Oral Glucose Tolerance Test During Pregnancy
What are glucose screening tests during pregnancy?
Gestational diabetes is a common condition during pregnancy that affects up to 10% of pregnant people. It means you have too much glucose, or sugar, in your blood. A glucose screening checks for signs of gestational diabetes. A glucose test is how pregnancy care providers diagnose gestational diabetes. If left untreated, gestational diabetes can cause problems for both you and the fetus.
There are two types of glucose tests your provider will offer during pregnancy: A glucose challenge test and a glucose tolerance test.
The main difference is that the first test is a screening. It tells your provider that you may have gestational diabetes. If your results from the screening are abnormal, your provider orders a second test. The second test diagnoses gestational diabetes. Both tests involve drinking a sugary drink containing glucose and getting your blood drawn from a vein in your arm.
Glucose challenge test (glucose screening test)
The glucose challenge test is a screening, which means it detects an increased probability of gestational diabetes. This screening is a routine part of your prenatal care. An irregular result means there’s an increased chance you have gestational diabetes. However, it doesn’t diagnose gestational diabetes. People use many different names to refer to this first screening. Some other names are:
- Glucose screening.
- Gestational diabetes screening.
- One-hour glucose challenge test.
While people may use different terminologies, the important thing to know is that this first test is a screening. If you fail, it doesn’t mean you have gestational diabetes. It means your pregnancy care provider will recommend a second test to diagnose the condition. If your screening comes back normal, no other tests are necessary.
Glucose tolerance test
This test diagnoses gestational diabetes. It takes three hours to complete and involves drawing your blood several times at specific intervals. The test is more involved and requires you to fast (no eating or drinking for several hours before the test). The glucose tolerance test is sometimes called a three-hour glucose test.
When is a glucose challenge test performed during pregnancy?
Screening for gestational diabetes usually occurs around weeks 24 to 28 of pregnancy. Your provider may perform testing sooner if you:
- Had diabetes in a prior pregnancy.
- Have sugar in your pee during a prenatal visit.
- Have a family history of diabetes.
- Have obesity.
- Have high blood pressure.
- Are older than 35.
- Have a condition like PCOS (polycystic ovary syndrome) or another condition associated with an increased risk for diabetes.
How do I prepare for my one-hour glucose test?
You don’t need to prepare for your one-hour glucose screening. Most pregnancy care providers recommend avoiding foods high in sugar for breakfast. For example, pancakes, donuts or juice. If you’re testing later in the day, be aware that eating large amounts of sugar for lunch may affect your results.
Can you eat before a glucose screening test?
Yes, you can eat normally before your glucose screening test.
What can I expect on the day of the glucose screening?
On the day of your glucose screening, follow instructions given to you by your prenatal care provider or the lab (if applicable). Be sure to know exactly where to go for the screening and if you need an appointment.
How is a glucose screening performed during pregnancy?
A glucose screening test involves quickly (within five minutes) drinking a sweetened liquid (called glucola), which contains 50 grams (g) of glucose, a type of sugar. A phlebotomist takes a blood sample from a vein in your arm 60 minutes (one hour) after drinking the solution. The blood test measures how the glucose solution was processed by your body. You can’t eat or drink anything from the time you drink glucola until after your blood draw. Having a few sips of water is usually OK.
A higher-than-normal blood glucose level after 60 minutes doesn’t mean you have gestational diabetes. It means your provider will order a second glucose test (glucose tolerance test) to diagnose gestational diabetes.
How do I prepare for a glucose tolerance test?
If you fail your glucose screening, your pregnancy care provider will suggest a second test to diagnose gestational diabetes. This test is similar, but lasts longer and requires more blood draws.
Your pregnancy care provider will give you specific eating instructions before your test. The instructions may include:
- Eating at least 150 milligrams (mg) of carbohydrates per day for three days before testing.
- Restricting all food and drink for at least eight to 12 hours before the test. Drinking a few sips of water the morning of the test is usually OK.
- Scheduling your test for first thing in the morning.
It’s important to note, it’s possible to fail your glucose screening but pass a glucose tolerance test.
How is the glucose tolerance test performed during pregnancy?
Unlike the glucose screening test, drinking the sugary solution isn’t the first step in a three-hour glucose tolerance test. First, a phlebotomist will take your fasting blood glucose level. This is your blood sugar level on a completely empty stomach.
Then, you’ll quickly (within five minutes) drink a sweetened liquid (glucola) containing 100 grams of glucose. You’ll have your blood drawn after one, two and three hours from the time you finished your drink.
You’re not permitted to leave while you wait for your next blood draw. Bring a book, magazine or other entertainment to occupy yourself. Most providers allow you to have sips of water during the testing period. However, you aren’t permitted to eat anything until after your last blood draw.
How long does the glucose test take?
The glucose screening takes a little over an hour. The glucose tolerance test takes over three hours.
Can I drink water during the glucose tolerance test?
Most providers allow sips of water during the three-hour glucose test. Check with your provider’s office to be sure.
Are there any side effects of the sugar drink during the test?
Most people don’t have any side effects from the drink. Some people say it makes them feel nauseated or dizzy, but serious side effects are rare. The glucose drink tastes like extra sweet Gatorade® or flat soda, which may be unpleasant.
Results and Follow-Up
How long does it take to get the results of a gestational diabetes screening?
Most people know the results of their gestational diabetes screening within one or two days. Check with your provider to see when you can expect your results.
What is the normal range for a one-hour glucose test?
Blood sugar values lower than 140 milligrams (mg) per deciliter (dL) are normal. You don’t need additional testing for gestational diabetes.
If your blood sugar value is 140 mg/dL or higher, your provider will recommend the three-hour glucose tolerance test.
Please note that all providers are different and normal ranges may vary. For example, some providers consider anything higher than 135 mg/dL to be abnormal.
What is the normal range for a three-hour glucose test during pregnancy?
For a three-hour glucose tolerance test:
- Fasting blood sugar levels should be lower than 95 mg/dL.
- After one hour, blood sugar levels should be lower than 180 mg/dL.
- After two hours, blood sugar levels should be lower than 155 mg/dL.
- After three hours, blood sugar levels should be lower than 140 mg/dL.
Keep in mind, your provider may have a slightly different normal range. Generally speaking, if your blood sugar is elevated in at least two of your results, your provider will diagnose you with gestational diabetes. If you have one elevated result, your provider may ask to test you again in a few weeks.
Make sure you understand the results of your glucose test and discuss any concerns you have with your provider.
What happens if I fail my three-hour glucose test?
If you fail your three-hour glucose test, your provider will diagnose you with gestational diabetes. Treating diabetes during pregnancy typically involves making modifications to your diet and using a blood glucose meter to measure your blood sugar at specific times during the day. A blood glucose meter is a machine that uses a drop of your blood to give you a blood sugar reading. If diet changes alone don’t help, you may need insulin to manage gestational diabetes. Your pregnancy care provider or a dietician will help you manage your blood glucose level for the rest of your pregnancy.
Can I refuse the glucose challenge test when pregnant?
Yes, you can refuse the glucose screening. However, most major medical associations and pregnancy care providers recommend all pregnant people be screened for gestational diabetes. Glucose screenings are the only way to help your provider diagnose gestational diabetes. Gestational diabetes puts you and the fetus at risk for complications.
Why do you need a glucose test during pregnancy?
A glucose test helps your pregnancy care provider diagnose gestational diabetes. If you have diabetes during pregnancy, managing your blood sugar level is important. If left untreated, diabetes can cause serious complications. Some of the complications are:
- Preeclampsia (a type of high blood pressure during pregnancy).
- Delivering a large baby, which increases your risk of birth injuries or C-section.
- Low blood sugar for your baby after they’re born (hypoglycemia).
- Your baby’s at higher risk for Type 2 diabetes later in life.
How do you pass your pregnancy glucose test?
How your body works to process glucose during pregnancy is mostly out of your control. However, eating sugary, sweet foods before your screening will affect your results. These include things like bread, pasta, cakes, sugary cereals, juices and soft drinks. If you want to pass your glucose screening test, avoid these foods and drinks prior to the test.
A note from Cleveland Clinic
Screening for gestational diabetes is just one of the many tests you’ll have during pregnancy. It’s become a routine part of prenatal care because unmanaged diabetes can cause complications for both you and the fetus. Glucose tests are simple and relatively painless. It involves drinking a sweet, sugary liquid and getting blood drawn from a vein in your arm at specific intervals. If your body isn’t processing glucose correctly, your blood glucose levels will be elevated or abnormal. Talk to your pregnancy care provider to make sure you understand what a glucose test is, when to get it and where you need to go. They can help you understand the process.
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