No, not for the 1-hour pregnancy glucose screen; fasting is required for the longer diagnostic tolerance test.
Glucose checks in pregnancy come in two flavors. The quick screening uses a 50-gram drink and a single blood draw one hour later. The longer diagnostic visit (often called an oral glucose tolerance test, or OGTT) includes fasting, a larger drink, and several blood draws over two to three hours. Knowing which visit you’re booked for helps you prepare the right way and avoid repeat trips.
What Each Test Is And Why It’s Ordered
Most clinics start with a one-hour screen during weeks 24–28. It’s a quick check to see how your body handles sugar during pregnancy. If that screen lands above the lab’s cut point, the next step is a longer tolerance test to confirm or rule out a diagnosis. Some practices use a single 75-gram, two-hour visit that both screens and diagnoses on the same day. Policies vary by country and by clinic, so check your appointment type.
Fast Or Not? The Short Version
No fasting is needed for the one-hour screen. Fasting is needed for the diagnostic OGTT (whether that’s a two-hour 75-gram test or a three-hour 100-gram test). During the test window you’ll skip food, flavored drinks, gum, and nicotine; plain water is allowed unless your lab states otherwise.
Test Types At A Glance
| Test Type | Fasting Needed? | Typical Timing |
|---|---|---|
| 50-g One-Hour Screen (GCT) | No | Blood draw 1 hour after the drink |
| 75-g Two-Hour OGTT | Yes (8–12 hours) | Fasting draw, then at 1 and 2 hours |
| 100-g Three-Hour OGTT | Yes (8–12 hours) | Fasting draw, then at 1, 2, and 3 hours |
Fasting Rules For Pregnancy Sugar Screening
For the one-hour screen, eat and drink as you normally would before the visit. Once you drink the solution, you’ll wait on site until the blood draw; only water is allowed during that hour. The longer tolerance tests require an overnight fast. Most labs ask you to stop food at bedtime and come in early. You’ll have a fasting blood draw, drink the glucose solution, and then stay seated for the remaining draws.
Why The Rules Differ
The screening drink is a quick challenge designed to be simple and convenient. The diagnostic visit needs a steady starting point to read your body’s response across several time points; that’s why it starts with a fasting sample. These setups are described in sources like the Mayo Clinic glucose challenge test page and in the ADA pregnancy care standards.
How To Prepare Based On Your Appointment
Booked For The One-Hour Screen
- Eat normally beforehand. A balanced meal a few hours before the visit helps you feel steady during the hour wait.
- Once you drink the solution, stick to sips of water only until the blood draw.
- Plan for about 60–90 minutes at the lab or clinic from check-in to wrap-up.
Booked For A Diagnostic OGTT
- Stop food overnight; most labs want 8–12 hours with water only.
- Take morning meds as your clinician advises. If you’re unsure, ask the office when they confirm the appointment.
- A morning slot helps keep the fast shorter and reduces nausea from an empty stomach.
What To Expect During Each Visit
During The One-Hour Screen
Staff will hand you a premeasured 50-gram glucose drink. You’ll finish it in one sitting. Then you’ll wait on a chair in the lab area; many clinics ask you to stay put to keep activity level even. After 60 minutes, they’ll draw one tube of blood from a vein.
During The Two-Hour Or Three-Hour OGTT
First is a fasting blood draw. Then you’ll drink either a 75-gram or 100-gram solution. Blood draws follow at set intervals. You’ll need to remain on site, avoid walking laps, and keep only water by your side. Bring a book, headphones, or a show; the time passes faster with a plan.
What To Eat The Day Before
For a non-fasting screen, a normal day of meals is fine. Many clinics suggest a balanced plate with carbs, protein, and fiber in the preceding meals. For a fasting OGTT, focus on a regular dinner and stop food at the time your lab recommends. Water overnight keeps you hydrated and can make blood draws easier.
If You Feel Queasy With Sweet Drinks
Nausea can happen, especially with the stronger solutions. Small, slow sips help. Ask for the drink chilled if available. If vomiting occurs, tell staff right away; they’ll advise whether the test needs to be rescheduled.
Timing, Work, And Childcare
The one-hour visit fits into a lunch break for many people. The diagnostic visit takes longer; budget two to three hours plus check-in. If you have childcare or work shifts to juggle, book an early morning slot and let your manager know the expected window.
Medications, Supplements, And Special Cases
Certain medicines can raise glucose levels. Steroids and some antipsychotics are common examples. Don’t stop a prescribed drug without a plan; ask the clinic team whether any changes are needed for test day. People with prior surgery on the stomach or intestines sometimes absorb the drink fast and can feel dizzy; let staff know your history so they can seat you near the draw chair and check in during the wait.
Understanding Results At A High Level
Labs use different cut points. A screen above the local threshold triggers the longer visit. Diagnosis relies on set values at the fasting draw and at one or more time points during the OGTT window. National groups describe these steps in plain language; the USPSTF page on screening explains the staged approach.
Single-Visit Versus Two-Step Approaches
Some clinics use a one-step method: a 75-gram, two-hour visit that starts with a fasting draw and then two timed draws after the drink. Others use a two-step path: a non-fasting one-hour screen first, then a three-hour OGTT if the screen is above the cutoff. Both systems aim for reliable results while balancing time and convenience. If your paperwork lists a 75-gram drink and two-hour stay, plan for fasting. If it lists a 50-gram drink and one-hour wait, no fasting is needed.
Comfort Strategies For Test Day
Before You Go
- Wear a short-sleeve top or layers to make venipuncture easier.
- Drink water during the drive to the lab.
- Bring a snack for after the final draw, especially if you’ve fasted.
During The Visit
- Stay seated and calm; light scrolling or reading is fine.
- Use the restroom right before the clock starts; leaving the chair can delay the scheduled draw.
- Tell staff if you feel light-headed so they can recline the chair or add a cold pack.
Common Questions People Ask
Can I Drink Coffee Before The One-Hour Screen?
Black coffee can nudge glucose and heart rate. Most labs prefer water only after you arrive and drink the solution. If you’re sensitive to caffeine, skip it that morning.
Can I Nurse Or Pump During The Wait?
Lactation increases energy use and can shift glucose. Ask your lab whether a quick pump break fits the timing; if so, keep activity light and return to the chair promptly.
What If I Ate Close To My Appointment?
For the one-hour screen that’s usually fine. If you’re booked for an OGTT and ate within the fasting window, tell the desk; they’ll guide next steps.
When The Clinic Screens Earlier Than Usual
People with higher risk may be checked earlier in pregnancy. If the early check is a full OGTT, fasting is required. If it’s a quick screen, no fasting. The plan depends on your history and the practice’s protocol.
After The Draws: What Happens Next
Results often post to your portal within a day or two. If you passed the screen, your prenatal routine continues as planned. If you head to the diagnostic visit next, use the prep steps above. When a diagnosis is made, your team will set up nutrition teaching, a glucose meter, and follow-up visits. The aim is steady numbers so you and your baby stay well.
Quick Planner For Each Scenario
| Scenario | What To Do | Why It Helps |
|---|---|---|
| One-Hour Screen | Eat normally; water during the hour wait | Reduces nausea; keeps the process simple |
| Two-Hour 75-g OGTT | Overnight fast; arrive early; bring a snack for after | Gives a steady baseline and smooth recovery |
| Three-Hour 100-g OGTT | Overnight fast; plan for a longer chair stay | Captures extra time points for diagnosis |
Key Takeaways You Can Act On Today
- No fasting for the one-hour screen; fasting for diagnostic tolerance tests.
- Confirm your appointment type when scheduling so prep matches the visit.
- Bring water, a good snack for the ride home, and something to read.
Trusted Sources You Can Check
For clear step-by-step descriptions of the one-hour screen and the longer tolerance tests, see the Mayo Clinic page for the screen and the ADA standards for pregnancy care. The USPSTF recommendation also outlines testing steps used across clinics.