frequently asked questions
Is the sugar test during pregnancy mandatory?
No, the test is voluntary. Your midwife usually offers it with a raised risk or with complaints. You decide together with your care provider whether the test is useful for you.
Do you have to be fasting for the glucose test?
Yes. For a reliable OGTT you eat nothing for at least eight hours beforehand. Drinking water is usually allowed. Follow the instructions you get from the draw location or your midwife.
Can you prevent gestational diabetes?
You cannot fully prevent it, but a healthy lifestyle with varied nutrition and enough exercise can help. The Voedingscentrum gives practical advice about eating during pregnancy. Discuss your personal risk with your midwife.
Does gestational diabetes disappear after birth?
Usually yes. In most women the blood sugar normalises after birth. The chance of type 2 diabetes later in life does stay raised, so an occasional check is sensible.
References
- NVOG. Guideline Diabetes mellitus and pregnancy. Dutch Society of Obstetrics and Gynaecology.
- NHG and Thuisarts.nl. Gestational diabetes. Dutch College of General Practitioners.
- World Health Organization (WHO). Diagnostic criteria and classification of hyperglycaemia first detected in pregnancy. WHO, 2013.
- Voedingscentrum. Nutrition during pregnancy.
Every blood test result through Lunara includes a professional assessment by a BIG-registered doctor. Blood testing through Lunara does not replace the regular pregnancy check-ups. For treatment decisions, discuss your results with your GP or midwife.
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