Glucose Test During Pregnancy: What to Expect

Between your 24th and 28th week of pregnancy, you’ll likely receive the same message from your doctor: “Time for your glucose test.” For some parents-to-be, this solitary appointment creates more anxiety than the ultrasounds, weigh-ins, or even labor itself, primarily because no one ever tells you what to expect.

The glucose test during pregnancy, officially called the oral glucose tolerance test (OGTT), screens for how your body is handling sugar. There’s a reason your doctor recommends it: it helps identify gestational diabetes, a condition that can develop during pregnancy and may affect both you and your baby if left unmanaged. This test aims to spot gestational diabetes mellitus (GDM), a type of diabetes that occurs solely during pregnancy, so we can ensure the well-being of both mother and child. [1]

Pregnant woman reviewing lab results with her doctor during a prenatal visit

What Is the Glucose Test During Pregnancy?

The glucose test evaluates how well the body is able to remove sugar from the blood when the patient drinks a specially made and extremely sweet glucose solution. The effects of pregnancy predispose the body to become insulin-resistant due to placental hormones, and some women develop GDM [2].

Undetected GDM has been associated with large birth weights, cesarean deliveries, low glucose levels in infants, and increased chances of developing type 2 diabetes mellitus in mother and baby over the course of their lifetimes [1][3]. For this reason, almost all medical authorities, including ACOG and ADA, advocate universal testing between 24 and 28 weeks gestation [2].

Why Doctors Order the Glucose Test

Doctors do not perform this test to scare you; they perform it because gestational diabetes rarely shows any symptoms. A person can be feeling totally well but having high blood sugar levels that affect the growth of the baby.

Who Is at Higher Risk?

Certain factors make women vulnerable to GDM to an extent where certain professionals do testing even before 24 weeks, at their first prenatal appointment [2]. Body Mass Index of 30 or above; personal experience with GDM; family history of type 2 diabetes; polycystic ovary syndrome; being over the age of 35; and being of certain ethnic origin such as South Asian, Southeast Asian, and Hispanic [2]. It must be stressed that even if there are no risks present, all mothers-to-be will be screened.

The Two Main Types of Glucose Tests

Not all clinics follow the same protocol. There are two types of protocols, depending on which clinic you go to.

Lab technician preparing blood sample tubes for a gestational diabetes glucose test

The One-Step Test (75g OGTT)

The patient will fast all night, will ingest a 75-gram glucose solution, and will have their blood sampled at the one and two-hour intervals, along with their fasting glucose levels. This protocol uses IADPSG guidelines that resulted from the findings of an international, multicenter study known as the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study headed by Dr. Boyd Metzger of the Feinberg School of Medicine at Northwestern University [3]. This study, conducted on more than 25,000 pregnant women in 15 different centers around the world, proved that any level of blood sugar, even lower than diabetic levels, was associated with increasing rates of pregnancy complications with no specific safe cutoff point [3].

The Two-Step Test (50g Challenge, Then 100g if Needed)

This older, still widely used approach starts with a shorter screening: a 50-gram glucose drink with no fasting required, followed by a single blood draw an hour later. A high result triggers a longer three-hour, 100-gram diagnostic test. This method traces back to criteria first proposed by researchers John B. O'Sullivan and Claire M. Mahan in 1964, whose work laid the foundation for gestational diabetes diagnosis for the following six decades [4]. Their thresholds were later refined by Dr. Marshall Carpenter and Dr. Donald Coustan into what's still known today as the Carpenter-Coustan criteria.

How to Prepare for Your Glucose Test

Preparation genuinely affects how accurate your results are, so it's worth taking seriously.

The Night Before

Consume a regular, balanced meal; this is not the occasion to "prepare" yourself with an extremely low or high carbohydrate intake diet, as it may distort the outcomes. If the test involves fasting (which happens to be the case in the 75 g form of the glucose tolerance test), avoid eating or drinking anything other than water 8-14 hours before the test.

The Morning Of

Bring something to keep yourself occupied as you might have to wait between one to three hours. Make sure that you are wearing a short-sleeved shirt so that blood samples can be taken easily from your arm. Also, try not to engage in strenuous activity just prior to the test as it could lower your blood sugar level.

During the Test

You will consume the glucose solution, which is usually flavored like flat orange juice or cola, within five minutes. The solution tastes sweet compared to any other soft drink; people may experience slight nausea, restlessness, and lightheadedness before drawing blood. Slowly drinking the glucose solution, if allowed, or sitting in a cool environment may ease these symptoms.

Bottle of orange-flavored glucose solution used for pregnancy glucose screening

Understanding Your Glucose Test Results

This is the part most people find genuinely confusing, so here's a plain-language breakdown using the current ADA 2025 thresholds for the 75-gram one-step test [5]:

Timing	Normal	Flagged as High
Fasting	Below 92 mg/dL	92 mg/dL or above
1 hour after drink	Below 180 mg/dL	180 mg/dL or above
2 hours after drink	Below 153 mg/dL	153 mg/dL or above

With the single-step process, all that is required is one raised value [5]. With the old two-step process, where the glucose load was 100g three hours, the requirement in almost all laboratories was two or more values of raised glucose from four points (fasting, 1 hour, 2 hours, 3 hours).

What If Only One Number Is Borderline?

OGTT pattern research indicates that whether the high number is a fasting number, a one-hour number, or a combination of numbers from various points affects how your pregnancy is handled; an isolated abnormality at fasting, for example, has been linked to an increased risk of having to be put on insulin therapy than an isolated abnormality at post-meal tests [6]. Your health care provider will consider what specific number was high.

What Happens If You're Diagnosed With Gestational Diabetes

GDM is not a failure and is extremely manageable for the vast majority of people. Next steps include:

Consulting a dietitian about meals low in glycemic index
Blood sugar testing done daily at home using a glucometer
Physical activity every day, for example, going for a walk after eating
More ultrasounds to check on fetal growth

Medications (insulin and sometimes metformin) if other efforts cannot maintain proper sugar levels

Pregnant woman checking her blood sugar with a home glucometer as part of gestational diabetes management

Nevertheless, according to available recommendations, there is no need for any treatment, because nearly all patients with gestational diabetes can manage this condition by modifying their lifestyle only, while blood sugar levels become normal soon after delivery. However, according to the latest guidelines, glucose testing should be repeated 6-12 weeks after delivery, because more than a third of women with a previous history of GDM suffer from glucose intolerance afterwards. This fact may make such an evaluation not very noticeable, but highly necessary [7]. Moreover, many physicians take into account this history during subsequent pregnancies, because previous history of GDM is the most powerful predictor of recurrence of gestational diabetes in the future pregnancy, and glucose screening is recommended to be performed as early as at the first prenatal visit [2].

Coping With Test-Day Nausea and Anxiety

Should the liquid bother you more than the syringe, do not be alarmed; nausea and vomiting are frequent enough that repeat tests may be necessary [8] due to failure to keep the liquid down during the first try. A couple of tips that would make your testing experience more tolerable include drinking slowly where possible, bringing some food for after the last draw, scheduling the test early in the morning, and taking slow breaths while waiting.

Frequently Asked Questions (FAQs)

Q1: How long does the pregnancy glucose test take?

The one-hour screening takes about 90 minutes total once you factor in the wait and blood draw. The full diagnostic version can take three to four hours.

Q2: Can I drink water during the glucose test?

Generally, yes, plain water is allowed and often encouraged, but always confirm with your provider or the lab beforehand.

Q3: Is it normal to feel shaky or nauseated after drinking the glucose solution?

Yes, mild shakiness, sweating, or nausea are common reactions to the sudden sugar load and usually pass once the test is finished and you've eaten.

Q4: Does failing the one-hour test mean I have gestational diabetes?

Not necessarily. Under the two-step method, an elevated one-hour result only means you need the longer three-hour confirmatory test; many people who fail the first screen have normal results on the second.

Q5: Can gestational diabetes go away after pregnancy?

In most cases, yes, blood sugar returns to normal after delivery. However, having GDM does raise the long-term risk of developing type 2 diabetes later in life, which is why postpartum follow-up testing matters [7].

Q6: What foods should I avoid before the test?

There's no need for a special diet beforehand; eating unusually low-carb or high-carb in the days before can actually distort your results. Eat normally, then follow the fasting instructions exactly as given.

Key Points

The oral glucose tolerance test during pregnancy is used to check for gestational diabetes, usually at 24-28 weeks, though women with increased risk factors are screened sooner [1][2].
Two main methods are used: the 75 g test (fasting necessary; one high value indicates GDM) and 50g/100g two-step test (fasting not necessary for the first stage; at least two high values are required for the second) [3][5].
Proper preparation includes eating regular meals before, adhering strictly to fasting if you need it for the test, and avoiding intensive physical activity prior to the test.
Feelings of mild sickness, dizziness, or shakiness right after drinking the solution are normal.
Gestational diabetes diagnosis doesn't mean failure and is usually easily treated through proper diet and exercise.
Follow-up screening is recommended postpartum, since GDM increases the risk of developing type 2 diabetes later in life [7].