Gestational diabetes screening is a standard prenatal test performed between 24 and 28 weeks of pregnancy to detect high blood sugar levels that can develop during pregnancy. The American College of Obstetricians and Gynecologists recommends this screening for all pregnant people because it identifies a condition affecting approximately 6% of pregnancies, allowing treatment to prevent serious complications for both mother and baby.
Screening is a simple blood test—either a nonfasting glucose screen or a fasting glucose tolerance test. Most women receive normal results and proceed without further testing; of those who screen positive initially, about three-quarters will not meet diagnostic criteria on follow-up testing. Understanding what the screening involves, when it happens, and what results mean helps you prepare and make informed decisions about your care.
Table of Contents
- Why Gestational Diabetes Screening Happens in the Second Trimester
- The Two Approaches to Gestational Diabetes Screening
- Preparing for Your Screening Test
- What the Test Results Mean
- If Your Initial Screen Is Elevated
- Risk Factors and Who Gets Earlier or More Intensive Screening
- What Happens After a Gestational Diabetes Diagnosis
- Managing Gestational Diabetes Day to Day
- Complications to Watch For and When to Call Your Provider
- Life After Gestational Diabetes Screening and Diagnosis
- Frequently Asked Questions
Why Gestational Diabetes Screening Happens in the Second Trimester
Gestational diabetes is a temporary condition in which pregnancy hormones interfere with your body's ability to use insulin effectively, raising blood sugar levels. It does not mean you have diabetes before pregnancy or will develop it afterward—though people with gestational diabetes have a higher risk of type 2 diabetes later in life. ACOG recommends screening between 24 and 28 weeks of gestation because this window balances two competing factors.
Early in pregnancy, pregnancy hormones increase gradually; by the second trimester, insulin resistance is often pronounced enough to detect. Screening before 24 weeks lacks evidence of benefit, and detecting gestational diabetes too early does not improve outcomes for your baby. Untreated gestational diabetes increases the risk of serious complications. The most common is fetal macrosomia—a baby's birth weight exceeding 4,500 grams (about 10 pounds)—which can cause shoulder dystocia (the baby's shoulder becomes stuck during delivery) and neonatal hypoglycemia (dangerously low blood sugar in the newborn).
Treatment during pregnancy reduces macrosomia risk by approximately 47%, making screening and early intervention protective. Gestational diabetes also increases your own risk of preeclampsia and infection during pregnancy. These risks decline significantly with treatment, including glucose monitoring, dietary changes, exercise, and medication if needed. This is why your provider offers screening as standard care: the test is simple, the condition is manageable, and early detection prevents harm.
You do not need screening before 24 weeks unless you have specific risk factors. These include a body mass index of 25 kg/m² or higher, a family history of diabetes, a prior gestational diabetes diagnosis, or being age 35 or older. If any of these apply, ask your provider whether earlier screening is appropriate for your situation.
The Two Approaches to Gestational Diabetes Screening
your provider may recommend either a two-step screening process or a one-step test. Both are valid; the choice depends on your care setting and your provider's preference. Knowing the difference helps you understand what to expect and why your appointment schedule looks the way it does.
The two-step approach begins with a nonfasting 50-gram glucose screen—you do not need to fast beforehand, and you can take the test at any time of day. You drink a sweet beverage containing 50 grams of glucose and have your blood drawn one hour later. This is a preliminary screen only; about 20% of pregnant people have elevated results, but most do not actually have gestational diabetes.
If your 50-gram screen is elevated, you proceed to a diagnostic 100-gram oral glucose tolerance test (OGTT). This test requires a 12-hour overnight fast. You drink a glucose beverage containing 100 grams and have blood drawn at fasting, one hour, two hours, and three hours. Two elevated values out of the four measurements confirm gestational diabetes.
This two-step method reduces unnecessary confirmatory testing for those with normal initial screens. The one-step approach uses a 75-gram OGTT performed after a 12-hour fast, with blood drawn at fasting, one hour, and two hours. Gestational diabetes is diagnosed when any one value meets or exceeds fasting glucose of 5.1 mmol/L, 1-hour glucose of 10.0 mmol/L, or 2-hour glucose of 8.5 mmol/L.
This approach identifies all cases in one visit but requires one fasting test rather than a nonfasting screen followed by fasting confirmation. Both methods have advantages. The two-step approach reassures most women immediately that no further testing is needed. The one-step approach reaches a diagnosis faster if you do screen positive, avoiding a wait between screening and confirmation. Ask your provider which method they offer and which fits your schedule and preferences.
Preparing for Your Screening Test
Preparation depends on which test you receive. If you are having the nonfasting 50-gram screen, minimal preparation is required—you can eat and drink normally beforehand. Bring a snack to eat after the test if you feel faint or dizzy, though this is uncommon. The test itself takes only a few minutes. If you are having the 75-gram OGTT (whether as a one-step screening or as the diagnostic follow-up to an elevated 50-gram screen), you must fast for 12 hours beforehand.
Your provider typically asks you to consume at least 150 grams of carbohydrates per day for the three days before the test to ensure reliable results. This means eating normally without restriction—not an unusual dietary change for most people. Plan your fasting period strategically. If your test is scheduled for 8 a.m., stop eating and drinking (except water) at 8 p.m.
the night before. You may take your prenatal vitamins with water. If you take medications, ask your provider whether to take them on the day of your fasting test; some medications affect glucose results. Wear loose, comfortable clothing and bring your insurance card. The testing center may draw blood from your arm multiple times, so avoid sleeves that are difficult to roll up.
Bring something to read or do during waits; the one-hour period between your first blood draw and second can feel long. Stay hydrated during fasting. Drink water freely; dehydration can make blood draws more difficult and may affect test results. Avoid caffeine, which can elevate blood glucose. If you feel dizzy or unwell after fasting, let your healthcare provider know—they may reschedule or adjust the timing to ensure safe testing.
Many testing centers allow you to bring a support person. If anxiety about the test or needles is a concern for you, having someone present can be helpful. Some people find it easier to fast if they go to the appointment early in the morning when they have been fasting overnight naturally.
What the Test Results Mean
Results are given as milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L) depending on your lab. If you receive the 50-gram nonfasting screen, a glucose level below 140 mg/dL (7.8 mmol/L) is considered normal; you are done with screening for gestational diabetes. A result of 140 mg/dL or higher does not mean you have gestational diabetes—it means your initial screen was elevated and you need the diagnostic test.
Of people who screen positive on the 50-gram test, approximately 75% actually have normal results on the confirmatory 100-gram test. This is why a second test is done; the initial screen has a high false-positive rate by design, catching most cases at the cost of testing many women who do not have the condition. For the diagnostic 100-gram OGTT, your lab compares all four blood draws to threshold values.
Gestational diabetes is confirmed if two or more values are at or above the thresholds: fasting 95 mg/dL, 1-hour 180 mg/dL, 2-hour 155 mg/dL, or 3-hour 140 mg/dL. If only one value is elevated, the result is considered normal for gestational diabetes screening. The one-step 75-gram OGTT uses different thresholds: fasting 92 mg/dL (5.1 mmol/L), 1-hour 180 mg/dL (10.0 mmol/L), or 2-hour 153 mg/dL (8.5 mmol/L).
A single elevated value confirms gestational diabetes; this approach is more sensitive and identifies approximately 10% more cases than the two-step method. When results arrive, your provider explains them and discusses next steps. Many providers call with normal results, so expect contact within a few days of testing. If your results show gestational diabetes, your provider schedules follow-up appointments to begin management, usually including a visit with a diabetes educator or maternal-fetal medicine specialist. Ask your provider for your actual numbers, not just "normal" or "abnormal." Some women benefit from seeing how close or far they are from the diagnostic threshold, and your complete results create a baseline for monitoring if you are diagnosed.
If Your Initial Screen Is Elevated
An elevated 50-gram screen result is common and does not automatically mean gestational diabetes. Your provider calls and schedules the diagnostic 100-gram test, usually one to two weeks later. During the wait, you may feel anxious; remember that this is a normal part of careful prenatal care. Before your diagnostic test, your healthcare provider typically provides written instructions for fasting and the three-day carbohydrate preparation.
Some providers ask you to keep a brief food diary before the test. This information helps identify whether dietary factors contributed to the elevated screen and guides conversation if your diagnostic test is also high. If your diagnostic test shows gestational diabetes, your provider discusses management immediately. You receive referrals to a diabetes educator, a registered dietitian, and possibly an endocrinologist or maternal-fetal medicine specialist.
Your first appointments cover blood glucose monitoring, dietary adjustment, and realistic activity goals. Many people manage gestational diabetes successfully with these changes alone; others need medication. If your diagnostic test is normal, your gestational diabetes screening is complete. You do not need repeated testing unless you develop new risk factors or symptoms like unusual thirst or increased urination. Congratulate yourself on completing this important screening; you have taken a step to protect both your health and your baby's.
Risk Factors and Who Gets Earlier or More Intensive Screening
Some pregnant people are at higher risk of gestational diabetes and may receive screening earlier or more frequently. Knowing your own risk factors helps you understand why your provider may recommend a different screening timeline. You are at higher risk if your body mass index (BMI) is 25 kg/m² or higher before pregnancy. BMI is weight in kilograms divided by height in meters squared; a provider or nurse can calculate this quickly.
Higher BMI increases insulin resistance, which becomes amplified during pregnancy. If your BMI is 25 or above, ask whether your provider recommends screening before 24 weeks. A family history of type 2 diabetes in a first-degree relative (parent or sibling) significantly increases your risk. This is true even if you have never had gestational diabetes.
Your provider may discuss screening before 24 weeks if this applies to you, along with lifestyle measures like consistent physical activity. Prior gestational diabetes is a strong predictor of recurrence. If you had gestational diabetes in a previous pregnancy, expect screening earlier and possibly more frequent monitoring. Some providers recommend a fasting glucose check as early as the first prenatal visit for these individuals, before 24-week screening begins.
Age 35 and older at delivery is considered a risk factor, though gestational diabetes occurs across all ages. Some providers recommend earlier screening at this age; others rely on the standard 24-week timeline. Discuss your personal risk with your provider. Other factors include ethnic background (higher rates in Hispanic, Native American, Pacific Islander, and some Asian populations), a prior high-birth-weight baby, polycystic ovary syndrome, and acanthosis nigricans (dark skin patches often associated with insulin resistance). If you have any of these, mention them at your next visit.
What Happens After a Gestational Diabetes Diagnosis
If gestational diabetes is confirmed, your care team moves quickly to begin management. You may feel overwhelmed; this is normal. The good news is that most women manage gestational diabetes successfully, and treatment significantly reduces risks for both mother and baby. Your provider refers you to a registered dietitian who specializes in gestational diabetes. This person teaches carbohydrate counting, portion sizes, meal timing, and food choices that keep blood glucose stable.
You typically learn that you do not need to eliminate foods, but instead balance meals and snacks to prevent high blood sugar spikes. You receive a blood glucose monitor, lancets, and test strips. Home glucose monitoring is central to gestational diabetes management. You typically check your fasting glucose every morning and glucose one to two hours after each meal.
Your provider or educator reviews your logs and helps you identify patterns. Most women check glucose four to six times daily. Exercise is encouraged as part of treatment. Physical activity helps your muscles use glucose effectively, reducing blood sugar levels. Aim for 150 minutes of moderate-intensity activity per week if you were active before pregnancy, or work toward activity as tolerated if you are newly active.
Walking, swimming, and stationary cycling are safe during pregnancy. Many women's blood glucose improves with diet and exercise alone. If glucose levels remain elevated despite these changes, medication is added. Insulin is the first-line medication; it does not cross the placenta and is completely safe in pregnancy. Metformin is sometimes used and also does not cross the placenta.
Your provider discusses which medication fits your situation. You see your provider more frequently once gestational diabetes is diagnosed—typically every one to two weeks instead of monthly. These visits monitor your blood glucose control, check your blood pressure, and assess your baby's growth. You may have additional ultrasounds to monitor your baby's size.
Managing Gestational Diabetes Day to Day
Living with gestational diabetes requires attention but is manageable for most pregnant people. The day-to-day reality involves blood glucose monitoring, meal planning, and activity, but most women report that these changes become routine within weeks. Blood glucose monitoring is the cornerstone of management. You check your fasting glucose before eating or drinking anything except water each morning.
You also check one to two hours after the start of each meal. Your provider gives you target ranges—typically fasting below 95 mg/dL and postmeal below 140 mg/dL, though individual targets vary. Meal timing matters significantly. Spreading carbohydrates across meals and snacks prevents large glucose spikes. A typical pattern is three meals and two to three snacks daily, with carbohydrates distributed evenly.
Eating protein and fat with carbohydrates slows glucose absorption, keeping levels more stable. Foods that affect gestational diabetes management include refined carbohydrates (white bread, sugary drinks, pastries), which raise blood glucose quickly. Foods that stabilize glucose include whole grains, legumes, non-starchy vegetables, lean proteins, and healthy fats. Your dietitian helps identify specific foods that work for your body; tolerance varies from person to person.
Many women worry about medication during pregnancy, but insulin and metformin are well-studied and safe. If your provider recommends medication, this is not failure; it reflects the reality that pregnancy hormones interfere with insulin action in ways diet and exercise cannot fully overcome. Medication ensures your baby receives a steady glucose supply, which supports optimal growth and development.
Checking glucose is straightforward: prick your fingertip with a lancet, apply blood to a test strip, and read the result within seconds on your monitor. Most women alternate fingers to minimize discomfort. After a few days, the routine feels automatic rather than burdensome.
Complications to Watch For and When to Call Your Provider
Gestational diabetes treated with diet, exercise, and medication when needed is low-risk. However, certain symptoms warrant immediate contact with your provider to rule out complications. Contact your provider if you experience sudden blurred vision, severe headache, or upper abdominal pain. These symptoms can indicate preeclampsia, a pregnancy complication that occurs more frequently in gestational diabetes.
Preeclampsia is serious but treatable when identified early. Contact your provider if you develop unusual thirst, frequent urination, or persistent fatigue beyond typical pregnancy tiredness. While these can be normal in pregnancy, they may also signal that your glucose is not controlled adequately. Your provider checks your blood glucose and adjusts your management plan if needed.
If you have questions about your blood glucose log—such as why your fasting glucose is high despite careful eating, or why certain foods spike your glucose differently—contact your diabetes educator or provider. These conversations guide adjustments in medication, meal timing, or carbohydrate intake. Hypoglycemia (low blood glucose) is rare in gestational diabetes managed without insulin, but if you take insulin or metformin, discuss symptoms with your provider.
Shakiness, sweating, rapid heartbeat, and difficulty concentrating can signal low glucose. Keep glucose tablets or juice available and know how to treat low glucose if it occurs. After delivery, your glucose naturally returns to normal; this is not something you have failed to manage, but rather pregnancy hormones withdrawing. You do not need insulin or metformin after birth unless your provider advises otherwise. However, you have higher risk of developing type 2 diabetes later, so discuss long-term screening and prevention strategies with your provider.
Life After Gestational Diabetes Screening and Diagnosis
Once gestational diabetes screening is complete, whether your result is normal or positive, you return to your regular prenatal care schedule. If your screen was normal, you continue monthly visits and standard prenatal monitoring. If you were diagnosed, you maintain the more frequent visits and glucose monitoring until delivery. In the weeks before your due date, your provider discusses delivery plans.
Most people with gestational diabetes have vaginal deliveries without increased complication risk if glucose is controlled throughout pregnancy. Some providers recommend induction if your baby's ultrasound measurements suggest macrosomia, though this varies by individual circumstances and provider approach. After delivery, your baby's blood glucose is checked in the first hours of life to rule out neonatal hypoglycemia.
This is routine; most babies' glucose levels are normal. Your baby may stay near you during recovery rather than being separated for monitoring. You do not need postpartum glucose screening for gestational diabetes itself—the condition resolves once the placenta delivers and pregnancy hormones withdraw. However, you should have a fasting glucose or hemoglobin A1C check six to eight weeks after delivery or at your postpartum visit.
This establishes your baseline glucose now that you are not pregnant. Your healthcare provider discusses your diabetes risk going forward. Having had gestational diabetes increases your lifetime risk of type 2 diabetes to approximately 50%. You can reduce this risk by maintaining a healthy weight, staying physically active, eating a balanced diet with emphasis on whole grains and vegetables, and limiting sugary drinks.
If you plan another pregnancy, discuss preconception diabetes screening and prevention strategies. Gestational diabetes is not your fault. It results from how pregnancy hormones affect your body, not from diet choices before pregnancy or weight. Screening and management protected your baby during pregnancy. Moving forward, you have knowledge about your metabolic health that allows you to make informed choices for decades to come.
Frequently Asked Questions
Do I really need gestational diabetes screening if I feel fine?
Yes. Gestational diabetes often has no symptoms; you can feel completely healthy while blood glucose is elevated. Screening detects the condition early enough to prevent complications like excessive birth weight and birth injuries.
Can I eat or drink before my screening appointment?
It depends on which test you receive. The initial 50-gram nonfasting screen requires no fasting—you can eat normally. If you need the diagnostic 100-gram or one-step 75-gram test, you must fast for 12 hours beforehand.
What does it mean if my initial 50-gram screen is elevated?
It means you need a second, definitive test. About 75% of women with an elevated initial screen have normal results on the diagnostic test, so an elevated initial screen does not confirm gestational diabetes.
What is the difference between the two-step and one-step screening approaches?
The two-step approach uses a nonfasting 50-gram screen first, then a fasting 100-gram test if needed. The one-step approach uses a fasting 75-gram test only. Both are valid; your provider chooses based on their preference and your care setting.
If I'm diagnosed with gestational diabetes, does it mean I have diabetes permanently?
No. Gestational diabetes is temporary; it resolves after delivery when pregnancy hormones withdraw. However, having gestational diabetes increases your risk of type 2 diabetes later in life, so discuss prevention strategies with your provider.
How often do I check my blood glucose if I have gestational diabetes?
You typically check fasting glucose once daily (every morning) and glucose one to two hours after each meal. Most people check four to six times daily. Your provider or diabetes educator gives you specific targets for each check.
