Glucose Tolerance Test (GTT, 100 Grams)
The 100g GTT is a diagnostic test for gestational diabetes. After an overnight fast, blood sugar is measured fasting and at 1, 2, and 3 hours after drinking 100 grams of glucose solution.
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What the Glucose Tolerance Test (GTT, 100 Grams) test tells you
This is the longer, confirmatory step in the classic two-stage pathway for gestational diabetes. If the shorter, non-fasting glucose challenge screen came back above the laboratory's screening level, this is the test that settles whether gestational diabetes is actually present. It is a timed procedure rather than a single blood draw, and it takes most of a morning, so it helps to plan the appointment with that in mind.
The sequence is fixed. You arrive having fasted overnight and a first blood sample is taken before anything is drunk, establishing your starting point. You then drink the measured 100-gram glucose solution, and further samples are taken at set intervals over the following three hours: at one hour, at two hours and at three hours. You stay at the facility throughout, without eating, drinking anything but the water you are permitted, smoking or walking about, because all of those change how quickly glucose leaves the blood and would make the readings impossible to compare.
What this pattern of samples reveals is something a single measurement cannot: not just where your blood sugar starts, but how high it climbs after a large load and how promptly it comes back down. That curve is what distinguishes a pancreas comfortably keeping pace with the insulin resistance of pregnancy from one that is not. Importantly, the diagnosis rests on more than one of the timed readings sitting above the laboratory's limits, rather than on any single value, which is one reason the whole sequence has to be completed. Where gestational diabetes is confirmed, it is treated with diet, blood sugar monitoring and sometimes medication, and that treatment substantially reduces the risks to both mother and baby, which is the entire reason the pathway exists.
Performed after a positive GCT screening to confirm or rule out gestational diabetes.
- Confirming or excluding the diagnosis
The screening test only raises a question. This is the test that answers it, so that treatment is started only where it is genuinely needed.
- A curve, not a snapshot
Timed samples show how high blood sugar climbs and how quickly it returns, which a single measurement cannot reveal.
- Protecting the pregnancy
Identifying gestational diabetes allows diet, monitoring and treatment to begin in time to lower the risks for mother and baby.
- Avoiding unnecessary treatment
Many women who screen positive do not have gestational diabetes, and this test is what spares them a treatment plan they do not need.
Reasons your doctor may request the Glucose Tolerance Test (GTT, 100 Grams) test
Your doctor may order this test for any of the reasons below. Some are routine checks, others follow specific symptoms or an earlier result.
Confirming gestational diabetes
- A glucose challenge screening result above the laboratory's screening level during pregnancy.
- Strong clinical suspicion of gestational diabetes even where screening was borderline.
A previous pregnancy
- Gestational diabetes in a previous pregnancy, where a confirmatory test is planned directly.
- A previous unusually large baby or other features that raise concern about glucose handling in pregnancy.
Sugar found in the urine
- Sugar repeatedly found in the urine during antenatal checks.
There is no single figure to read here. The result comes back as a "Multi-parameter panel": your blood sugar is measured fasting, then again at set points over the hours after the glucose drink, and each value is judged against its own target. The diagnosis rests on the pattern across the timed samples rather than on any one reading. Values above target reflect a pancreas that cannot fully overcome the insulin resistance created by pregnancy hormones, diabetes that was present before the pregnancy but undiagnosed, or steroid treatment being taken at the time. Restricting carbohydrate in the days beforehand paradoxically worsens the readings, so eat your usual diet. The sequence has to be completed for the result to mean anything, and your doctor interprets the full set alongside your stage of pregnancy, your risk factors and your history.
Medically reviewed by Dr Nirupama Sabhapathy
This test is reported descriptively rather than on a numeric scale: each finding below explains what your report may say.
Blood sugar is measured at several time points (fasting and after the glucose drink). Each value is interpreted against its own target. See your detailed report.
Ranges are a guide: your physician interprets your result alongside your symptoms and history.
What a higher result can point to
- Gestational diabetes, in which the pancreas cannot fully overcome the insulin resistance created by pregnancy hormones.
- Type 2 diabetes that was present before the pregnancy but had not been diagnosed.
- Steroid treatment given during pregnancy, which raises blood sugar while it is being taken.
- Restricting carbohydrate in the days before the test, which paradoxically worsens the body's handling of the glucose load.
What a lower result can point to
- An exaggerated or delayed insulin response, which drives the level down in the later hours of the test.
- Previous stomach or weight-loss surgery, which speeds absorption of the sugar load and then its clearance.
- Glucose-lowering medicine taken before the test rather than after it.
These are possibilities, not diagnoses. A single value outside the reference range is interpreted alongside your symptoms, history and other tests: your doctor decides what it means for you.
What this test cannot tell you
- The test only works if the whole sequence is completed; leaving early, eating or being sick partway through means it usually has to be repeated on another day.
- It is demanding, requiring an overnight fast and several hours at the facility with repeated blood samples, which some women find difficult.
- It describes glucose handling at one point in pregnancy, so a result within the expected range does not guarantee blood sugar will remain so as the pregnancy advances.
- Illness, steroid treatment and carbohydrate restriction beforehand can all shift the readings, so context matters when your doctor interprets them.
Risks of the blood draw
- Mild bruising or brief soreness where the needle went in.
- Occasional lightheadedness, which settles after a few minutes of rest.
- Bleeding or infection at the site, which is rare with sterile single-use equipment.
- 1Fasting overnight is required; only plain water should be taken before the first sample.
- 2Several blood samples are taken at set intervals over three hours and you must stay at the facility throughout.
- 3Eat your normal diet, including your usual carbohydrate, in the days beforehand.
- 4The diagnosis depends on the pattern across the timed samples, not on any single reading.
- 5A confirmed diagnosis is manageable, and treatment is what protects both mother and baby.
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Frequently Asked Questions
Everything you need to know about the Glucose Tolerance Test (GTT, 100 Grams) test. Can't find what you're looking for?
Talk to our team→The glucose challenge test is the shorter screening step for gestational diabetes. The 100 g glucose tolerance test is the diagnostic test that follows a positive challenge result: after an overnight fast, blood sugar is measured fasting and at 1, 2 and 3 hours after a 100 gram glucose drink, to confirm or rule out the diagnosis.
There is no single normal figure. Each timed reading, fasting and after the drink, is compared with its own target, and the targets are shown on your detailed report. The diagnosis rests on the pattern across the samples rather than any one value, so your doctor reads the full set with your stage of pregnancy and risk factors.
Tell the team straight away if you feel faint or nauseated at any point. If you vomit after the glucose drink, the test usually has to be rescheduled, because the full load has not been absorbed. Leaving early or eating partway through also means it normally has to be repeated on another day.
A reading that falls low in the later hours usually reflects an exaggerated or delayed insulin response to the sugar load. Previous stomach or weight-loss surgery can do the same by speeding absorption and then clearance, as can glucose-lowering medicine taken before the test rather than after it. Your doctor reads it with your history.
Yes, it is possible. The test describes how your body handles glucose at one point in pregnancy, and a result within the expected range does not guarantee blood sugar will stay there as the pregnancy advances. If new symptoms or risk factors appear, your doctor may decide to check again.
Because the useful information is in the shape of the response. Timed samples show how high blood sugar rises after the drink and how promptly it falls again. A single value cannot distinguish a pancreas that is keeping pace from one that is struggling.
Food adds more glucose, smoking and activity change how fast muscles take glucose out of the blood, and either would make your readings incomparable with the standard the test is judged against. Sitting quietly is part of the procedure, not just convenience.
No. Restricting carbohydrate in the days beforehand actually makes the body less efficient at handling the glucose load, which can push the readings higher. Eating your normal diet is the way to get an accurate result.
Your doctor will discuss a plan, which usually starts with dietary changes and home blood sugar monitoring, with medication added if needed. Most pregnancies affected by gestational diabetes proceed well once blood sugar is managed, and the condition commonly resolves after delivery.
Yes. Fast overnight, taking nothing but plain water, and come early in the morning. Plan to stay at the facility for about three hours after the drink, and eat your usual carbohydrate in the days beforehand.
The 100 g glucose tolerance test is AED 150, including a physician-reviewed report, with results usually within 24 hours. Home collection anywhere in Dubai is free when your order reaches AED 300 or includes a package; below that, a AED 100 home collection fee applies (AED 50 for a lab walk-in).