When I was pregnant with my first child, a few of my close friends happened to be expecting at the same time. This was a huge stroke of unplanned luck—the messages we sent each other throughout the months and during middle-of-the-night wake-ups with newborns could fill a highly entertaining, if slightly overwrought, book. But it also showed the differences in the information we had and the actions we took.
Case in point: I distinctly remember eating my regular breakfast before my one-hour gestational diabetes screening—known officially as the glucose challenge test or glucose screening test—while a friend fasted ahead of hers.
Though I didn’t think much of it at the time—I wasn’t sure if her doctor had given her any particular or personal reason for doing so—since then, some friends have said they fasted and others have said they didn’t, making it clear that there is some confusion on what to do. So, I set out to set the record straight and figure out the definitive answer to what you should eat before your gestational diabetes test. Before I dive into everything you need to know, first a cheat sheet.
Your Gestational Diabetes Screening Cheat Sheet:
The one-hour test: It’s important to eat normally before this test so your doctor can get an accurate reading.
The three-hour test: Make sure to eat as you normally would for the three days before the test. Then, fast for 8-10 hours before the test, only taking sips of water as needed.
Why Is Gestational Diabetes Screening Important?
First, a quick recap on gestational diabetes itself. The condition, which impacts about 6 in 100 expectant moms, according to the March of Dimes1 , is indicated by high levels of sugar, or glucose, in your blood.
“All mothers who are pregnant have a risk of developing gestational diabetes,” says Abdulla Al Khan, MD, the vice chairman of the ob-gyn department and director of Maternal-Fetal Medicine and Surgery at Hackensack University Medical Center.
That’s because, when you’re pregnant, your body is producing a whole slew of hormones, including estrogen, progesterone, and HPL (human placental lactogen), which have insulin-blocking receptors, says Dr. Al Khan. “When insulin receptors are blocked, glucose cannot readily be uptaken by the cell, hence the mother’s glucose levels can be elevated transiently.”
As Dr. Al Khan notes, “If you’re pregnant, by definition, your body is producing all of these hormones, which can lead to the development of gestational diabetes.”
At play may also be other individual factors—such as being overweight or obese, high blood pressure, or having dealt with the condition before—that could also increase your chances of developing gestational diabetes.
Knowing whether you have gestational diabetes or not is important. If you do develop the condition and it’s not controlled properly, you may end up dealing with a variety of potentially dangerous issues, including delivering a baby that’s either very large—which ups the possibility for things like birth injuries—or having a small, growth-restricted baby, says Dr. Al Khan. When left untreated, it could also put you at risk of having diabetes in the future, among other issues.
This is where screening comes in. According to Dr. Al Khan, screening all moms for gestational diabetes has had a huge impact on reducing the risks and potential negative outcomes of the condition.
What to Eat Before the One-Hour Gestational Diabetes Test
So, how does screening work? Typically, at some point between week 24 and week 28 of pregnancy, you’ll go through a one-hour glucose challenge test.
For this test, you’ll down a concentrated glucose drink (you’ve probably heard about this sweet beverage, which tastes vaguely of soda). Then, an hour later, the nurse will draw your blood to test your glucose levels.
Prep for this test is easy: eat normally. “The last thing you want to do is modify your diet,” says Dr. Al Khan. “I always tell my patients, ‘Don’t be conservative in terms of what you’re eating because the last thing I want to do is get a false negative.’”
Along those same lines, the test can happen at any time of day—morning or afternoon—and the same rule applies: don’t change up or modify your diet.
When your results come back, if your blood sugar levels are under 140, you’re typically done with screening for the rest of your pregnancy. “Anything greater than 140 is considered an abnormal test,” says Dr. Al Khan. He also notes that this number is just the standard, and that, depending on your own risk factors, your provider might lower the threshold to 135 or 130, in order to make sure they’re not missing any cases of the condition.
What to Eat Before the Three-Hour Gestational Diabetes Test
Should the one-hour test indicate that your sugar levels are high, you’ll then do what’s known as the Oral Glucose Tolerance Test, which lasts three hours.
As Dr. Al Khan explains, “With the three-hour, once again, it is still considered a screening test, but it is a screening test with a higher sensitivity and higher specificity.”
With this test, you’ll go to your provider’s office, where they’ll do a blood draw to determine your fasting glucose level, says Dr. Al Khan. From there, you’ll drink the glucose drink—this time around, you’ll be given the big gulp version of it—and then have your blood drawn again at the one, two, and three-hour marks.
When it comes to what to eat, there are two important points to know. The first? You have to fast for 8 to 10 hours before the actual test, so your fasting glucose levels can be measured. This is typically an overnight fast and the test is done first thing in the morning, says Dr. Al Khan.
So if your test is at 8 am, Dr. Khan recommends not eating after 10 pm. You can drink water but avoid other beverages, like juice.
Along with not eating, you also shouldn’t do any strenuous activity—so no 5 am spin class that day—and don’t smoke, which of course you shouldn’t be doing anyway, he says.
The other important thing to note: In the days leading up to your fast—particularly in the three days prior—eat the way you normally would and don’t change your diet. The reasoning is the same as with the one-hour test: If you restrict your diet—for example, if you really limit your carbs—you may end up with a false negative. In other words, you could still have gestational diabetes, but the screening will have missed it. And ultimately, as Dr. Al Khan explains, this could put yourself and your baby at risk.
If your glucose levels are high with this test, then you’ll be treated and managed for gestational diabetes, which may include things like diet/lifestyle changes or taking medications.
What Happens If You’re High Risk?
While what you eat before either screening doesn’t change if you are at high risk, what might change is when your doctor administers the test. For example, your provider may recommend doing early screening for gestational diabetes or even repeating it later on in your pregnancy, since gestational diabetes can develop at any point, notes Dr. Al Khan.
He stresses the importance of individualized care like this. For instance, if a patient is at a very high risk, he says he may turn straight to having them check their blood sugar levels with a glucose monitor or finger-prick/test strip, for instance. This way, if levels are high, treatment isn’t delayed, he says.
While all of this may sound a little scary, the most important thing to remember is that this is one pregnancy condition that can be treated and managed—which is also why good communication with your provider is important. If you do develop gestational diabetes, your doctor will work with you to address the condition so you and your baby will be just fine.
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