How Much Sugar Is in the 3-Hour Glucose Drink?

The glucose drink used for the 3-hour oral glucose tolerance test contains 100 grams of pure glucose, which is roughly equivalent to 25 teaspoons of table sugar dissolved in about 10 ounces of liquid. That is nearly twice what you drink during the initial 1-hour screening, which uses 50 grams. The amount is deliberately high and standardized so that your body’s insulin response can be measured under a controlled, reproducible sugar load.

What 100 Grams of Glucose Actually Looks Like

If you have ever tried to picture 100 grams of sugar, think of it as roughly the amount in two and a half cans of regular soda, except you are drinking it all in a concentrated solution within about five minutes. The beverage itself, often sold under brand names like Glucola or SunDex, comes in a small bottle that is intensely sweet. Most formulations are flavored with orange, lemon-lime, or fruit punch to make the experience somewhat more palatable, but the overwhelming sweetness is hard to mask when the sugar concentration is that high.

The drink is not the same thing as a sugary soda or juice, though. It contains pharmaceutical-grade glucose, which is a simple sugar that enters your bloodstream faster than the mix of sugars you would get from a soft drink. Sucrose (table sugar) has to be broken down into glucose and fructose before it can be absorbed, and high-fructose corn syrup adds another wrinkle. The test uses pure glucose specifically because it produces a sharp, predictable blood sugar spike that clinicians can measure at exact time intervals.

Why the 3-Hour Test Exists and How It Differs From the 1-Hour Screen

Most pregnant people first encounter glucose testing around 24 to 28 weeks of pregnancy with the 1-hour screening test, which uses 50 grams of glucose. That test is not a diagnosis on its own. If your blood sugar at the one-hour mark is above the threshold your provider uses (typically around 130 to 140 mg/dL), you get sent for the longer, more definitive 3-hour version. This two-step approach, endorsed by the American College of Obstetricians and Gynecologists, has been the standard screening strategy in the United States for decades.¹

The 3-hour test requires overnight fasting, which the 1-hour screening does not. After a fasting blood draw, you drink the full 100 grams of glucose, and then your blood is drawn again at one hour, two hours, and three hours. That gives your provider four glucose values. If two or more of those values exceed the diagnostic cutoffs, gestational diabetes is diagnosed.

There is also a separate one-step approach that uses 75 grams of glucose in a 2-hour test. This was recommended by the International Association of Diabetes and Pregnancy Study Groups (IADPSG) based on a large international study. Different providers use different approaches, and the choice between the two has been the subject of ongoing clinical debate, which we will get to shortly.

The Diagnostic Cutoffs and What They Mean

Two sets of diagnostic criteria are widely used for the 100-gram, 3-hour test. The Carpenter-Coustan criteria set lower thresholds, while the National Diabetes Data Group (NDDG) criteria are more conservative. Under Carpenter-Coustan, the cutoffs are: fasting 95 mg/dL, one-hour 180 mg/dL, two-hour 155 mg/dL, and three-hour 140 mg/dL. Under NDDG, those numbers are higher: fasting 105, one-hour 190, two-hour 165, and three-hour 145. A diagnosis requires meeting or exceeding at least two of the four values.²

Which set of cutoffs your provider uses matters quite a bit, because the Carpenter-Coustan criteria capture more borderline cases. The difference is not trivial for the person being tested. If your one-hour reading comes in at 185 mg/dL, for example, that is abnormal under Carpenter-Coustan but normal under NDDG. Whether that result counts toward a gestational diabetes diagnosis depends entirely on which framework your hospital follows.

What Happens When Only One Value Is Abnormal

A question that causes real anxiety for many pregnant people is what it means when just one of the four values comes back high. Technically, one abnormal value does not meet the diagnostic criteria for gestational diabetes under either set of guidelines. But that does not mean it is clinically meaningless. A systematic review and meta-analysis found that patients with a single abnormal glucose value had meaningfully higher rates of complications compared with those who had all normal values. Those complications included larger-than-average babies, a higher rate of cesarean delivery, and higher rates of pregnancy-related high blood pressure.³

This creates a gray zone that different providers handle differently. Some will treat one abnormal value with dietary monitoring and lifestyle changes even though it does not technically qualify as gestational diabetes. Others will reassure you that the test was normal and move on. If you fall into this category, it is worth asking your provider directly what their approach is, because the evidence suggests that a single elevated reading is not the same as a clean bill of health.

Side Effects of Drinking That Much Sugar at Once

Nausea is the side effect that dominates online discussions, and for good reason. Drinking 100 grams of glucose on an empty stomach can trigger nausea, dizziness, headache, and occasionally vomiting. Vomiting is particularly problematic because if it happens before your blood draws are complete, the test may need to be repeated. A randomized trial tested whether changing the water temperature or adding flavorings to the glucose solution could reduce side effects. The formula adjustments improved how the drink tasted and reduced nausea somewhat, but did not eliminate vomiting, headache, or bloating.⁴

In certain populations, the side effects are dramatically worse. A study of post-bariatric surgery patients who underwent an oral glucose tolerance test found that nearly two-thirds experienced adverse effects. Common complaints included nausea in about 38% of participants, dizziness in about 31%, weakness in about 26%, and diarrhea in about 23%. More concerning, roughly 15% experienced low blood sugar (hypoglycemia) during the test, and one patient’s glucose dropped to a dangerously low 24 mg/dL.⁵ Those numbers come from a specific group with altered digestive anatomy, so they do not represent the typical pregnant person’s experience. But if you have had bariatric surgery and are facing a glucose tolerance test during pregnancy, your provider needs to know, because the rapid sugar dump into your altered digestive system can cause a severe reaction.

Does What You Eat Before the Test Change Your Results?

You will often hear advice to “carb-load” in the days leading up to the 3-hour test, eating extra pasta, bread, and rice to prime your body to handle the glucose drink. This advice has been around for decades, rooted in older research suggesting that a low-carbohydrate diet could artificially impair glucose tolerance and produce a false positive. A randomized study specifically testing this in healthy pregnant women found no significant difference in glucose values between those who followed a preparatory high-carbohydrate diet and those who did not, and concluded that the diet unnecessarily delays diagnosis.⁶

That said, the concern about low-carbohydrate eating is not entirely baseless. A case report and review argued that if someone has been following a very low-carb or ketogenic diet and then takes the test without adjusting their eating, the sudden glucose load can provoke an exaggerated blood sugar spike because the body is not accustomed to processing large amounts of carbohydrate. The recommendation is not necessarily a multi-day carb-loading protocol, but rather that patients and providers should communicate clearly about dietary patterns before the test to avoid false positives.⁷

The practical takeaway is this: if you eat a normal, mixed diet, you probably do not need to do anything special in the days before the test. If you have been eating very low-carb, mention it to your provider. And regardless of your usual diet, the overnight fast before the 3-hour test is non-negotiable for accurate results.

Alternatives to the Standard Glucose Drink

Given how unpleasant many people find the glucose solution, there has been long-standing interest in replacing it with something more tolerable. The most studied alternative is jelly beans. Two separate trials evaluated whether eating jelly beans containing the equivalent amount of sugar could serve as a stand-in for the standard beverage during the 50-gram screening test. One study of 136 participants found no significant difference in one-hour glucose values, sensitivity, or specificity between jelly beans and the standard drink.⁸ An earlier trial also found comparable diagnostic performance and reported that patients tolerated the jelly beans better.⁹

These studies are encouraging but limited. Both tested the 50-gram screening step, not the full 100-gram diagnostic test. Eating 100 grams worth of jelly beans in one sitting presents its own practical challenges, and no large trial has validated that approach for the 3-hour test. Most providers still require the standardized glucose solution for the diagnostic test because the absorption rate is more predictable and reproducible.

Continuous glucose monitoring (CGM) represents a more futuristic alternative. A feasibility study explored whether pregnant women could wear a small sensor on their arm and complete a glucose challenge at home rather than sitting in a clinic for three hours. Most participants completed the home-based test, and feedback was overwhelmingly positive, with all 20 women interviewed saying they would recommend it to others.¹⁰ This is still early-stage research, though, and CGM has not yet replaced the oral glucose tolerance test in clinical practice for gestational diabetes diagnosis.

The One-Step Versus Two-Step Debate

If you have done any reading about gestational diabetes testing, you have probably encountered conflicting advice about whether your provider should use the two-step method (50-gram screen followed by the 100-gram, 3-hour test) or the one-step method (a single 75-gram, 2-hour test with no preliminary screen). This debate has been going on for years and remains unresolved.

The one-step approach, promoted by the IADPSG, diagnoses substantially more women with gestational diabetes. A large randomized trial found that 16.5% of women screened with the one-step method were diagnosed with gestational diabetes, compared with 8.5% using the two-step method.¹¹ A review of multiple studies estimated that adopting the IADPSG criteria increases the prevalence of gestational diabetes diagnoses by roughly one to nearly four times compared with whatever baseline criteria a facility was previously using.¹²

Whether diagnosing more women is a net positive or a net negative is where opinions diverge. Proponents argue that catching milder cases allows for early intervention that prevents complications. Critics worry about medicalizing pregnancies that would have been fine without intervention, adding stress, costs, and unnecessary monitoring. For the person sitting in a waiting room wondering how much sugar is in the drink they are about to consume, the practical consequence is this: the 3-hour test with 100 grams of glucose is what you will face under the two-step system used by most U.S. providers. If your practice uses the one-step approach instead, you will drink 75 grams and be done in two hours.

How the Sugar Amount Compares Across Test Versions

To keep the numbers straight, here are the glucose loads for the different tests you might encounter during pregnancy:

50-gram GCT: The initial screening test. No fasting required. One blood draw at one hour. This is not diagnostic on its own.
75-gram OGTT: Used in the one-step approach. Requires fasting. Blood drawn fasting, at one hour, and at two hours. Three values total.
100-gram OGTT: The 3-hour diagnostic test used in the two-step approach. Requires fasting. Blood drawn fasting, at one hour, two hours, and three hours. Four values total.

The 100-gram test is the longest, the most sugar-intensive, and the one that tends to produce the worst side effects, simply because there is more glucose hitting your system. It is also the only version that requires you to sit in a lab or clinic for three full hours between blood draws, which adds discomfort and boredom to an already unpleasant experience.

Tips That Actually Help on Test Day

There is no trick that will change your test results if you genuinely have gestational diabetes, and you should not want there to be. An accurate diagnosis protects you and your baby. But there are a few things that can make the experience less miserable without compromising the test.

Drink the solution cold. Cold beverages mask sweetness, and while the evidence on specific temperature effects is modest, the randomized trial on glucose drink formulations found that taste perception was significantly better with certain preparations, even when clinical outcomes stayed the same.⁴ Ask your provider’s office whether they keep the drinks refrigerated, or whether you can pick up the bottle ahead of time and chill it yourself.

Bring something to do. Three hours is a long time to sit in a waiting room, especially when you feel queasy. A book, a tablet loaded with a show, or even a small pillow can make the difference between tolerable and miserable. You are typically allowed to sit quietly and move around a little, though vigorous walking can affect blood sugar levels and may be discouraged.

Eat a balanced dinner the night before that includes a normal amount of carbohydrates. You do not need to stuff yourself with bread, but a very low-carb meal the night before a fasting glucose test is the one dietary pattern that has been linked to potentially skewed results. Normal eating followed by the required overnight fast is the safest path to an accurate test.

When the Test Gets Repeated or Modified

If you vomit during the 3-hour test, most providers will ask you to come back and repeat it on another day. There is no reliable way to interpret partial results when the glucose load was not fully absorbed. Some offices will wait a week or so before scheduling the repeat, both to give you a break and because repeated concentrated glucose loads in a short period are not enjoyable.

Certain medical conditions can change how your provider approaches the test. People with a history of gastric bypass or sleeve gastrectomy, as mentioned earlier, face a much higher risk of dumping syndrome from the concentrated sugar load, which can cause severe nausea, diarrhea, and dangerously low blood sugar. In those cases, some providers will substitute alternative monitoring strategies, such as fasting glucose checks paired with after-meal glucose monitoring over several days, rather than subjecting the patient to a test their altered anatomy cannot handle safely.

Patients with hyperemesis gravidaris (severe pregnancy-related nausea) present a similar challenge. Keeping 100 grams of concentrated sugar solution down when you cannot keep most foods down is a tall order. Again, providers in this situation may opt for alternative monitoring or may try the test later in pregnancy when the nausea has improved. There is no universal protocol for these edge cases, so the plan usually comes down to a conversation between you and your provider about what is both safe and diagnostically useful.