Oral glucose tolerance test (OGTT)
Quick answer: A glucose tolerance test measures your blood sugar while fasting and then at set times after you drink a measured glucose solution. Doctors order it to diagnose gestational diabetes in pregnancy, or diabetes and prediabetes when other results are unclear.
- SampleBlood
- Takes2 to 3 hours with timed samples
- Before the testFast for 8 to 10 hours (water is fine), eat normally in the days before, and plan to stay at the lab for 2 to 3 hours without eating, smoking or walking about.
- In fertility careThe OGTT is the standard test for gestational diabetes, which needs treatment to protect mother and baby.
How the test is done
- 1You come in the morning after an 8 to 10 hour fast
- 2A fasting blood sample is taken
- 3You drink a measured glucose solution within about 5 minutes
- 4More samples are taken at set times while you stay seated
What your results can mean
Reading your report
Cut-offs differ between guidelines and in pregnancy, so discuss your result with your doctor.
If the result is outside the usual range
A high fasting or later reading can be seen with gestational diabetes, diabetes or prediabetes. A low reading after the drink is uncommon and can cause shakiness, which you should tell staff about.
Who usually has this test
Pregnant women, usually at 24 to 28 weeks or earlier if at risk, and people whose fasting sugar or HbA1c results are unclear.
Risks and aftercare
You may feel a little sick or tired; eat a meal once the last sample is taken.
Names and options
Also called: GTT, OGTT, 75 g glucose test, sugar tolerance test
Options
- 3 samples
- 4 samples
Listed by the hospital as
- GTT 4 (GLUCOSE TOLERANCE TEST,)
- GTT 3 (GLUCOSE TOLERANCE TEST,)
Where this test fits in fertility care
- 1Fertility work-up
- 2Screening before IVF or IUI
- 3During treatment
- 4After embryo transfer
- 5Pregnancy check-upsThis test
- 6If treatment has not worked
The usual order. See every test at each stage →
Questions about this test
How long does a glucose tolerance test take?
Plan for 2 to 3 hours. Blood is taken fasting, and again at set times after the glucose drink. You should stay seated and not eat during this time.
Why is the GTT done in pregnancy?
Pregnancy hormones can raise blood sugar, causing gestational diabetes. The test is often done between 24 and 28 weeks, or earlier if you have risk factors such as PCOS or a family history of diabetes.
What if I feel sick during the glucose tolerance test?
Tell staff right away. If you vomit, the test usually needs to be repeated on another day.
Related tests
Tamara Hospital & IVF Centre, Rajajinagar
34/3, 10th Cross Road, opp. Vardhaka Sardar Patel School, 1st N Block, 2nd Stage, Rajajinagar, Bengaluru 560010
The hospital is open 24 hours. Call before you come to check the timing for your scan or sample collection.
Get directions ↗IVF Pulse fertility care at Tamara Hospital →
Reception
Waiting area
IVF lab
This page explains each test in general terms so you know what to expect. It is not medical advice: your doctor decides which tests you need and what your results mean. Reference ranges differ between laboratories. Updated 4 November 2026.