Pregnancy
Glucose Test in Pregnancy: 1-Hour vs 3-Hour Test, How to Prepare and What Results Mean
The pregnancy glucose test checks for gestational diabetes, a type of diabetes that develops during pregnancy. Most people take it between 24 and 28 weeks. In the U.S., the usual approach is a 1-hour screening test; if that number comes back high, you take a 3-hour diagnostic test. Failing the 1-hour screen is common and does not mean you have diabetes.
Ask anyone who's done it and you'll hear the same things: the drink is very sweet, the hour drags, and the 3-hour version is mostly a test of patience. Here's what to expect so it's not a surprise.
Why everyone gets tested
Hormones from the placenta make your body more resistant to insulin. Most people make enough extra insulin to keep blood sugar normal. When the body can't keep up, blood sugar rises, and that's gestational diabetes.
It usually has no symptoms, which is why everyone is screened. Untreated, it raises the chance of a very large baby, birth injuries, C-section, preeclampsia and low blood sugar in the newborn. Treatment lowers those risks. More in our gestational diabetes guide.
Who gets tested earlier?
Your provider may test you in the first trimester if you have a higher BMI (25 or higher, or 23 or higher if you're Asian American) plus another risk factor, such as:
- Gestational diabetes in a previous pregnancy
- A parent or sibling with diabetes
- High blood pressure or polycystic ovary syndrome (PCOS)
- A previous baby weighing more than about 9 pounds
- Prediabetes or a high A1C
- Being from a racial or ethnic group with higher diabetes rates
If the early test is normal, you'll usually be retested at 24 to 28 weeks.
The 1-hour test, step by step
This is the screening step of the common "two-step" approach.
- You get the drink. It has 50 grams of sugar and you usually finish it within 5 minutes. It tastes like very sweet flat soda, usually orange, lemon-lime or fruit punch. Chilled is easier. Drink it steadily; don't nurse it.
- You wait one hour. No eating, and most labs ask you to stay put rather than walk around, because activity can change the result. Bring a book, headphones or work. Set a timer and tell the front desk when you finished the drink.
- One blood draw. That's it.
You usually don't have to fast for the 1-hour test, but follow your practice's instructions. If your result is above the practice's cutoff, you'll be scheduled for the 3-hour test. Practices use slightly different cutoffs, so ask what number yours uses.
The 3-hour test, step by step
This is the diagnostic test, and it's a commitment. Book the first slot of the morning and clear the morning.
- Fast overnight, typically 8 to 14 hours. Water is usually fine.
- First blood draw to check your fasting sugar.
- A stronger drink with 100 grams of sugar.
- Blood draws at 1, 2 and 3 hours. Four sticks in total. If your veins are tricky, tell the phlebotomist early.
You're generally diagnosed with gestational diabetes if two or more of the four values are high. If only one is high, your provider may suggest extra monitoring or a repeat test later.
Many people feel shaky, nauseated or wiped out by hour two. Tell the staff if you feel faint. If you vomit the drink, the test usually has to be rescheduled.
The one-step alternative (2-hour, 75 grams)
Some practices use a single 2-hour test instead. You fast, have a blood draw, drink 75 grams of glucose, and have blood drawn at 1 and 2 hours. With this test, one high value is enough for a diagnosis. Both approaches are accepted; ACOG has historically favored the two-step method, and the American Diabetes Association accepts either.
Side by side
| 1-hour (screen) | 3-hour (diagnostic) | 2-hour (one-step) | |
|---|---|---|---|
| Glucose drink | 50 g | 100 g | 75 g |
| Fasting needed | Usually no | Yes | Yes |
| Blood draws | 1 | 4 | 3 |
| Diagnosis if | Screen only | 2 or more high values | 1 or more high values |
What to bring
- A protein snack and water for the minute you're done (cheese, nuts, a sandwich)
- Something to pass the time
- A sweater; lab waiting rooms are cold
- Your lab order and insurance card
- On the 3-hour day, someone to text, because you will want to complain
Don't try to "beat" the test
A common question: should I cut carbs for a few days before so I pass? Don't. The goal is an accurate answer. Changing your diet drastically right before can skew results, and missing gestational diabetes can affect your baby. Eat normally unless your practice tells you otherwise.
Jelly beans and other swaps
People ask about jelly beans constantly. Alternatives like that haven't been validated as a replacement for the standard drink, so most providers don't offer them. If you truly can't tolerate the drink, ask about options.
If you've had bariatric surgery
The glucose drink can cause "dumping syndrome" after some weight-loss surgeries, with cramping, dizziness and diarrhea. Tell your provider; you may be asked to check your blood sugar with a fingerstick meter for a week or two instead.
Why so many people fail the 1-hour screen
The 1-hour screen casts a wide net so it catches most people who might have gestational diabetes. The trade-off is that it flags many people who turn out to be fine. Many people who fail the 1-hour go on to pass the 3-hour. A high screening number is a reason to test further, not a diagnosis.
If you're diagnosed
Most people manage gestational diabetes with diet changes, physical activity and checking blood sugar at home several times a day. Some need medication, most often insulin. You'll likely meet a diabetes educator or dietitian, and you may have extra ultrasounds or fetal monitoring late in pregnancy. Some people are referred to a maternal-fetal medicine specialist to help manage it.
Gestational diabetes usually goes away after birth, but it raises your risk of type 2 diabetes later. You'll be asked to have a glucose test after delivery and regular screening after that. Put that postpartum test on the calendar; it's the one people most often skip.
Is it covered in New York?
Gestational diabetes screening is a recommended preventive service in pregnancy, so it's covered by most insurance plans, including NY Medicaid. If you're uninsured, NY Medicaid covers pregnant people with incomes up to 223% of the federal poverty level, and you can apply as soon as you know you're pregnant.
When to call your provider
Call your provider if:
- You're past 28 weeks and haven't been offered glucose testing
- You vomit the drink or feel too unwell to finish the test
- You have very frequent urination with extreme thirst, blurry vision or unusual tiredness
- You've been diagnosed and your home readings are often above the targets you were given
To find an OB/GYN who can manage blood sugar in pregnancy, search the directory or browse OB/GYNs in Staten Island.
Frequently asked questions
When is the glucose test done in pregnancy?
Most people are screened between 24 and 28 weeks. If you have risk factors for diabetes, such as a higher BMI plus other risks or a history of gestational diabetes, your provider may test you earlier in pregnancy.
Do I need to fast for the 1-hour glucose test?
Usually not. The 1-hour screening test is generally done without fasting, but some practices give their own instructions. The 3-hour test does require fasting overnight, so follow your provider's directions.
What happens if I fail the 1-hour glucose test?
A high 1-hour result is common and does not mean you have gestational diabetes. It means you need a longer diagnostic test, usually the 3-hour glucose tolerance test, to know for sure.
Can I eat jelly beans instead of drinking the glucose drink?
Alternatives like jelly beans haven't been validated as a replacement for the standard glucose drink, so most providers don't offer them. If you can't tolerate the drink or have had weight-loss surgery, ask your provider about other options.
Sources
- ACOG — Gestational Diabetes Mellitus (Practice Bulletin 190)
- ACOG — Gestational Diabetes FAQ
- USPSTF — Screening for Gestational Diabetes
- American Diabetes Association — Standards of Care in Diabetes: Management of Diabetes in Pregnancy
This article is for general education and is not medical advice. It does not replace an evaluation by a licensed clinician who knows your history. If you think you have a medical emergency, call 911.