During your pregnancy, your doctor will schedule you for the oral glucose tolerance test (OGTT), usually done between 24 and 28 weeks of pregnancy.
Here is what to expect from the OGTT glucose test in pregnancy, including how to prepare, who may need earlier screening, how Singapore’s glucose thresholds work, and what happens if you are diagnosed with gestational diabetes.
What is the OGTT in pregnancy?
The oral glucose tolerance test (OGTT) checks how your body processes glucose, or sugar, during pregnancy. It is used to screen for gestational diabetes mellitus (GDM), which can develop during pregnancy even if you have not had diabetes before [1] [2].
In Singapore, the standard OGTT is usually done between 24 and 28 weeks of pregnancy. It is a three-point test that takes around two to three hours to complete [2].
The test typically involves:
- Having a fasting blood sample taken when you arrive
- Drinking a glucose solution containing 75g of sugar within about five minutes
- Having another blood sample taken one hour after the drink
- Having a final blood sample taken two hours after the drink
During the waiting period, you will generally need to remain seated and avoid eating or drinking anything other than water. Bring a book, headphones, downloaded show or something else to keep you occupied.
How to prepare for your OGTT
The most important part of OGTT glucose test preparation is fasting beforehand. Your healthcare provider will give you specific instructions, but you will generally need to fast overnight before the test. Some Singapore hospitals advise fasting from midnight, while other guidance specifies at least eight to 10 hours of fasting [3].
During your fast:
• Do not eat
• Drink only plain water unless your healthcare provider tells you otherwise
• Avoid strenuous exercise before the test
• Take any medications or supplements only according to your doctor’s instructions.
You do not need to deliberately cut out sugar or carbohydrates for several days beforehand. Continue eating and exercising normally before the test unless your healthcare team gives you different instructions. The aim is to assess how your body responds to glucose under standard test conditions.
Supermom tip: If you can choose your appointment time, an early morning slot can make the fasting period easier to manage. Pack a snack for after your final blood draw, as you may be hungry or light-headed by then.
Wear comfortable clothing with sleeves that can be rolled up easily. You will have multiple blood draws, so easy access to your arm can make the appointment more comfortable.
Who may need an OGTT earlier?
Although most pregnant women are screened at 24 to 28 weeks, your doctor may recommend earlier gestational diabetes screening if you have certain risk factors.
These can include [2] [3]:
• A BMI above 25kg/m²
• A previous baby weighing more than 4kg
• A previous history of gestational diabetes
• Prediabetes
• A family history of diabetes
• Being aged 40 or above
What do the OGTT results mean?
One of the most useful things to know before your appointment is that there are specific blood glucose thresholds used to diagnose gestational diabetes in Singapore.
For the three-point OGTT, the thresholds are:
| Test | Gestational diabetes threshold |
| Fasting | ≥ 5.1 mmol/L |
| 1 hour after glucose drink | ≥ 10.0 mmol/L |
| 2 hours after glucose drink | ≥ 8.5 mmol/L |
If any one of the three results meets or exceeds the relevant threshold, you may be diagnosed with gestational diabetes following your doctor’s assessment [2].
Try not to interpret a result on your own before speaking with your healthcare team. Your doctor will consider your results alongside your overall pregnancy and health.
Does gestational diabetes mean I did something wrong?
No. Gestational diabetes is linked to changes in insulin sensitivity during pregnancy and can occur even when you have been eating well and staying active.
It is also more common than many first-time moms realise. NUH states that gestational diabetes affects about one in five pregnant women in Singapore [3].
What happens if you are diagnosed with gestational diabetes?
The next step is usually a conversation with your healthcare team about managing your blood glucose.
For many moms, management begins with changes to eating habits and regular physical activity. A dietitian may help you plan balanced meals, manage portions and spread meals more regularly throughout the day.
You may also be encouraged to stay active with pregnancy-appropriate exercise, such as walking, depending on your doctor’s advice.
Your healthcare team may ask you to monitor your blood sugar at home using a finger-prick test. This can involve checking your glucose before and two hours after meals, as well as at bedtime. The exact frequency depends on your individual situation and your doctor’s recommendations.
If diet and exercise are not enough to keep your blood glucose within your target range, medication may be recommended. This can include insulin and, in some cases, other medication.
The important thing is that gestational diabetes can be managed. Most women with well-controlled GDM can have healthy pregnancies and healthy babies [3].
What happens after pregnancy?
If you are diagnosed with gestational diabetes, you may need to continue monitoring after the baby is born.
Your doctor may recommend another OGTT six to 12 weeks after delivery to check whether your blood glucose has returned to the expected range [2] [3]. You may also be advised to continue regular diabetes screening every one to three years because having GDM increases your future risk of developing type 2 diabetes [2].
The OGTT is a checkpoint, not a judgement
An OGTT can feel daunting, particularly when you are already juggling appointments, scans and everything else that comes with pregnancy. Knowing what happens beforehand can make the process feel much less intimidating.
Remember to follow your clinic’s fasting instructions, bring something to occupy you during the waiting period and have a snack ready for afterwards. If your results show gestational diabetes, your healthcare team can guide you through the next steps and help you manage it throughout the rest of your pregnancy.
Frequently Asked Questions
1. When is the OGTT glucose test done during pregnancy?
The OGTT is usually done between 24 and 28 weeks of pregnancy in Singapore. Women with certain risk factors, such as previous gestational diabetes, prediabetes or a family history of diabetes, may be screened earlier [2] [3].
2. Can I drink water before an OGTT?
Generally, plain water is allowed during the fasting period, but you should follow the specific instructions given by your hospital or clinic. Avoid food and other drinks unless your healthcare provider tells you otherwise [1] [3].
3. What happens if I fail the OGTT during pregnancy?
If one or more of your OGTT readings meet or exceed the Singapore diagnostic thresholds, your doctor may diagnose gestational diabetes. You will then receive guidance on diet, physical activity and blood glucose monitoring, with medication added if needed [2] [3].
4. What are the normal OGTT levels in pregnancy in Singapore?
For Singapore’s three-point OGTT, the gestational diabetes thresholds are 5.1 mmol/L or higher when fasting, 10.0 mmol/L or higher at one hour, and 8.5 mmol/L or higher at two hours. Meeting or exceeding any one threshold may lead to a diagnosis after your doctor’s assessment [2].
5. How long does the OGTT take during pregnancy?
The test usually takes around two to three hours, including the initial fasting blood test, the glucose drink and blood tests one and two hours afterwards [2]. Plan to stay at the clinic for the full duration and bring something to keep yourself occupied.
References
- Thomson Medical. Oral Glucose Tolerance Test (OGTT), What Do You Need to Know. Accessed 2 September 2026. https://www.thomsonmedical.com/blog/oogt
- HealthHub. Parent Hub: We’re Expecting, Gestational Diabetes. Accessed 2 September 2026. https://www.healthhub.sg/programmes/parent-hub/pregnancy/gestational-diabetes
- National University Hospital. Gestational Diabetes. Accessed 2 September 2026. https://www.nuh.com.sg/health-resources/diseases-and-conditions/gestational-diabetes
