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Glucose Tolerance Test (OGTT): 75 g, 100 g, Prep and Cut-offs

By the Diabetes Blogs editorial teamLast reviewed

Sources: ADA Standards of Care in Diabetes—2026; ACOG Practice Bulletin 190; NIDDK; NIDDK (full list)

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

TestFasting?SamplesCut-offs (ADA, ACOG)
50 g screen (step 1 of two-step)No1 hourAt or above 130, 135 or 140 mg/dL goes on to the 100 g test
100 g test (step 2 of two-step)YesFasting, 1, 2, 3 hoursTwo or more at or above: 95/180/155/140 (Carpenter-Coustan) or 105/190/165/145 (NDDG)
75 g test (one-step)YesFasting, 1, 2 hoursOne or more at or above: 92/180/153 mg/dL
75 g test, not pregnantYes2 hours140 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)

Glucose unit

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.

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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

Last reviewed: by the Diabetes Blogs editorial team. Information only, not medical advice.

Related tools and guides

1-hour glucose test

The 50-gram screening test in pregnancy, and the ACOG cut-offs of 130, 135 and 140.

3-hour glucose test

The 100-gram diagnostic test, with Carpenter-Coustan and NDDG cut-offs side by side.

Gestational diabetes numbers

ADA pregnancy targets and a check of where a reading falls.

A1C of 5.7

What 5.7% means and what the CDC suggests next.