Module 4
Screening for Gestational Diabetes
Gestational diabetes occurs in about 2–3% of pregnancies and usually develops after 24 weeks. We aim to detect it early, so that with nutrition guidance (and sometimes medication) we can stabilise your blood sugar levels, reducing risks for both you and your baby. The way to diagnose gestational diabetes is through an Oral Glucose Tolerance Test (OGTT). This test measures how your body handles glucose and whether pregnancy is affecting your blood sugar regulation. In this article we explain exactly who needs the test and how it works.
When do we recommend a glucose tolerance test?
Not everyone needs this test as part of routine care. We advise it when there is an increased risk of gestational diabetes, including if:
- You had diabetes in a previous pregnancy
- You are over 40 years old
- Your BMI was above 30 at your first visit
- You previously had a baby who weighed > P95 or > 4500 g
- A first-degree family member (parent, sibling) has diabetes
- You have an ethnic background with increased diabetes risk, such as South Asian (incl. Hindustani), African-Caribbean, Middle Eastern, Moroccan, or Egyptian
- You have ever lost a baby during pregnancy after 16 weeks
- You have Polycystic Ovary Syndrome (PCOS), diagnosed by a gynaecologist
- There are signs during pregnancy that may indicate diabetes, such as:
- a large estimated fetal weight
- excessive amniotic fluid
- you are very thirsty (> 3 litres per day)
If one or more of these points applies, we will recommend the glucose tolerance test.
Step‑by‑step: how the test works
- Make an appointment online at the OLVG laboratory.
Visit the OLVG website or click this link. Select: Glucose Tolerance Test (OGTT). We advise booking in the early morning as you must remain fasting until after the test. - Preparation at home
You must fast for 10 hours before the test: no food, no coffee or tea, no chewing gum. Only water is allowed. Scheduling the test early in the day helps. - Arrival at OLVG
Check in at the agreed time at the blood collection department. Bring your ID (passport, ID card, or driver’s licence). - The test itself
- First blood draw (T0): fasting, before eating or drinking anything.
- You drink a glucose drink within 5 minutes (a straw can help — bring one with you!).
- You then stay in the waiting area for 2 hours. Staying seated and relaxed is important — movement may affect the results.
- Second blood draw after 1 hour (T1).
- Third blood draw after 2 hours (T2). Then you are done.
- After the test
Bring a small snack to eat afterwards. If you feel well, you may go home and travel by bike, car or public transport.
Frequently asked questions about the OGTT
Why wait until 24 weeks to do the test?
Gestational diabetes only develops after 24 weeks of pregnancy. Testing earlier is not useful or reliable.
Why do I have to be fasting?
Because food and drink can affect your blood sugar levels. The test must measure your true fasting level — otherwise, the results won’t be accurate.
What are the normal values?
- T0 (fasting): less than 6.0 mmol/l
- T1 (after 1 hour): less than 12.0 mmol/l
- T2 (after 2 hours): less than 7.8 mmol/l
How will I receive the results?
If the result is abnormal, we will call you within a week. No phone call? That means the result is normal.
You can also check your results in your Mijn OLVG account.
Can I leave the hospital between the blood tests?
No. You must stay at the hospital and remain seated during the entire test. Movement can affect your blood sugar and alter the results.
What if I feel unwell after drinking the sugar solution?
That’s quite common — some people feel a little nauseous. Drinking through a straw can help. Bring a book, podcast, or music to distract yourself. Also bring a snack to eat afterwards and take your time before leaving.
What happens if my result is abnormal?
If one or more values are elevated, we’ll refer you to a dietitian. They will give you advice on healthy eating and drinking.
You will receive a blood sugar meter to use at home and check your levels several times a day. (We will explain how to use it!)
You write down your results and discuss them with the dietitian.
In 9 out of 10 cases, gestational diabetes can be managed well with a healthy diet — no medication needed.
If your blood sugar is stable, there is no longer an increased risk of complications.