Gestational diabetes glucose test results: what the numbers mean
Gestational diabetes is high blood sugar that starts or is found during pregnancy. It is checked with a glucose drink and one or more blood draws. There are two common ways to test, and each uses its own cut-offs. (MedlinePlus) (USPSTF, 2021)
Who is tested and when
- USPSTF: recommends screening for gestational diabetes in pregnant people without symptoms at 24 weeks of pregnancy or later (grade B, 2021), one time. It found the evidence insufficient to weigh the benefits and harms of screening before 24 weeks (I statement). (USPSTF, 2021)
- ADA: screen at 24 to 28 weeks anyone not already found to have diabetes or high-risk blood sugar earlier in the pregnancy. (ADA, 2026)
- ACOG: all pregnant people should be screened. People with risk factors are tested early in pregnancy; everyone else between 24 and 28 weeks. (ACOG)
- NICE and the NHS (UK): testing is offered to people with a risk factor, such as a BMI of 30 or more, a previous baby weighing 4.5 kg or more, gestational diabetes before, a parent or sibling with diabetes, or a family background with a high rate of diabetes. (NICE NG3) The NHS also lists being over 40 and past weight-loss surgery. (NHS)
Where this test sits among the other checks in pregnancy: pregnancy screenings by week.
The two ways to test
- Two-step: first a 1-hour screening test. You drink a liquid with 50 g of glucose, with no need to fast, and blood is drawn 1 hour later. If that result is high, you come back for a 3-hour test: after 8 to 14 hours with nothing to eat or drink except sips of water, you drink 100 g of glucose and blood is drawn before and then every hour for 3 hours. (MedlinePlus)
- One-step: a single 2-hour test. After the same fast, you drink 75 g of glucose and blood is drawn before and then at 1 and 2 hours. (MedlinePlus) The ADA says it is done in the morning after an overnight fast of at least 8 hours. (ADA, 2026)
- How it feels: the drink tastes like a very sweet soda. Some people feel sick, sweaty or lightheaded afterwards; serious side effects are very uncommon. Eat your normal food in the days before, and ask your provider whether any medicine you take can affect the result. (MedlinePlus)
For more on fasting before blood tests in general: fasting before a blood test.
The 1-hour screening test (step 1)
A result at or above the cut-off sends you on to the 3-hour test. Practices use one of three cut-offs: ACOG accepts any of 130, 135 or 140 mg/dL (7.2, 7.5 or 7.8 mmol/L). (ADA, 2026) (USPSTF, 2021) A lower cut-off sends more people to the longer test.
| Cut-off your practice uses | Screen negative | Go on to the 3-hour test |
|---|---|---|
| 130 mg/dL | Below 130 mg/dL | 130 mg/dL or higher |
| 135 mg/dL | Below 135 mg/dL | 135 mg/dL or higher |
| 140 mg/dL | Below 140 mg/dL | 140 mg/dL or higher |
A high 1-hour result is not a diagnosis. MedlinePlus says about 2 out of 3 people who take the 3-hour test do not have gestational diabetes. (MedlinePlus)
The diagnostic tests: 3-hour and 2-hour values
Each number is a cut-off: a value at or above it counts as high. The two-step test needs 2 or more high values; the one-step test needs only 1. (USPSTF, 2021) (ADA, 2026)
| Test and criteria | Fasting | 1 hour | 2 hours | 3 hours | Diagnosis if |
|---|---|---|---|---|---|
| Two-step, Carpenter and Coustan (100 g, 3 hours) | 95 mg/dL (5.3 mmol/L) | 180 mg/dL (10.0 mmol/L) | 155 mg/dL (8.6 mmol/L) | 140 mg/dL (7.8 mmol/L) | 2 or more values at or above the cut-off (USPSTF, 2021) (ADA, 2026) |
| Two-step, NDDG (100 g, 3 hours) | 105 mg/dL | 190 mg/dL | 165 mg/dL | 145 mg/dL | 2 or more values at or above the cut-off (USPSTF, 2021) |
| One-step, IADPSG (75 g, 2 hours) | 92 mg/dL (5.1 mmol/L) | 180 mg/dL (10.0 mmol/L) | 153 mg/dL (8.5 mmol/L) | Not measured | 1 or more values at or above the cut-off (USPSTF, 2021) (ADA, 2026) |
- Carpenter and Coustan vs NDDG: both read the same 3-hour test, but each fasting and timed cut-off is higher under NDDG. (USPSTF, 2021)
- One high value on the 3-hour test: Carpenter and Coustan needs 2, but ACOG notes that 1 high value can be used for the diagnosis. (ADA, 2026)
- NICE (UK): uses the 75 g 2-hour test and diagnoses gestational diabetes with a fasting value of 5.6 mmol/L or above, or a 2-hour value of 7.8 mmol/L or above. (NICE NG3)
Where they differ: the ADA recommends the one-step IADPSG criteria to improve pregnancy outcomes, because they are the only criteria based on pregnancy outcomes, while still listing the two-step test as an option. (ADA, 2026) A 2013 NIH panel favored keeping the two-step approach, pointing to a lack of trials showing benefit from the one-step test, the 1-hour test needing no fasting, and the downsides of diagnosing many more people, including more health care use and costs. The USPSTF's 2021 review found one-step testing made a diagnosis more often (11.5% vs 4.9%) without better health outcomes. (ADA, 2026) The USPSTF accepts either approach. (USPSTF, 2021)
A screening result is not a diagnosis on its own. Your doctor decides what your result means for you.
Testing early in pregnancy
- ADA: before 15 weeks, test people with risk factors for diabetes that was there before pregnancy, using the usual non-pregnancy cut-offs, and consider testing everyone. It also flags an A1C of 5.9% to 6.4% or a fasting glucose of 110 to 125 mg/dL early in pregnancy as a sign of higher risk. The one-step and two-step cut-offs above were not built for early pregnancy and should not be used then. If early tests are normal, test again at 24 to 28 weeks. (ADA, 2026)
- USPSTF: evidence on screening before 24 weeks is insufficient. It notes that some people are screened earlier because of risk factors such as obesity, a family history of type 2 diabetes or a large baby in a past pregnancy. (USPSTF, 2021)
- NICE and the NHS: after gestational diabetes in a past pregnancy, testing is offered soon after the booking appointment and again at 24 to 28 weeks if the first result is normal. (NICE NG3) (NHS)
The non-pregnancy A1C and glucose ranges are on A1C and blood sugar test results.
The recheck after birth
- ADA: people who had gestational diabetes should have a 75 g glucose tolerance test 4 to 12 weeks after birth, read with the non-pregnancy cut-offs, and lifelong screening every 1 to 3 years. (ADA, 2026)
- ACOG: a blood test 4 to 12 weeks after birth; if it is normal, a diabetes test every 1 to 3 years. (ACOG)
- NICE: a fasting blood glucose test 6 to 13 weeks after birth rather than a routine glucose tolerance test, then a yearly HbA1c test if the result is normal. (NICE NG3)
Gestational diabetes usually goes away after birth, but people who had it have a higher risk of diabetes later in life. (ACOG) This page does not cover treatment, diet plans or blood sugar monitoring; your care team guides those.
Questions people ask
I failed the 1-hour glucose test. Do I have gestational diabetes?
Not from that test alone. The 1-hour test is a screening step, and a high result leads to a longer test that makes the diagnosis. MedlinePlus says about 2 out of 3 people who go on to take the 3-hour test do not have gestational diabetes. Your doctor decides what your result means for you. (ADA, 2026) (MedlinePlus)
What is the cut-off for the 1-hour glucose test?
It depends on the practice. ACOG accepts any of the common cut-offs of 130, 135 or 140 mg/dL, measured 1 hour after a 50 g glucose drink. A result at or above the cut-off your practice uses means you are sent for the 3-hour test. (ADA, 2026) (USPSTF, 2021)
Do I need to fast for the glucose test in pregnancy?
Not for the 1-hour screening test. For the 3-hour 100 g test and the 2-hour 75 g test, MedlinePlus says nothing to eat or drink except sips of water for 8 to 14 hours before, and no eating during the test. Eat your normal food in the days before. (MedlinePlus)
What if only one number on my 3-hour test is high?
Under the Carpenter and Coustan criteria the diagnosis needs 2 or more values at or above the cut-offs. ACOG notes that 1 high value can be used for the diagnosis. Practices differ, so your doctor decides what your result means for you. (ADA, 2026)
Will I be tested again after the baby is born?
If you had gestational diabetes, yes. The ADA and ACOG advise a test 4 to 12 weeks after birth, and the ADA then advises screening every 1 to 3 years for life. NICE advises a fasting blood glucose test 6 to 13 weeks after birth and a yearly HbA1c test if it is normal. (ADA, 2026) (ACOG) (NICE NG3)