The 1-Hour Glucose Test in Pregnancy: What Happens and Whether You Can Prep for It
The 1-hour glucose test in pregnancy comes at 24 to 28 weeks. What the drink does, why screening positive usually isn't a diagnosis, and how to prep.
Somewhere around 24 weeks, a nurse hands you a small bottle of syrupy orange liquid and tells you to finish it in five minutes. Then you sit in the waiting room for an hour, get your blood drawn, and go home wondering what you just did.
That’s the 1-hour glucose test in pregnancy, and the thing nobody explains clearly in the two minutes before you drink it: this is a screen, not a diagnosis. A high number doesn’t mean you have gestational diabetes. It means the screen flagged you for the real test.
When it happens and why
Most US practices screen between 24 and 28 weeks. That timing isn’t arbitrary. The placenta ramps up hormone production in the second half of pregnancy, and those hormones make your cells less responsive to insulin. Your pancreas is supposed to compensate by making more.
Gestational diabetes is what happens when it can’t keep up. Weeks 24 through 28 are when the strain first shows in a blood sugar reading.
Some people get screened at their first prenatal visit too, then again in the usual window. ACOG’s criteria for that early screen are a BMI of 25 or higher (23 or higher if you’re Asian American) plus at least one other risk factor: a prior pregnancy with gestational diabetes, a first-degree relative with type 2 diabetes, PCOS, a previous baby weighing 8 lb 13 oz or more, high blood pressure, or an A1C of 5.7 percent or higher. Early screening is a wider net, nothing more.
Not sure when your window lands? Our due date calculator will tell you what week you’ll be in on a given date.
What the drink actually is
Fifty grams of glucose in water, usually flavored orange, fruit punch, or lemon-lime. It tastes like flat soda someone made twice as strong.
Most people get through it fine. Some feel queasy or shaky in the first half hour, which is a normal response to a fast sugar load and passes.
You generally don’t need to fast for this one. Eat a normal breakfast, skip the cinnamon roll. A few practices ask you to fast anyway, so call and confirm. Once you drink it, the clock starts. Don’t wander off; the draw has to happen at 60 minutes for the number to mean anything.
Ask whether your practice offers an alternative to the standard drink. Some allow a dye-free glucose beverage, which is the same 50-gram load without the coloring. Jelly bean protocols held up in a small randomized trial with fewer side effects, but no national guideline endorses them. Ask; don’t assume.
Screening positive is common and usually isn’t gestational diabetes
Your practice sets a cutoff and applies it to everyone. ACOG says to pick a single consistent threshold, either 135 or 140 mg/dL; some practices use a lower 130 instead. A lower cutoff catches more cases and also sends more people to the next test unnecessarily.
Depending on the threshold, somewhere around 15 to 20 percent of people screen positive, and fewer than one in five of those go on to be diagnosed. Gestational diabetes shows up in roughly 8 percent of US pregnancies. So if you get the call, the odds are still in your favor. A text saying “your glucose was elevated, we’re scheduling the three-hour” is not a diagnosis and shouldn’t be read as one.
The three-hour test is the real one
This test is longer and stricter. You fast for 8 to 12 hours overnight, get a baseline blood draw, drink 100 grams of glucose, then get drawn again at one, two, and three hours. Four sticks total. You can’t eat, and don’t go for a walk to pass the time; activity changes your numbers.
Common thresholds (Carpenter-Coustan) are 95 fasting, 180 at one hour, 155 at two hours, and 140 at three hours. You need two or more values at or above those to be diagnosed. ACOG is clear that a single high value isn’t enough, though some practices will watch you more closely after one.
Bring a phone charger, a book, and food for the drive home. Three hours in a lab waiting room while fasting and pregnant is a long morning.
Some practices skip the two-step approach and use a one-step 75-gram fasting test, where a single elevated value diagnoses. Both are accepted, though ACOG still supports two-step as its default. Ask which your office uses before you show up.
Can you prepare for it?
Not really, and you shouldn’t try to game it.
Cutting carbs for a week beforehand doesn’t help. Outside pregnancy, standard practice is to eat at least 150 grams of carbohydrate a day for three days before a glucose tolerance test, because carb restriction blunts your insulin response. The pregnancy-specific data is thinner, but the direction of the effect isn’t in your favor. Loading up on sugar the morning of skews things the other way. This isn’t a grade. The number only helps your provider if it reflects how your body actually handles glucose.
What’s reasonable: eat normally in the days before, don’t have a huge sugary breakfast that morning, get a decent night’s sleep, and book a time you won’t be rushing to. If you have a history of fainting during blood draws, say so at check-in.
If you are diagnosed
Most people with gestational diabetes manage it with food changes, walking after meals, and finger-stick monitoring four times a day. Roughly 80 percent get there without medication. The rest need insulin or metformin, and that’s not a personal failure. Placental hormones drive this. Willpower has very little to do with it.
The upside of catching it is real. Two large randomized trials found that treating gestational diabetes lowered rates of pre-eclampsia and gestational hypertension and cut the odds of an oversized baby. You’ll likely get extra growth ultrasounds and more frequent third-trimester visits, which is also around when your provider may ask you to start tracking movement. Our kick counter is there for that.
One thing that gets forgotten in the newborn haze: ACOG recommends a follow-up glucose test 4 to 12 weeks after you deliver, because about half of people who’ve had gestational diabetes go on to develop type 2 diabetes. Put the appointment in your phone now.
More second and third trimester guides are in our pregnancy section.
This article is general information, not medical advice. Screening protocols and cutoffs vary between practices. Talk to your OB or midwife about which test you’re getting and what your results mean, and see current ACOG and CDC guidance for details.