A glucose test during pregnancy is a routine blood sugar screening that checks for gestational diabetes, a condition that develops only during pregnancy and affects how your body processes sugar. Most pregnant women take this test between 24 and 28 weeks, though your provider may recommend it earlier if you have certain risk factors. The test is simple, takes about an hour for the initial screen, and involves drinking a sweet glucose solution followed by a blood draw.
Why Pregnancy Requires a Glucose Test
During the second and third trimesters, the placenta produces hormones that make your cells less responsive to insulin. For most women, the body compensates by producing more insulin. But in some cases, blood sugar stays elevated, leading to gestational diabetes. This condition often causes no noticeable symptoms, which is exactly why screening is standard for virtually all pregnancies.
Uncontrolled blood sugar during pregnancy raises real risks. Babies are more likely to grow too large, which increases the chance of a cesarean delivery and birth complications. After birth, these babies face a higher risk of low blood sugar and, later in life, obesity and type 2 diabetes. For the mother, gestational diabetes increases the risk of preeclampsia and preterm birth. The good news is that once detected, it’s highly manageable, and most women go on to have healthy pregnancies.
Who Gets Tested Early
If you have a higher glucose level in your urine at a routine prenatal visit, or if you carry certain risk factors, your provider may screen you well before the standard 24 to 28 week window. Risk factors include a BMI of 30 or higher, a history of gestational diabetes in a previous pregnancy, polycystic ovary syndrome, being 35 or older, a previous baby who weighed more than 9 pounds at birth, or a family history of diabetes. Being Black, Hispanic, American Indian, or Asian American also increases risk. If none of these apply, you’ll typically be screened during the standard second-trimester window.
The Two-Step Testing Process
Most providers in the U.S. use a two-step approach. The first step is a quick screening test, and the second, if needed, is a longer diagnostic test.
Step 1: The One-Hour Glucose Challenge
You don’t need to fast for this one. At your appointment, you’ll drink a solution containing 50 grams of glucose. It’s very sweet, similar to flat soda, and comes in a few flavors like orange or lemon-lime. After drinking it, you wait one hour, then have your blood drawn. If your blood sugar comes back below the threshold your provider uses, you’re done. No further testing needed.
Some women feel nauseous, lightheaded, or jittery after drinking the solution. These side effects are temporary and usually pass within an hour or two. Eating a meal with protein before the test (since fasting isn’t required) can help reduce nausea.
Step 2: The Three-Hour Glucose Tolerance Test
If your one-hour result comes back above the cutoff, that doesn’t automatically mean you have gestational diabetes. It means you need the diagnostic follow-up. For this test, you fast overnight, then drink a more concentrated glucose solution. Your blood is drawn four times: once fasting, then at one, two, and three hours after the drink. Most guidelines require two or more of those four values to come back elevated before a gestational diabetes diagnosis is made. So even if one reading is high, you may still pass.
This test takes longer and can feel more uncomfortable since you’re fasting and sitting in the lab for three hours. Bring something to read, stay hydrated with water beforehand, and plan for a quiet morning.
What the Numbers Mean
For the one-hour screening, most providers use a cutoff of 130 or 140 mg/dL, depending on the practice. A result under that number is considered normal. For the three-hour diagnostic test, each blood draw has its own threshold, and your provider will compare your results against those cutoffs. A general reference: for a standard glucose tolerance test, blood sugar under 140 mg/dL at the two-hour mark is considered normal, 140 to 199 mg/dL falls into a prediabetic range, and 200 mg/dL or higher indicates diabetes. The specific numbers used for pregnancy screening may differ slightly from these general ranges, so your provider will interpret results in context.
What Happens If You’re Diagnosed
A gestational diabetes diagnosis can feel alarming, but the condition is very treatable. Your care team will start with two things: dietary changes and home blood sugar monitoring. You’ll learn to check your blood sugar several times a day using a finger-prick monitor, typically first thing in the morning and after meals. The dietary approach focuses on balancing carbohydrates with protein and fat, spacing meals evenly throughout the day, and choosing complex carbs over simple sugars.
For many women, these lifestyle adjustments are enough to keep blood sugar in a healthy range for the rest of pregnancy. If your numbers stay elevated despite dietary changes, your provider may add insulin or another medication. Depending on your situation, you might also be referred to an endocrinologist who specializes in blood sugar management during pregnancy. After delivery, gestational diabetes typically resolves, though you’ll be screened again postpartum since having it once increases your risk of developing type 2 diabetes later.
Alternatives to the Standard Glucose Drink
The standard glucose solution (often called Glucola) contains artificial dyes and flavoring that some women prefer to avoid. Several alternatives exist, though not all providers accept them, so check before your appointment.
- Dye-free Glucola: Same formulation without artificial coloring. Widely accepted and equally accurate.
- The Fresh Test: A commercially available alternative made with non-GMO cane sugar and real flavoring. Many OBs and midwives already recognize it.
- Jelly beans: About 28 jelly beans delivers roughly 50 grams of glucose. Some providers allow this as a substitute, though the exact sugar dose is harder to control.
- At-home blood sugar monitoring: Instead of a single drink-based test, some providers allow you to track your fasting and post-meal blood sugar at home over a week or longer. This gives a more realistic picture of daily blood sugar patterns.
- Hemoglobin A1c test: A simple blood draw that reflects your average blood sugar over the past two to three months. No sugary drink required, but it’s less commonly used as a standalone screen for gestational diabetes.
Food-based substitutes like orange juice, dates, or candy bars are occasionally allowed but harder to standardize. The key issue is delivering a precise dose of glucose so results are comparable to established reference ranges. If accuracy matters (and it does), stick with options your provider has approved.
Practical Tips for Test Day
For the one-hour screen, eat a balanced meal with protein a couple of hours before your appointment. Avoid loading up on sugary foods that morning, since a carb-heavy breakfast before the test can push your numbers higher than they’d otherwise be. Bring water, a snack for afterward, and something to keep you occupied during the wait.
For the three-hour test, you’ll need to fast for eight hours beforehand. Most women schedule this first thing in the morning so the fasting period overlaps with sleep. Pack a substantial snack or meal to eat immediately after your final blood draw, because you’ll likely feel shaky and hungry. Let your employer know in advance if you’ll need the morning off, since you’ll be at the lab for close to four hours by the time check-in and waiting are factored in.