Glucose screening checks for gestational diabetes, a short-term form of diabetes that some women develop during pregnancy. It's becoming more common in the United States, affecting about 6% to 7% of pregnancies.
The test is usually done at 24 to 28 weeks, but sometimes earlier if a woman is at higher risk for gestational diabetes.
Why Is Prenatal Glucose Screening Done?
Glucose screenings check for gestational diabetes. It's important to diagnose the condition because it can cause health problems in a newborn baby, especially if it's not treated.
What Happens During a Glucose Screening?
If you have this screening test, you'll drink a sugary liquid, then have a blood test an hour later to check your glucose levels. If the level is high, you'll have a glucose-tolerance test. For this test, you'll drink a glucose solution on an empty stomach and have your blood drawn once every hour for 3 hours.
Should I Have a Glucose Screening?
Most pregnant women have this test. If they have gestational diabetes, it's treated to reduce the risk to the baby.
When Are Glucose Screenings Done?
Screening for gestational diabetes usually is done at 24 to 28 weeks. It can be done earlier for women who are at higher risk for the condition, such as those who:
- have previously had a baby who weighed more than 9 pounds (4.1 kilograms)
- have a family history of diabetes
- are obese
- are older than age 25
- have sugar in the urine (pee) on routine testing
- have high blood pressure (hypertension)
- have polycystic ovary syndrome (PCOS)
When Are the Results Available?
The results are usually available within 1 to 2 days. Ask if your health care provider will call you with the results if they are normal or only if the reading is high (in which case, you'll you need to come in for another test).
Gestational diabetes (GD) is a type of diabetes that occurs during pregnancy. It happens when your body is not able to produce enough insulin to keep the amount of glucose (sugar) in your blood at proper levels. Untreated GD increases the likelihood of having a large baby, and is associated with birth complications as well as health risks for the newborn (e.g., preeclampsia, shoulder dystocia). Untreated GD also increases the risk of stillbirth late in pregnancy (36-40 weeks). Women who develop GD are at higher risk of developing type 2 diabetes in the future. However, there is excellent treatment for GD, and most women diagnosed with GD have normal deliveries and healthy babies.
Why is it important to screen for gestational diabetes?
All pregnant women should be offered blood glucose screening for GD between 24 and 28 weeks of pregnancy. If you have risk factors for GD, you will be tested earlier in your pregnancy. These risk factors include:
- Being older than 35
- Obesity (defined as a pre-pregnancy BMI greater than 30)
- Aboriginal, African, Asian, Hispanic, or South Asian ethnicity
- Family history of diabetes
- Polycystic ovarian syndrome or acanthosis nigricans
- Corticosteroid use during pregnancy
- Previous pregnancy with GD
- Previous delivery of a baby large than 4000 g
What does the blood glucose test involve?
All pregnant women are offered this screening test between 24-28 weeks gestation. When other risk factors are present, such as obesity, the test may be offered earlier and then repeated if initially normal. The screening test for GD is called a ‘glucose challenge’, which aims to see how your body is handling sugars. The measurement is taken 1 hour after you consume a glucose drink. This test can be conducted at any time of day as it is not a fasting test. If your blood sugar is normal after the challenge, you will not require any more testing. If it is high, you will have a second test. This test is done in the morning while you are fasting and will require you not to eat prior to the test. You will have your glucose tested before consuming a glucose drink and then tested again 1 and 2 hours later. If your glucose is higher than specific cut-off values, it means you have GD. See the table for more specific information.
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Screening for gestational diabetes |
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Step 1 – non fasting, 50 g glucose challenge |
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| 1 hour | Less than 7.8 mmol/L = no further testing Between 7.8 and 11.1 mmol/L, go to step 2 Higher than 11.1 mmol/L = GD |
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Step 2 – fasting, 75 g glucose challenge |
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Fasting |
Higher than 5.3 mmol/L = GD |
| 1 hour | Higher than 10.6 mmol/L = GD |
| 2 hour | Higher than 9.0 mmol/L = GD |
What if I have gestational diabetes?
GD is increasingly common, with about 7% of women having the condition. If you are found to have GD, you will work closely with your health care provider(s) to keep your blood glucose levels in a healthy range. This involves choosing a healthy diet, gaining the recommended weight during your pregnancy, getting exercise, and if needed, taking insulin or pills to lower your blood sugar. Your baby’s wellbeing will be carefully monitored by regular measurements of growth and amniotic fluid volume. If you have GD you will be offered a repeat glucose tolerance test between 6 weeks and 6 months postpartum to detect prediabetes and diabetes. You may also be offered induction between 38-40 weeks of pregnancy. Finally, it is strongly recommended that women with GD breastfeed their infants.
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About 1 in 10 women is diagnosed with gestational diabetes during her pregnancy — that's a big percent of all moms by any means. Undetected and untreated, gestational diabetes can up the risk of complications, but it’s easily managed once diagnosed. The glucose screening and glucose tolerance test can detect this condition and get moms the special attention they need throughout the rest of their pregnancies.
With that said, research suggests that about 15 percent of women get a false-positive result on their glucose screening. In other words, they test positive for elevated blood sugar levels on their glucose screening, but they don’t actually have gestational diabetes.
So why the discrepancy between the test result and number of women who actually have the condition? Often, women test positive simply because of what they ate in the hours before the test. Here’s what to eat before your glucose test to help ensure you get the most accurate results.
What to eat before the glucose test
When you eat, your body breaks down carbs into glucose, which is your body’s main source of energy. During pregnancy, two types of tests check your blood glucose (sugar) levels to detect and diagnose gestational diabetes. Each requires a different eating strategy.
Glucose screening
Between weeks 24 to 28 of each pregnancy (possibly sooner, if you’re at a higher risk of gestational diabetes), your doctor will conduct a glucose screening, usually in the morning. For this test, also known as the two-step test or one-hour glucose test, you’ll drink a sugary beverage and have your blood drawn an hour later to check the glucose levels in your blood.
While you might think that not eating at all before your test can increase the odds of passing, don't make the mistake of skipping breakfast. Doing so may actually throw your sugar levels out of whack. Instead, you should eat a meal with a balance of healthy carbs and protein the night before and the morning of your glucose screening.
Foods that serve up “good" or "complex" carbs are higher in fiber and take longer for your body to digest. They enter your bloodstream more gradually, so you won’t experience blood sugar spikes. Foods that contain complex carbs include:
- Whole grains, like whole-wheat bread and oatmeal
- Vegetables, including non-starchy veggies like tomatoes, cucumbers, broccoli, leafy greens and green beans
- Fresh fruit, such as berries, apples and watermelon
- Legumes, such as chickpeas, black beans, kidney beans and lentils
For long-lasting energy, balance your meal with protein-filled foods such as dairy, nuts, fish or lean meat like poultry.
Examples of healthy breakfasts during pregnancy that will help you pass the glucose test include:
- Whole wheat toast topped with natural peanut butter or mashed avocado
- Plain Greek yogurt with blueberries
- Oatmeal made with low-fat milk and topped with fresh berries
- Broccoli and cheddar cheese omelet
- Tofu scramble with spinach and Swiss cheese
- Whole wheat burrito filled with scrambled eggs, beans and tomatoes
It’s also a good idea to watch what you eat before your regular doctor appointments. That’s because every time you visit your doctor, you’ll likely have to pee in a cup so your care team can check the sugar levels in your urine — a sign that you may have gestational diabetes. Similar to the glucose screening, it’s possible to get a positive result if you just ate a sugary meal, even if you don’t have gestational diabetes.
Glucose tolerance test
If your blood sugar levels on the glucose screening are too high, it could mean your body isn’t producing enough insulin to process the extra glucose in your system during pregnancy. You may need to go back for a glucose tolerance test (sometimes called the one-step test or three-hour glucose test).
For this test, you’ll have your blood drawn after fasting beforehand. You’ll then drink a sugary drink and have your blood drawn three more times at one, two and three hours later.
For the glucose tolerance test, you'll need to avoid eating for eight to 14 hours before your scheduled appointment.
How to pass the glucose screening
For the best results, try to:
Eat breakfast
Before the glucose screening, eat a meal that includes both complex carbohydrates and protein. (Remember, if you’re doing the glucose tolerance test, you’ll need to fast for eight or so hours beforehand. Not sure which test you’re taking? Confirm with your doctor.)
Avoid sugars and refined carbs
Don’t eat high-sugar foods or simple carbs (including refined grains) the morning of your glucose screening. The body breaks these foods down quickly, leading to a spike in blood sugar levels. That means avoiding foods such as:
- Orange juice and other fruit juices
- Sugary granola
- Refined cereal
- Sugary toppings like jam or syrup
- Pancakes
- Doughnuts
- White bread
- Many other sweetened baked goods made with refined white flour, such as banana bread, croissants or muffins
Take a walk
If you can, try to squeeze in a 10- to 15-minute walk after your meal, which can help get your blood sugar levels in check.
If you don’t pass the glucose screening
On your glucose screening or regular urine tests, it’s possible to get a positive test result that your doctor considers to be "medically insignificant" — meaning that there is no effect on your growing baby. It’s still a good reminder to ask your doctor for healthy eating tips.
If your test does come back positive and you are ultimately diagnosed with gestational diabetes, remember that the condition is easily managed and goes away soon after you give birth. In the meantime, your doctor will ask you to monitor your blood sugar and offer strategies to help keep your levels stable, including cutting back on sugary, processed foods and loading up on complex carbs and other pregnancy-friendly foods.
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- Centers for Disease Control and Prevention, Diabetes and Pregnancy: Gestational Diabetes, July 2020.
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- University of San Francisco, UCSF Health, Dietary Recommendations for Gestational Diabetes, 2021.
- U.S. Department of Agriculture, MyPlate: Grains, 2021.
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