Fasting and Timing for Gestational Diabetes Screening: How to Prepare for the Glucose Test

It is 7:40 on a weekday morning and a woman who is 26 weeks pregnant is sitting in a lab waiting room with a paper cup of something that tastes like flat orange soda concentrated four times. Her stomach is empty, her phone is at 12 percent, and she is quietly wondering whether the granola bar she ate at 9 the night before has just ruined everything.

Almost every pregnant person in the United States faces some version of this morning. The questions that surface online are remarkably consistent: how to prepare for glucose test pregnancy, what to eat before glucose test pregnancy, how many hours fasting glucose test pregnancy, and the one nobody says out loud at the clinic, how do I pass it.

The honest answers are less complicated than the forums suggest, and a few of the most popular tips are actively unhelpful. Here is what the evidence supports, test by test.

What is the glucose test in pregnancy actually measuring?

The glucose test is a measure of how efficiently your body clears sugar from the bloodstream after a fixed, known load. It is not a test of willpower, and it is not a snapshot of how much cake you ate at a baby shower. It is a stress test for insulin, the hormone that moves glucose out of the blood and into cells.

Pregnancy changes that system on purpose. The placenta produces hormones that make the mother’s tissues less responsive to insulin, a state called insulin resistance, so that more glucose stays in the blood and crosses to the growing baby. In most pregnancies the pancreas compensates by making more insulin. When it cannot keep up, blood sugar runs higher than it should, and that is gestational diabetes, which the CDC defines as diabetes first recognized during pregnancy in someone who did not have it beforehand.

The condition matters because sustained high maternal glucose reaches the baby, who responds by producing extra insulin and storing the surplus energy. The Mayo Clinic lists the downstream concerns: higher birth weight, a greater chance of a difficult delivery or cesarean birth, low blood sugar in the newborn, and a raised risk of type 2 diabetes later in life for the mother. None of these are certainties, and identifying the condition allows a team to manage it.

So the drink is a standardized dose of glucose, chosen precisely so that every person’s pancreas is asked the same question. The blood draw at a set time afterward records the answer. Everything about preparation exists to make sure the question is asked fairly, not to change the answer.

One-hour screen or two-hour tolerance test: which one will you have?

Confusion about fasting almost always comes from mixing up two different tests. Different countries, and different practices within the same country, use different approaches, and the preparation rules are not interchangeable.

Many US practices use a two-step approach. The first step is a glucose challenge test, sometimes called the one-hour test: you drink a 50-gram glucose solution without fasting and have blood drawn one hour later, according to the Mayo Clinic. If that result is above the practice’s threshold, you return for a three-hour oral glucose tolerance test, which requires fasting, a larger 100-gram drink and blood draws before and at hourly intervals afterward.

The NHS, and a growing number of US clinicians, use a single two-hour oral glucose tolerance test instead. You fast overnight, have a fasting blood sample, drink a 75-gram glucose solution and have a second sample two hours later. One visit, no screen beforehand.

Test	Fasting required?	Glucose drink	Blood draws	Time in clinic
One-hour glucose challenge (screen)	Usually no	50 g	1, at one hour	About 1 hour
Two-hour OGTT (diagnostic, NHS style)	Yes, overnight	75 g	2, fasting and at two hours	About 2 to 2.5 hours
Three-hour OGTT (US follow-up)	Yes, overnight	100 g	4, fasting then hourly	About 3 to 3.5 hours

The single most useful thing you can do is read your appointment letter or portal message and identify which row you are in. Everything else in this article branches from that one fact.

How many hours fasting for a glucose test in pregnancy?

For the one-hour screening test, the answer is usually none. MedlinePlus states plainly that you do not need to do anything special to prepare for the glucose challenge test. Some practices ask you to avoid eating in the hour or two before the drink, so a specific instruction from your own clinic overrides the general rule, but a required overnight fast is not standard for this step.

For the diagnostic tolerance tests the fast is real and it is not optional. MedlinePlus advises not eating or drinking anything other than sips of water for 8 to 14 hours before a glucose tolerance test. The NHS instructions for its two-hour test are similar: nothing to eat or drink except water for 8 to 10 hours beforehand. The Mayo Clinic describes fasting for at least eight hours before the three-hour test.

Those ranges are not arbitrary. Eight hours is roughly the time it takes for a normal meal to be fully absorbed so that your baseline reading reflects your own liver’s overnight glucose output rather than last night’s dinner. Beyond about 14 hours the body begins to shift its fuel use and fasting glucose can behave unpredictably, which is why labs set an upper limit too.

The practical translation, if your appointment is at 8 a.m., is that your last food and non-water drink should finish somewhere between 6 p.m. and midnight the night before, with most labs suggesting you stop by around 10 p.m. If the instructions say 10 hours and you finished dinner at 7:30, you are comfortably inside the window. Water is not only allowed but encouraged; a well-hydrated vein makes the blood draws far easier.

When the lab’s written instructions and a friend’s memory disagree, the lab wins. Different laboratories calibrate their reference ranges to their own protocol.

What to eat before a glucose test in pregnancy: the evening before

The most evidence-based advice about dinner the night before is also the least dramatic: eat the way you normally eat. MedlinePlus and the Mayo Clinic both instruct people to eat and drink normally for several days before a glucose tolerance test. The test is designed to be interpreted against a background of ordinary intake, and the thresholds that define an abnormal result were established in people who were eating normally.

A sensible last meal before a fasting test looks like any balanced dinner: a source of protein such as chicken, fish, beans or tofu, a portion of starch such as rice, potatoes or bread, and vegetables. Finish it before the cut-off time your lab gave you. There is no need to make it unusually small, and there is no benefit to making it unusually large.

Two moves that circulate online deserve a gentle correction. The first is a deliberately carbohydrate-free dinner, or a full day of avoiding carbohydrates, in the hope of a lower fasting reading. The second is loading up on sugar the night before so the body “gets used to it”. Neither reflects how the test works, and both are covered in more detail in the section on trying to pass the test. In brief: unusual eating in the days beforehand can push results in either direction and make the test less accurate rather than more favorable.

If you are having the one-hour screening test and it is scheduled for the afternoon, the same principle applies to lunch: a normal meal, eaten at a normal time. What you should not do is skip lunch and arrive with an empty stomach, because the screen was not designed for a fasting state and an empty stomach makes nausea from the drink more likely.

Is there a best breakfast before the 1-hour glucose test?

Searches for the perfect breakfast before the one-hour test are among the most common in this whole topic, and the popular answers tend to be some version of eggs, plain Greek yogurt and no carbohydrate at all. There is a logic to that advice, but it is worth understanding what it is really doing.

A high-carbohydrate breakfast eaten shortly before the drink stacks two glucose loads on top of each other, which can push the one-hour reading upward. A protein-based breakfast avoids that stacking. So far, so reasonable. The catch is that the glucose challenge test was designed and validated as a non-fasting test taken after ordinary meals, and it is a screen, not a diagnosis. Its job is to flag people who need the longer test. Engineering the breakfast to minimize the reading works against that purpose.

A middle path fits the evidence. If your appointment is early in the morning, eat an ordinary breakfast two to three hours beforehand, or follow your practice’s specific timing if they gave one. Something with protein and some whole-grain carbohydrate, for example eggs with a slice of whole-grain toast, oatmeal with nuts, or yogurt with fruit, is fine. Avoid arriving straight from a sugary coffee drink or pastry, not because it is forbidden, but because a large simple-sugar hit within the hour before the drink is the one thing likely to produce a misleadingly high screen.

Bring a snack for afterward. Many people feel shaky or ravenous once the blood is drawn, and the lab will not offer food. A small bag of nuts, a piece of fruit and a bottle of water in your bag is the most practical piece of preparation there is.

How to prepare for glucose test pregnancy: a 24-hour plan

Once you know which test you are having, the preparation fits on an index card. This plan assumes a morning appointment for a fasting tolerance test, which is the version that generates most of the anxiety; adapt the timings if yours differs.

The afternoon before, confirm the appointment time, the address and whether you need to check in at a lab or a clinic. Pack a bag: water bottle, a snack for afterward, a phone charger, a book or headphones, and something warm to wear because labs are often cold and cold hands make venous access harder. If you have young children, arrange care; the three-hour test in particular is not a good setting for a toddler.

Eat a normal dinner and finish it before the cut-off your lab specified. Drink water through the evening. Take any prescribed medicines exactly as your prescribing clinician has directed unless they have told you otherwise for this test; some medicines, including certain steroids, can affect glucose readings, so mention everything you take when you book and let the team decide.

In the morning, drink a glass of water when you wake. Skip coffee, tea, juice, chewing gum and mints, all of which can nudge glucose or trigger a stomach response. MedlinePlus also advises not smoking before the test. Arrive ten minutes early so you are calm rather than rushed, because acute stress raises glucose through adrenaline.

During the test, sit. Walking briskly around the building lowers glucose by pulling it into working muscle, which is why labs ask you to remain seated for the whole waiting period. After the final draw, eat your snack, drink water and take the rest of the morning gently. That is the whole of how to prepare for glucose test pregnancy; nothing on this card is exotic.

What should you avoid doing before the glucose test?

Most of the avoid list is about not accidentally altering the measurement. The items below apply mainly to the fasting tolerance tests; for the one-hour screen, only the last few are relevant.

• Eating or drinking anything other than water during the fasting window. This includes black coffee and unsweetened tea, which some labs tolerate and others do not; the safe default is water only.
• Chewing gum, mints and lozenges. Sugar-free varieties still stimulate saliva and digestive hormones, and some contain sugar alcohols. It is a small effect, but the fast is meant to be clean.
• Smoking or vaping. Nicotine affects glucose handling, and MedlinePlus specifically advises against smoking before the test.
• Exercising during the test. A walk to the coffee shop across the street between draws is the classic mistake; it lowers readings artificially and the lab may have to repeat the test.
• Dieting, fasting or carbohydrate-cutting in the days beforehand. Normal eating for several days is part of the test protocol.
• Arriving acutely ill. A fever, vomiting or a stomach bug both raises stress hormones and makes it unlikely you will keep the drink down. Call and reschedule.

One thing that does not belong on the avoid list is prescribed medication. Stopping a medicine on your own initiative to “clean up” a test result is not safe and can harm you and the pregnancy. If a medicine you take is known to affect glucose, the right step is to tell the team so they can interpret the result in context or, if they choose, adjust the timing. That is their decision, not something to work out in the waiting room.

Finally, avoid the temptation to compare your instructions with someone else’s. Two people in the same city can receive different, equally valid protocols from different labs.

How do I pass the glucose test while pregnant? Why gaming it backfires

This question deserves a straight answer rather than a scolding one. People ask it because a positive result feels like a verdict, and because a second, longer test means another morning off work and another needle. That is understandable. The problem is the framing.

A glucose test has no pass or fail. It has an accurate result or an inaccurate one. If your pancreas is currently keeping up with the extra demands of pregnancy, an honest test will show that. If it is not, an honest test will show that too, and finding out is the entire point. The Mayo Clinic notes that gestational diabetes often produces no symptoms at all, which is exactly why universal screening exists; you cannot feel your way to knowing.

Consider what the common tricks actually do. Cutting carbohydrates for three days lowers your body’s insulin secretion in response to a load, so when the glucose drink arrives, the pancreas is less primed and readings can come out higher, not lower. Walking around during the test drives glucose into muscle and produces a falsely low reading. A falsely low reading does not mean the baby is unexposed to high sugar for the remaining trimester; it means nobody is watching.

The cost of a missed diagnosis is borne by the pregnancy, not by the test. The CDC estimates that 5 to 9 percent of pregnancies in the United States are affected by gestational diabetes each year, and most of those people had no idea before the test. Identified early, the condition is usually managed with eating changes and activity, with medication added only when the treating team judges it necessary.

So the truthful answer to how to pass is: eat normally, follow the fasting instruction if you were given one, sit still, and let the test tell you what is real. A result you can trust is the only kind worth having.

How long does the glucose test take in pregnancy, and what happens in the room?

Timing anxiety is easier to manage once the sequence is predictable, so here is the day as it usually unfolds.

For the one-hour screen, you check in, possibly have a quick weight and blood pressure check, and drink the glucose solution. The drink is typically chilled and comes in orange, lemon-lime or fruit punch flavors. Most labs want it finished within about five minutes and will note the time. You then wait, seated, for one hour, and a single blood sample is taken from a vein in your arm. Total time is a little over an hour.

For the two-hour test used by the NHS and many US practices, a fasting sample is taken first, you drink the solution, and a second sample is taken two hours later. Expect around two and a half hours door to door. For the three-hour test, a fasting sample is followed by the drink and then samples at one, two and three hours, so plan on three and a half hours.

The blood draws feel like any routine draw: a tourniquet, a brief sting, a cotton pad. Some labs keep a small cannula in place to avoid repeated needle sticks; others draw fresh each time. If you know your veins are difficult, say so at the start and drink water in the days beforehand.

You will be asked to stay in or near the waiting area and not to eat, drink anything but water, or walk around. Bring low-stimulation entertainment; something absorbing enough to pass the time without pacing.

Results from the one-hour screen often come back within a day or two. Tolerance test results may take a little longer because multiple samples are processed. Your practice will tell you how they communicate results, whether by portal, phone call or at your next visit.

Who is screened, when, and who is asked to test earlier or wait?

Most pregnant people are offered glucose testing between 24 and 28 weeks of pregnancy, the window recommended by both the NHS and the Mayo Clinic. That timing is deliberate. Placental hormones that drive insulin resistance rise sharply through the second trimester, so testing earlier can miss cases that develop later, while testing much later leaves less time to act on a result.

Some people are asked to test earlier. The NHS advises that anyone who had gestational diabetes in a previous pregnancy should be offered testing soon after their first antenatal appointment, and then again at 24 to 28 weeks if the first result is normal. US practices commonly take the same approach for people with prior gestational diabetes or with risk factors that raise the possibility of undiagnosed type 2 diabetes before pregnancy.

The NHS lists the factors that increase risk: a body mass index above 30, a previous baby weighing 4.5 kg (about 10 lb) or more at birth, gestational diabetes in a previous pregnancy, a parent or sibling with diabetes, and South Asian, Black, African-Caribbean or Middle Eastern family background. In the UK these factors determine who is offered the test; in the US, screening is generally offered to everyone regardless of risk, with risk factors influencing timing.

Who is asked to wait? Someone with an acute illness, active vomiting or a recent hospital admission is usually rescheduled, because both illness and stress hormones distort readings. People taking medicines known to raise glucose, such as certain steroids, may have the test timed around a course. And someone who already has a diabetes diagnosis before pregnancy does not need a screening test at all; they are cared for on a different pathway from the start.

If you are unsure which group you belong to, ask. The schedule is set by your care team, and it is theirs to adjust.

Feeling sick, dizzy or faint on the day: what helps and what to report

The drink is sweet in a way few people enjoy, and on an empty stomach in pregnancy it can provoke nausea, a hot flush, light-headedness or a wave of tiredness an hour or two later. These reactions are common and usually pass. A few practical things reduce their odds.

Drink the solution steadily rather than in one gulp; most labs allow up to five minutes. Chilled solution goes down more easily than room temperature, and some labs will let you sip water afterward to rinse the taste. Sit rather than stand while waiting, because the combination of fasting, a sugar spike and pregnancy’s lower blood pressure can make standing up quickly feel unsteady. Bring a cool cloth or a small fan if you tend to flush.

Vomiting is the one event that changes the plan. If you bring up the drink, the lab cannot know how much glucose was absorbed, and the test is typically stopped and rescheduled. Tell staff immediately rather than trying to push through, and do not attempt to redrink from a second bottle on your own initiative.

Once the final draw is done, eat the snack you packed. Pairing carbohydrate with protein, for example an apple with peanut butter or crackers with cheese, tends to settle the post-test dip more comfortably than sugar alone.

If you have a history of fainting with blood draws, mention it at check-in. Lying down for the draw and being given a minute to sit afterward is standard practice and entirely reasonable to request. None of these responses to the drink predict your result; feeling awful during the test says nothing about whether the reading will be normal.

What people often get wrong about how to prepare for the glucose test in pregnancy

Some myths about this test are harmless. Others cause real problems, either by producing unreliable results or by adding fear where none is needed. Here are the ones most worth correcting.

“You have to fast for every glucose test.” Not so. The one-hour screening test is a non-fasting test; MedlinePlus states that no special preparation is needed. Only the diagnostic tolerance tests require an overnight fast.

“Cutting carbs for a week beforehand gives a better result.” The opposite is closer to the truth. Both MedlinePlus and the Mayo Clinic instruct people to eat normally for several days before a tolerance test, because unusually low carbohydrate intake can impair the insulin response and raise readings.

“A high screen means I have gestational diabetes.” A screening test is designed to cast a wide net. Many people with an elevated one-hour result go on to have a normal three-hour test. The screen identifies who needs the fuller test; it does not diagnose.

“Gestational diabetes means I did something wrong.” The driver is placental hormones acting on insulin sensitivity, and the strongest risk factors, including family history and ethnicity, are not choices. Sugar intake during pregnancy does not cause the condition.

“Black coffee doesn’t count as breaking a fast.” Caffeine affects glucose handling, and many labs specify water only. When in doubt, water.

“A normal result means I’m in the clear for the whole pregnancy.” Mostly yes, but insulin resistance keeps rising into the third trimester, and if new signs appear, such as a baby measuring large on ultrasound or excess fluid, a clinician may retest.

“Skipping the test is an option if I feel fine.” The Mayo Clinic notes that most people with gestational diabetes have no noticeable symptoms. Feeling fine is exactly what the condition looks like from the inside.

What the days and weeks after the glucose test usually look like

Three paths open after the blood is drawn, and knowing the shape of each in advance removes much of the dread.

The most common path is a normal result. You will usually hear within a few days, and routine antenatal care continues unchanged. No special diet is required. If your practice used the one-hour screen, a normal result ends the glucose testing for this pregnancy unless something later prompts a recheck.

The second path is an elevated screen followed by a normal tolerance test. This is a frequent outcome and can feel like whiplash: a worried phone call, a longer fasting test, and then reassurance. The Mayo Clinic describes the diagnostic test as positive only when two or more of the readings exceed the thresholds; a single high value on the screen does not carry that weight. Once the tolerance test is normal, care returns to the routine schedule.

The third path is a diagnosis of gestational diabetes. What follows is more structured but rarely dramatic. Most teams arrange an appointment with a dietitian or diabetes educator within a week or two, teach you to check your own blood sugar at home, and set individual targets. The Mayo Clinic notes that many people manage the condition with eating changes and regular physical activity alone. When those are not enough, a clinician may prescribe insulin, which is a replacement for the hormone the pancreas cannot produce in sufficient quantity, or an oral medicine that improves insulin sensitivity. Whether, when and which is entirely the prescribing clinician’s decision, informed by your readings.

Ultrasound scans to track the baby’s growth are often added, and the team will discuss birth planning with you. After delivery, blood sugar usually returns to normal as placental hormones disappear, and the NHS advises a follow-up glucose test around 6 to 13 weeks after birth, then ongoing checks, because a history of gestational diabetes raises the long-term risk of type 2 diabetes.

Questions to ask your care team before the glucose test

Ten minutes of questions when the test is booked prevents most of the confusion that fills online forums. These are worth asking, and writing the answers down.

• Which test am I having: the one-hour screen, the two-hour tolerance test or the three-hour tolerance test?
• Do I need to fast, and if so, for exactly how many hours? Is water allowed, and what about black coffee or tea?
• Is there anything specific I should eat or avoid the day before?
• Should I take my usual medicines and supplements that morning, including prenatal vitamins and any prescribed treatment?
• How long should I plan to be at the lab, and can I bring someone with me?
• What happens if I am unable to keep the drink down?
• How and when will I receive results, and what number do I call if I have not heard by that time?
• If the screen is elevated, how soon would the follow-up test be scheduled, and does it use the same preparation?
• Are there reasons in my history that would make you test me earlier or repeat the test later in pregnancy?
• If the result shows gestational diabetes, what are the first steps, and who will I see?

Two of these matter more than the rest. The first question, which test, determines everything about preparation. The fourth, about medicines, protects you from a common and dangerous impulse to stop something on your own before a test. Prescribed treatment should be continued unless the prescribing clinician says otherwise, and the team may simply record what you take so the result can be read in context.

Bring these answers with you on the day. Lab staff and clinic staff sometimes give slightly different verbal instructions, and having your team’s written answer settles it quickly.

When to call your doctor

The glucose test itself is low-risk, and most people go home with nothing more than a sore arm and a strong desire for lunch. A few situations, before or after the test, do warrant a call rather than waiting for the next appointment.

Around the test, contact your care team if you cannot keep the drink down and are unsure how to reschedule; if you feel faint and it does not settle after sitting for a few minutes and eating; or if you develop swelling, spreading redness or significant pain at the blood draw site over the following day, which can signal a local infection or a deeper bruise.

More broadly in pregnancy, whether or not your glucose test has happened yet, some signs need same-day attention. Call promptly for: unusual and persistent thirst with very frequent urination; blurred vision; severe headache that does not ease with rest; sudden swelling of the face, hands or feet; pain under the ribs on the right side; vaginal bleeding; leaking fluid; a noticeable decrease in the baby’s movements after about 28 weeks; or vomiting that stops you keeping fluids down for more than a day. Several of these overlap with pre-eclampsia, a blood-pressure disorder of pregnancy, and none of them should wait for a routine visit.

If you have been diagnosed with gestational diabetes and are checking your own blood sugar, your team will have given you a threshold above or below which to call. Follow their instruction rather than a number from the internet, and call if you have symptoms of low blood sugar such as shakiness, sweating and confusion after starting any treatment.

Emergency services are the right call for chest pain, difficulty breathing, a seizure, heavy bleeding or loss of consciousness. Every other question in this article belongs with your treating team, who know your history and your results.

Frequently asked questions

What should I eat before a glucose test during pregnancy?

Eat the way you normally do. For the one-hour screening test, an ordinary meal two to three hours beforehand is fine; avoid a large sugary drink or pastry within the hour before the glucose solution. For the fasting tolerance tests, have a normal balanced dinner that finishes before your lab’s cut-off time, then only water until the test. MedlinePlus and the Mayo Clinic both advise several days of normal eating beforehand.

How many hours do I need to fast for the glucose test in pregnancy?

It depends on the test. The one-hour glucose challenge usually needs no fasting at all. The two-hour and three-hour oral glucose tolerance tests require an overnight fast, which MedlinePlus gives as 8 to 14 hours and the NHS as 8 to 10 hours, with water allowed throughout. Always follow the specific number your own lab gives you, because reference ranges are calibrated to their protocol.

How do I pass my glucose test while pregnant?

There is no passing or failing, only an accurate result or a distorted one. Eat normally in the days before, follow any fasting instruction, sit still during the test and avoid gum, coffee and smoking. Tricks such as cutting carbohydrates or walking between draws can make readings unreliable, and a falsely low result leaves untreated high blood sugar reaching the baby. A trustworthy result is the goal.

What is the best breakfast to eat before a 1-hour glucose test?

An ordinary breakfast eaten two to three hours before the appointment, unless your practice gave different timing. Something with protein and some whole-grain carbohydrate, such as eggs with whole-grain toast or oatmeal with nuts, is sensible. The test is designed as a non-fasting screen, so skipping breakfast is not necessary and can worsen nausea. Avoid a large simple-sugar hit right before the drink.

What should I avoid doing before a glucose test during pregnancy?

For the fasting tests, avoid all food and drink except water, including black coffee, gum and mints. For any version, avoid smoking or vaping, avoid exercising during the test, and do not diet or cut carbohydrates in the days beforehand. Reschedule if you have a fever or a stomach bug. Do not stop any prescribed medicine on your own; tell your team what you take and let them decide.

How long does the glucose test take in pregnancy?

The one-hour screen takes a little over an hour: drink the solution, wait seated, one blood draw. The two-hour tolerance test involves a fasting draw, the drink and a second draw two hours later, so about two and a half hours in total. The three-hour test adds hourly draws and runs roughly three and a half hours. Bring water, a snack for afterward and something to occupy you.

Can I drink water before the glucose test?

Yes. Water is allowed during the fasting window and is actively helpful, because being well hydrated makes veins easier to access for blood draws. What is not allowed before a fasting test is anything with calories or flavor, including coffee, tea, juice, sports drinks and chewing gum. If your lab’s instructions differ from this general rule, follow the lab.

What happens if I throw up the glucose drink?

Tell the lab staff straight away. Once the drink is vomited, there is no way to know how much glucose was absorbed, so the test is usually stopped and rescheduled for another day. Do not try to drink a second bottle on your own. Sipping the solution slowly over five minutes, having it chilled and staying seated all reduce the chance of nausea.

Does a high one-hour glucose result mean I have gestational diabetes?

No. The one-hour test is a screen designed to identify people who need the longer diagnostic test, and many people with an elevated screen go on to have a normal tolerance test. According to the Mayo Clinic, the diagnostic test is considered positive only when two or more of its readings exceed the thresholds. Your care team will explain your specific numbers and the next step.

Why is the glucose test done at 24 to 28 weeks?

Placental hormones that make the body less responsive to insulin rise sharply through the second trimester, so the NHS and Mayo Clinic recommend testing between 24 and 28 weeks, when the effect is measurable but there is still time to manage a diagnosis. People with gestational diabetes in a previous pregnancy are usually offered an earlier test soon after booking, and again at 24 to 28 weeks if the first is normal.

References

• NHS: Gestational diabetes
• MedlinePlus: Glucose screening tests during pregnancy
• CDC: About gestational diabetes

This article is for general information only and is not a substitute for professional medical advice. Please consult a qualified doctor about your individual situation.