Glucose Tolerance Test (OGTT): 75 g, 100 g, Prep and Cut-offs
An oral glucose tolerance test (OGTT) measures your blood glucose before and after a measured sugar drink. In pregnancy it comes in 50, 75 and 100 gram versions, and the cut-offs differ for each. Only a clinician can interpret a result.
The versions at a glance
| Test | Fasting? | Samples | Cut-offs (ADA, ACOG) |
|---|---|---|---|
| 50 g screen (step 1 of two-step) | No | 1 hour | At or above 130, 135 or 140 mg/dL goes on to the 100 g test |
| 100 g test (step 2 of two-step) | Yes | Fasting, 1, 2, 3 hours | Two or more at or above: 95/180/155/140 (Carpenter-Coustan) or 105/190/165/145 (NDDG) |
| 75 g test (one-step) | Yes | Fasting, 1, 2 hours | One or more at or above: 92/180/153 mg/dL |
| 75 g test, not pregnant | Yes | 2 hours | 140 to 199 mg/dL is the prediabetes range; 200 or higher is the diabetes range |
Details: 1-hour test and 3-hour test. The ADA lists the one-step 75 gram test and the two-step 50 then 100 gram test as the two accepted approaches in pregnancy.
Compare 75 gram test values (pregnancy)
Nothing you type is stored or sent. This compares with published numbers; it is not a diagnosis.
How to prepare
- Fast for the fasting versions as your clinic instructs, and ask whether water is allowed.
- Eat as you usually do in the days before, unless told otherwise.
- Stay seated during the test. Walking or smoking can affect the result, so ask your clinic what is allowed.
- Bring a snack to eat afterward.
Outside pregnancy
The ADA diagnoses diabetes with a 2-hour value of 200 mg/dL (11.1 mmol/L) or higher on a 75 gram test, and describes 140 to 199 mg/dL (7.8 to 11.0 mmol/L) as the prediabetes range. A diagnosis needs confirmation by your clinician. After gestational diabetes, the postpartum test uses these non-pregnancy criteria.
Frequently asked questions
What is an oral glucose tolerance test?
An OGTT measures blood glucose before and after you drink a measured glucose solution. Outside pregnancy the ADA uses a 75 gram drink and a 2-hour value: 200 mg/dL or higher is in the diabetes range and 140 to 199 mg/dL is in the prediabetes range.
Do I fast for a glucose tolerance test?
Yes for the 75 gram and 100 gram versions, which start with a fasting sample. The 50 gram screening drink in pregnancy is non-fasting.
What is the difference between the 75 g and 100 g tests in pregnancy?
The 75 gram test is a one-step test with three samples, and one value at or above the cut-offs is enough. The 100 gram test follows a 50 gram screen, has four samples, and two values are needed. Your clinic uses one approach.
How long does it take?
The 75 gram test takes about two hours and the 100 gram test about three, plus the time to check in. The 1-hour screen takes about an hour.
Can I prepare by eating less sugar?
Do not change how you eat to try to pass the test. Eat as you normally do unless your clinic gives other directions, so that the result reflects your usual state.
Information only, not medical advice. Your care team may set different targets for you, and only a lab test ordered by a clinician can diagnose diabetes or prediabetes. See our medical disclaimer.
Sources
- ADA Standards of Care in Diabetes—2026, Section 2: Diagnosis and Classification
- ACOG Practice Bulletin 190: Gestational Diabetes Mellitus (2018; cut-offs as quoted in ADA Standards 2026, Section 2)
- NIDDK: Gestational Diabetes (reviewed May 2017)
- NIDDK: Diagnosis of Diabetes and Prediabetes
Last reviewed: by the Diabetes Blogs editorial team. Information only, not medical advice.
