Glucose (1-Hour, 50 g Challenge Screen)
A first-step sugar test in pregnancy. Your blood sugar one hour after a 50 g sugar drink shows whether a longer test is needed.
AI-verified against cited sources. Awaiting expert reviewAlso called GCT, GLTLOINC 1504-0
Check your result
The usual range for Glucose Challenge (1 h) depends on sex. Choose female or male above to see where you stand.
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What it is
For the glucose challenge test you drink a sweet liquid that has 50 grams of glucose. A blood sample taken one hour later shows how well your body handles the sugar. You do not need to fast. It is usually done between 24 and 28 weeks of pregnancy as the first step of a two-step check for gestational diabetes, which is high blood sugar that starts during pregnancy.
Why it matters
This test helps your care team decide whether you need a longer diagnostic test, the 3-hour glucose tolerance test. A high result on the first step is not a diagnosis of gestational diabetes. It only means the longer test is needed. If gestational diabetes is found, you and your care team can manage your blood sugar to protect you and your baby.
If it’s high
A result at or above your clinic's cutoff (130, 135 or 140 mg/dL) means you will be offered the longer test. It does not mean you have gestational diabetes. Gestational diabetes often causes no symptoms, so the test is how it is found.
Common causes
- The hormone changes of pregnancy, which make the body less able to use insulin
- Eating or drinking something other than what the clinic allowed during the hour
- Gestational diabetes, which only the follow-up test can confirm
What can help
- Schedule the follow-up test your clinic recommends
- Ask how to prepare for the follow-up test. The ADA notes that cutting back on carbohydrates in the days before a glucose tolerance test can make results look falsely high
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
The usual range depends on sex. Choose women or men to see the one that applies.
- Women, pregnancy t2up to 139 mg/dL
Sources: American Diabetes Association (Diabetes Care), Labcorp
- Women, pregnancy t3up to 139 mg/dL
Sources: American Diabetes Association (Diabetes Care), Labcorp
Where a 1-hour result falls against the ADA and ACOG cutoffs of 130, 135 and 140 mg/dL
- Below 130: under all three common cutoffsbelow 130 mg/dL
- 130 to 139: over the lower cutoffs (130, 135) but under 140130 to under 140 mg/dL
- 140 and above: over all three common cutoffs; a diagnostic test usually follows140 and above mg/dL
If this applies to you
Glucose Challenge (1 h) means a little more for some people. Open the one that fits you.
Pregnant or postpartum
The ADA suggests screening for gestational diabetes at 24 to 28 weeks. In the two-step approach, this 1-hour glucose drink test comes first, and a high result leads to a longer glucose tolerance test.
What can affect your result
- Timing of the blood draw: 1 hour after the drink
- Which cutoff your clinic uses: 130, 135 or 140 mg/dL
- How far along you are: the test is usually done at 24 to 28 weeks
- What you eat or drink during the hour
- How quickly the blood sample is processed
- Timing matters: the blood sample is taken 1 hour after the glucose load, so the result is only meaningful if the draw is on time. Follow your clinic's instructions for the hour, including anything about eating, drinking and activity.
- A blood sample that sits with the cells for a while can read falsely low, because the cells use up glucose at about 5 to 7% per hour. Labs use special tubes or fast processing to prevent this.
- Early in pregnancy the ADA says these criteria were not derived from data in the first half of pregnancy and should not be used for early screening.
Any time of day. It is usually done between 24 and 28 weeks of pregnancy. A snapshot taken 1 hour after the sugar drink.
When to talk to a clinician
Follow up with your care team soon if your result is at or above their cutoff, so the next test can be scheduled. Call your clinician the same day if you cannot keep fluids down, or you feel very thirsty, unwell or confused.
Questions you could ask
- Do I have any risk factors that mean I should be tested earlier or again?
- Which cutoff and which range is the lab using for this result?
- Which cutoff does your clinic use, and how far above it was my result?
- When should I have the follow-up glucose tolerance test, and how should I prepare?
- What happens next if the second test is also high?
Questions people ask
Does a high result mean I have gestational diabetes?
No. A high result on this first step only means you need a longer diagnostic test, usually a 3-hour glucose tolerance test done after fasting. Gestational diabetes is diagnosed from that second test.
Why do clinics use different cutoffs, 130, 135 or 140?
Both the American College of Obstetricians and Gynecologists and the ADA accept any of the three. A lower cutoff sends more people on to the longer test, and a higher one sends fewer. Use the cutoff your clinic or lab gives you.
Do I need to fast for this test?
No. The ADA describes this first-step test as nonfasting. The follow-up 3-hour test is done after fasting, and your clinic will tell you how to prepare for it.
Show the science and sources
Units
- 1 mg/dL = 1 mg/dL
- 1 mg/dL = 0.05551 mmol/L
Open the Glucose Challenge (1 h) unit converter
For clinicians and researchers
The ADA Standards of Care (2026) describe the two-step strategy: Step 1 is a nonfasting 50 g glucose load test with plasma glucose at 1 hour, at 24 to 28 weeks in people not previously diagnosed with diabetes. If the 1-hour value is 130, 135 or 140 mg/dL (7.2, 7.5 or 7.8 mmol/L) or higher, a fasting 100 g OGTT follows (Step 2), and gestational diabetes is diagnosed when at least two of four values are met or exceeded (Carpenter-Coustan: fasting 95, 1 hour 180, 2 hours 155, 3 hours 140 mg/dL). ACOG recommends any of the commonly used thresholds of 130, 135 or 140 mg/dL. The alternative is the one-step 75 g OGTT; a 2021 USPSTF systematic review found gestational diabetes in 11.5% with one-step versus 4.9% with two-step screening, without improved health outcomes. The USPSTF recommends screening at 24 weeks or later (grade B) and found the evidence before 24 weeks insufficient. The ADA also reports that A1C at 24 to 28 weeks works less well than the glucose load test as a screen. Glycolysis in an unseparated sample lowers glucose by roughly 5 to 7% per hour (NACB/ADA 2011), so timely plasma separation or glycolysis-inhibiting tubes matter.
LOINC 1504-0 (primary), 14754-6, 20438-8. Specimen: serum-or-plasma.
Sources
- 2. Diagnosis and Classification of Diabetes: Standards of Care in Diabetes-2026, American Diabetes Association (Diabetes Care) (2026)
- Gestational Diabetes Screen (ACOG Recommendations) (test 102277), Labcorp
- Gestational Diabetes, National Institute of Diabetes and Digestive and Kidney Diseases
- Screening for Gestational Diabetes: US Preventive Services Task Force Recommendation Statement, JAMA (2021)
- Guidelines and recommendations for laboratory analysis in the diagnosis and management of diabetes mellitus, Diabetes Care (NACB and ADA) (2011)
- Glucose (PubChem compound 5793), PubChem, National Library of Medicine
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.