What to Expect From Gestational Diabetes Testing

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Gestational diabetes, or diabetes that develops during pregnancy, is a relatively common condition. Between 2% and 10% of all pregnancies are affected by gestational diabetes, according to the Centers for Disease Control and Prevention (CDC). 

“We know that if we diagnose and treat gestational diabetes, we can significantly improve your health and your baby’s health,” says Amy Banulis, MD, an OB/GYN for Kaiser Permanente in Falls Church, Virginia. “Untreated gestational diabetes has been associated with a whole host of complications for both mom and baby.” 

The only way to know for sure if you have this condition, however, is to undergo blood sugar, or blood glucose testing during your pregnancy. Here’s what you need to know about this routine, but critical, test during pregnancy. 

Purpose of Glucose Testing During Pregnancy

When you're pregnant, your body often develops some insulin resistance, so you need even more insulin to help your body use sugar for energy. Without blood glucose testing, you might never know you have gestational diabetes.

Gestational diabetes is largely asymptomatic. Even if you do have symptoms, they’re likely to be mild and can be easily mistaken for other traits associated with pregnancy, like increased thirst or an increased need to urinate. While there are some risk factors that increase the likelihood that you’ll develop gestational diabetes, many people develop it without having any risk factors at all. 

As a result, blood glucose testing is really the only way for your doctor to identify this condition and make a diagnosis. That’s key because if you do have gestational diabetes, you need to begin treatment to reduce your chances of experiencing complications. 

Button Smith, a school librarian in Birmingham, Alabama, remembers being shocked when her glucose tolerance test revealed sky-high blood sugar levels during her pregnancy. “Nobody in my family had ever had it, so it was odd and new to me,” says Smith, whose daughter is almost 11 years old. 

Types of Glucose Tests Given During Pregnancy

There are two different types of blood glucose tests given to pregnant people. Here's what you need to know about each, including when you might have to take one or the other.

One-Hour Oral Glucose Screening Test

All pregnant people undergo a one-hour glucose screening test, unless they already have diabetes when they became pregnant. 

Typically, your healthcare provider will schedule the test between your 24th and 28th week of pregnancy. However, if you’re at elevated risk, your doctor might schedule the test earlier. 

When you go for your test, you will drink 50 grams of a very sugary drink. You may have heard some people complain about just how sweet it is, but it’s necessary to see how your body responds to the sugar.

“The first thing I tell people is that it’s not as bad as people say,” says Salena Zanotti, MD, an OB/GYN with the Cleveland Clinic. “People get so nervous about it.”

Darby McKenzie, a College Station, Texas, mother of a toddler, with another baby on the way, jokes about her experience. “I completed the test and tried the orange-flavored drink for the first time," she recalls. "Eight out of ten for flavor. Negative eight out of ten for enjoyment.”

Usually providers keep the drinks refrigerated so they’ll go down a little easier. Dr. Zanotti says her facility offers the glucose drink in several different flavors, so you might ask if you can choose a particular flavor. 

One hour after you finish the drink, you’ll get your blood drawn. If your blood glucose level falls below 140 mg/dL, you’re in the clear. But if the test reveals a glucose level of 140 mg/dL or higher, you’ll need to undergo the next level of testing: the three-hour oral glucose tolerance test. 

Three-Hour Glucose Tolerance Test

The three-hour glucose tolerance test will help your doctor confirm or rule out gestational diabetes. This test requires fasting in advance and four different blood draws.

First, you’ll arrive at your doctor’s office or lab and get your blood drawn to establish your fasting blood sugar level. Next, you’ll down another sugary drink, except this time, you have to drink 100 grams, not just 50 grams. Then you’ll get your blood drawn three more times at one-hour intervals so your glucose can be measured each time.

If you have two or more high blood glucose readings at any point in this process, your doctor may tell you that you have gestational diabetes.

Abnormal readings for each section of the test are:

  • Fasting: 95 mg/dL or higher
  • One hour: 180 mg/dL or higher
  • Two hours: 155 mg/dL or higher
  • Three hours: 140 mg/dL or higher

How to Prepare for Glucose Testing

You don’t have to do anything special to prepare for the one-hour test. “Patients do not have to be fasting,” says Dr. Zanotti. “That’s another myth that’s out there: that they have to fast.” 

Dr. Banulis does usually recommends her patients eat a healthy breakfast before they come in—and try to avoid eating anything that’s really high in carbs or sugar.

However, the three-hour test is a different story. You do need to fast for at least eight hours prior. Most doctors recommend fasting overnight, with an appointment at your doctor’s office or lab first thing in the morning. “Bring something to do to keep yourself distracted or occupied while you wait,” suggests Dr. Banulis.

Gestational Diabetes Follow Up

Once you know you have gestational diabetes, you’ll learn how to take care of yourself and manage your blood sugar levels for the remainder of your pregnancy. Don’t worry, you won’t have to figure it out on your own. Doctors, nurses, diabetes educators, and registered dietitians work with patients to help them navigate everything. 

“In our practice, you would come in as soon as possible to get started on a diet and monitoring of your blood sugar levels at home with a glucometer," adds Dr. Banulis.

After consulting with a dietitian and learning more about managing, Smith was able to control her gestational diabetes with her diet. She dutifully checked her blood sugar levels and made sure she always had access to the right kind of food. There were times when it was hard to say no to pasta—a challenge in her Italian family–but she made it work. 

“I made up my mind that I was going to do it, and I did,” Smith says.

A Word From Verywell

You could think of glucose testing during pregnancy as a necessary evil. You probably won’t enjoy it, but it’s important for your health—and the health of your baby—to know if you have gestational diabetes. If you know what to expect with a glucose tolerance test, it may help ease some anxiety around it. While a gestational diabetes diagnosis may be scary, there are plenty of people and resources to help you manage it. Make sure to reach out to your healthcare provider with any questions about the test or gestational diabetes.

7 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Centers for Disease Control and Prevention. Gestational Diabetes.

  2. National Institute of Diabetes and Digestive and Kidney Diseases. Symptoms & Causes of Gestational Diabetes.

  3. Centers for Disease Control and Prevention. Diabetes Risk Factors.

  4. National Institute of Diabetes and Digestive and Kidney Diseases. Tests & Diagnosis for Gestational Diabetes.

  5. Centers for Disease Control and Prevention. Diabetes Tests.

  6. UpToDate. ACOG two-step approach for screening and diagnosis of gestational diabetes mellitus.

  7. National Institute of Diabetes and Digestive and Kidney Diseases. Managing & Treating Gestational Diabetes.

Additional Reading

By Jennifer Larson
Jennifer Larson is a seasoned journalist who regularly writes about hard-hitting issues like Covid-19 and the nation's ongoing mental health crisis, as well as healthy lifestyle issues like nutrition and exercise. She has more than 20 years' of professional experience and hopes to log many more.