So, you’ve just done the one hour glucose test (often called the glucose screening or 1-hour glucose tolerance test) — and now you’re staring at your test results thinking: Wait… do I have gestational diabetes? Do I need the three hour test?
Take a breath. You’re not alone, and “failing” the 1-hour test does not automatically mean you’re called gestational diabetes / diagnosed with gestational diabetes mellitus. The 1-hour test is a screening. The 3-hour test is the one that’s used for diagnosis (the full oral glucose tolerance test).
Below is a simple breakdown of the 1 hr vs 3 hr glucose test, what happens during the entire test, and how to prepare so it feels less stressful.
1-hour glucose test (screening): A quick check to see if you might be at an increased risk for gestational diabetes.
3-hour glucose tolerance test (diagnosis): A longer glucose tolerance test that measures your blood glucose levels over time to confirm (or rule out) gestational diabetes mellitus.
If your 1-hour blood sugar number is elevated, your doctor may recommend additional testing — usually the three hour test.
Quick note: In some clinics, a very high one hour glucose test result (often 200 mg/dL or above) may be treated as high enough to diagnose gestational diabetes without doing the three hour test — or they may move straight to GD education and monitoring. But protocols vary a lot by provider, lab, and country, so always ask your care team what their cutoff is and what they recommend for additional testing.
1-hour test: You’re there for about one hour (plus check-in time).
3-hour test: You’ll be there for three hours (often longer with waiting and lab timing), so plan for enough time.
During the 3-hour test, you’ll usually need to sit quietly (no walking around the building, no errands), because movement can affect your blood sugar level.
Both tests involve a glucose drink — a very sweet glucose solution (basically a sweet liquid / glucose solution you drink quickly).
1-hour glucose test: typically 50g glucose
3-hour test: typically 100g glucose
It can taste like a flat, syrupy soda — think soft drinks, but sweeter.
This is one of the biggest “wait, what?” differences in the 1 hr vs 3 hr glucose test.
1-hour screening: often no fasting required (some clinics still give instructions — follow your lab/doctor).
3-hour test: usually requires fasting (often 8–12 hours). Your first number is a fasting blood sugar measurement.
Your provider may also give guidance for the days prior (for example, eating normally and not suddenly cutting all carbohydrates). Always follow your medical care instructions.
1-hour test:
Drink the glucose solution
One blood draw / blood sample at the 1-hour mark
3-hour glucose tolerance test:
First blood sample (fasting)
Drink the glucose drink
Then they draw blood every hour for three hours (so usually 4 total draws)
Each draw measures your blood glucose / blood sugar at that time point.
Here’s what the three hour test often looks like:
You arrive fasting and they take your first blood sample (fasting level).
You drink the glucose drink within a set time.
You wait and they do a blood draw at one hour, two hours, and three hours.
You’ll usually be asked to sit quietly and not eat during the entire test.
After the last draw, you can eat.
Bring water for after, a snack for when you’re done, and something to do (book, headphones). Some people feel nauseous or shaky — and occasionally people can experience low blood sugar later, so it’s good to have food ready.
Your normal range depends on:
which guidelines your lab uses
the cutoffs your clinic follows (often based on guidance from groups like the American Diabetes Association and the American College of Obstetricians and Gynecologists — you may see references like practice bulletin / practice bulletin no in clinic materials)
Your provider will interpret your test results and tell you whether you passed, need additional testing, or meet criteria for diagnosis.
First: please don’t panic.
A high 1-hour screening result can happen for lots of reasons — and many people go on to pass the three hour test with normal numbers.
A “fail” on the 1-hour test just means your body’s ability to process the glucose drink needs a closer look.
Your doctor will guide next steps based on your result, your risk factors (like prior GD, family history of diabetes, PCOS, higher BMI, age, or smoke exposure), and your pregnancy history.
Worth knowing: Some providers consider a very high 1-hour glucose test result (often ≥200 mg/dL) enough to diagnose gestational diabetes without doing the 3-hour test. Others still prefer the full oral glucose tolerance test. Since clinic protocols vary, check with your care team about their cutoff and next steps.
If the 3-hour test confirms gestational diabetes, you still have so many options — and you can absolutely have a healthy pregnancy and a healthy baby.
Most GD management includes:
diet and diet changes (balanced meals, carbs paired with protein/fat/fiber)
movement (if approved)
monitoring blood glucose levels
sometimes insulin or medication, depending on what your care team recommends
The goal is not perfection — it's steady blood sugar to support you and baby.
Grab the GD Toolkit for gestational diabetes basics, common targets, meal ideas, shopping lists, and practical guides. Or check out our gestational diabetes video lessons for quick, supportive lessons on managing GD day by day.
And if you want real-life support and community, join our HIgedi group — it's a judgment-free space where mamas share meals, ask questions, and support each other through the GD journey. You're not alone. 💜
When it comes to the 1 hr vs 3 hr glucose test, remember:
The one hour glucose test is a screening — not a diagnosis.
The three hour test (the full oral glucose tolerance test) gives clearer answers.
Whatever the outcome, you’re not failing — you’re getting information so you and your doctor can make the best plan for your pregnancy.
If you have additional questions, bring them to your provider — your healthcare team is there for you.
1. Can I eat before the 1-hour glucose test?
Yes, the 1-hour glucose screening usually does not require fasting. You can eat normally beforehand. However, some clinics may give different instructions, so always check with your provider about whether you need to fast or follow any diet changes before your appointment.
2. Do I have to fast before the 3-hour glucose test?
Yes, the 3-hour glucose tolerance test typically requires fasting for 8–12 hours before your appointment (usually overnight). This means no food, no soft drinks, no juice—just water is usually okay. Your fasting blood sugar is the first measurement, so an empty stomach is important for accurate results.
3. How long does the entire 3-hour test actually take?
Plan for three hours plus check-in and lab time—so realistically 3.5 to 4 hours. Bring something to do, water for after, and a snack to eat once you're finished.
4. What should I do if my blood sugar feels low after the test?
Some people experience low blood sugar after the test (shaking, sweating, dizziness). Always have a snack ready for after your appointment. Eat something with carbohydrates and protein (like a sandwich, fruit with nut butter, or cheese and crackers). If you feel very unwell, let your lab staff know before you leave.
5. What if I "fail" the 1-hour glucose test—do I definitely have gestational diabetes?
No. A high result on the 1-hour glucose test means you need additional testing (the three hour test), but it does not mean you have gestational diabetes mellitus. Many people pass the 3-hour test with normal results. The 1-hour test is just a screening—not a diagnosis.
6. Can I take the test if I'm sick or stressed?
Illness and stress can affect your blood sugar level. If you're very sick (fever, vomiting), contact your provider—they may want to reschedule. Stress can also raise numbers slightly. Try to sit quietly and stay calm during the test. If you have risk factors (like prior GD or family history of diabetes), your provider will take that context into account.
7. Do I need to do anything special to prepare for the test?
Follow your provider's instructions. Generally: eat normally before the 1-hour test (unless told otherwise), fast before the 3-hour test, drink water as usual, wear comfortable clothes, bring your ID and insurance card, and plan for enough time. Avoid heavy exercise the days prior if possible. Some providers suggest eating balanced meals with carbohydrates, protein, and healthy fats in the days before—not suddenly changing your diet.
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