The standard glucose screening test used during pregnancy contains 50 grams of sugar, roughly the same amount found in a 20-ounce bottle of soda. If that initial screen flags a potential issue, the follow-up diagnostic test contains either 75 or 100 grams of sugar, depending on which testing method your provider uses.
The One-Hour Screening Test: 50 Grams
The first glucose test most people encounter is a quick screening, typically done between 24 and 28 weeks of pregnancy. You drink a sweet syrup containing 50 grams of sugar, then have your blood drawn one hour later. You don’t need to fast beforehand.
The sugar in the drink is dextrose, a simple form of glucose derived from corn syrup. The most common brand, Glucola, comes in an orange-flavored version (which contains orange food coloring) and a lemon-lime version without added dye. The drink also contains purified water and the preservative sodium benzoate. Many people describe it as tasting like a flat, overly sweet soda or melted popsicle.
A blood sugar reading below 140 mg/dL after one hour is considered normal. Some clinics use a lower cutoff of 130 mg/dL. If your result falls between 140 and 190 mg/dL, you’ll be asked to come back for the longer diagnostic test. A result of 190 mg/dL or higher typically means gestational diabetes can be diagnosed from the screening alone, without a follow-up.
The Three-Hour Diagnostic Test: 100 Grams
If your one-hour screen comes back elevated, the next step is a three-hour glucose tolerance test that uses 100 grams of sugar, double the amount in the screening drink. This one requires fasting overnight beforehand. Your blood is drawn four times: once fasting, then at one, two, and three hours after finishing the drink.
Each blood draw has its own threshold:
- Fasting: 95 mg/dL or lower
- One hour: 180 mg/dL or lower
- Two hours: 155 mg/dL or lower
- Three hours: 140 mg/dL or lower
Two or more readings above these cutoffs result in a gestational diabetes diagnosis. If only one value is elevated, your provider may recommend monitoring or retesting later in pregnancy.
The 75-Gram Alternative
Some providers use a one-step approach that skips the initial 50-gram screening entirely. Instead, you go straight to a 75-gram glucose tolerance test with blood draws at fasting, one hour, and two hours. This method is more common outside the United States and is recommended by the World Health Organization.
ACOG (the American College of Obstetricians and Gynecologists) still recommends the two-step approach for most practices: 50-gram screen first, then the 100-gram diagnostic test if needed. However, ACOG notes that individual practices may choose the 75-gram one-step test if it better suits the population they serve.
How Much Sugar That Actually Is
For context, 50 grams of sugar is about 12 teaspoons. A standard can of Coca-Cola has 39 grams. So the screening drink packs roughly 25% more sugar than a can of Coke, and you’re expected to finish it within about five minutes. The 100-gram version contains the sugar equivalent of about two and a half cans of soda, consumed on an empty stomach. This is why many people feel nauseous, jittery, or lightheaded during the test, especially the three-hour version.
Dosing for Children
When children need a glucose tolerance test (often for conditions like cystic fibrosis or suspected type 2 diabetes), the dose is based on body weight: 1.75 grams of glucose per kilogram, up to a maximum of 75 grams. A 40-pound child, for example, would drink about 32 grams rather than the full adult dose.
Researchers have also studied alternatives to the standard glucose drink for children, including dextrose-based candy and jellybeans, since the syrupy drink can be harder for kids to tolerate. These aren’t yet standard practice, but some pediatric centers offer them.
Preparing for the Test
The one-hour, 50-gram screening requires no fasting and no special preparation. You can eat normally before your appointment.
The longer diagnostic tests (75-gram or 100-gram) require an overnight fast of at least 8 hours. In the days leading up to these tests, guidelines from the International Workshop-Conference on Gestational Diabetes recommend eating a moderate to high-carbohydrate diet for three days beforehand. Restricting carbs before the test can skew your results, potentially causing a false positive. Eating normally, with plenty of grains, fruits, and starchy vegetables in the days before, gives the most accurate reading of how your body actually handles sugar.