50g and 75g Glucose Challenge Test (GCT) During Pregnancy
Last updated on May 30th, 2025 at 01:20 pm
If you’re expecting a baby, you’ve probably heard about the glucose challenge test, a routine screening that checks for gestational diabetes. This simple test ensures your body is handling sugar properly, keeping both you and your baby healthy. But what exactly is it, and how do you prepare for it? Let’s break it down in simple terms.
What Is the Glucose Challenge Test?
The glucose challenge test (sometimes called the one-hour glucose challenge test) is a quick and easy way to check how your body processes sugar during pregnancy. It helps detect gestational diabetes ( a type of diabetes that develops only during pregnancy) and measures how your body uses insulin during pregnancy.
Most women take this test between 24 and 28 weeks of pregnancy, but if you have risk factors – like a high BMI, a history of diabetes, or PCOS – your doctor might recommend testing earlier.
Types of Glucose Challenge Tests
There are two types of glucose challenge tests, which differ in procedure and glucose amount: the 50g glucose challenge test and the 75g glucose challenge test.
1. 50g Glucose Challenge Test (One-Hour Test)
- No fasting is required before the test.
- You’ll drink 50 grams of glucose within 5 minutes.
- After one hour, a blood sample is taken.
- If your blood sugar is 140 mg/dL (7.8 mmol/L) or higher, you’ll need a follow-up glucose tolerance test.
2. 75g Glucose Challenge Test (Two-Hour Test)
- You must fast (no food or drinks except water) for at least 8-12 hours before the test.
- A fasting blood sample is taken first.
- You’ll drink 75 grams of glucose within 5 minutes.
- Blood samples are collected at 1 hour and 2 hours post-drink.
- If your results show higher-than-normal blood sugar at any stage, you may be diagnosed with gestational diabetes.
Difference Between Oral Glucose Tolerance Test (OGTT) and Glucose Challenge Test (GCT)
Many people confuse these two tests, but here’s the key difference:
- The GCT is a screening test.
- The OGTT is a follow-up diagnostic test.
- The GCT doesn’t need fasting; the OGTT does.
| Test | Purpose | Glucose Amount | Fasting Required? | Duration |
|---|---|---|---|---|
| Glucose Challenge Test (GCT) | Screening for gestational diabetes | 50g (1-hour test) Or 75g (2-hour test) |
| 1-2 hours |
| Glucose Tolerance Test (GTT) | Diagnostic test for gestational diabetes | 100g (3-hour test) |
| 3+ hours |
How to Prepare for the Glucose Challenge Test
Both the 50g and 75g glucose challenge test has different preparation procedures. Here’s how:
| Test | Preparation |
|---|---|
| For the 50g Glucose Challenge Test (One-Hour Test): |
|
| For the 75g Glucose Challenge Test (Two-Hour Test): |
|
| For the 100g Glucose Tolerance Test (If Needed): |
|
What Happens During the Test?
- Step 1: Fasting Blood Draw (only for 75g and 100g tests)
- A technician will take a fasting blood sample to measure your baseline blood sugar.
- Step 2: Drink the Glucose Solution
- You’ll be given a sweet glucose drink, similar to a flat soda.
- For the 50g test, you drink 50 grams of glucose.
- For the 75g test, you drink 75 grams of glucose.
- For the 100g test, you drink 100 grams of glucose.
- You must drink it within 5 minutes.
- Step 3: Blood Draws at Set Intervals
- 50g Test: Blood is drawn 1 hour after the initial draw.
- 75g Test: Blood is drawn 1 and 2 hours later.
- 100g Test: Blood is drawn 1, 2, and 3 hours after the initial draw.
- Step 4: Resume Normal Activities
- After the test, you can eat and drink as usual.
- Your doctor will inform you if further testing is needed.
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What Do the Results Mean?
The normal glucose tolerance test results should be as follows:
| Test Type | Fasting | 1 Hour | 2 Hours | 3 Hours |
|---|---|---|---|---|
| 50g GCT | N/A | Below 140 mg/dL | N/A | N/A |
| 75g GTT | Below 92 mg/dL | Below 180 mg/dL | Below 153 mg/dL | N/A |
| 100g GTT | Below 95 mg/dL | Below 180 mg/dL | Below 155 mg/dL | Below 140 mg/dL |
What If You Fail the Test?
- If one value is high, your doctor may recommend diet changes and a retest.
- If two or more values are high, you will be diagnosed with gestational diabetes and need blood sugar monitoring, dietary changes, and possibly insulin.
Managing Gestational Diabetes
If diagnosed, don’t panic! Many women successfully manage gestational diabetes through:
- Balanced diet (fewer processed carbs, more protein, and fibre).
- Regular exercise (such as walking or prenatal yoga).
- Blood sugar monitoring with a glucose meter.
- Insulin or medication if needed.
Final Thoughts
The glucose challenge test during pregnancy is a simple but essential part of prenatal care. Whether you take the 50g one-hour test or the 75g two-hour test, this screening ensures that you and your baby stay healthy. If your results are high, don’t stress; talk to your doctor, as gestational diabetes can be managed with the right care.
Clinic One specializes in thorough glucose testing to catch gestational diabetes and keep your pregnancy on track. Known for our patient-centred care, advanced lab facilities, and an experienced team of OB/GYN professionals, we ensure a comfortable and thorough testing experience.
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FAQs
What is the difference between GCT and OGTT?
The GCT is a screening test that checks how your body handles sugar and usually involves drinking 50g of glucose without fasting. If your results are high, you may need the OGTT, which is a more detailed, diagnostic test requiring fasting and multiple blood draws after consuming a higher glucose amount (75g or 100g).
What is a 75g oral glucose challenge test?
The 75g Oral Glucose Challenge Test is a two-hour test used to screen or diagnose gestational diabetes. After fasting for 8-12 hours, your blood is drawn, and you drink a solution containing 75g of glucose. Your blood is then tested again at 1 and 2 hours to measure how your body processes sugar.
When is a GCT test done in pregnancy?
The GCT is typically done between 24 and 28 weeks of pregnancy. If you have risk factors like a high BMI, a history of gestational diabetes, or PCOS, your doctor may recommend taking it earlier.
Can I refuse the glucose test when pregnant?
Yes, you can refuse the test, but it’s important to talk with your healthcare provider first. They may suggest alternative monitoring or explain the risks of missing a potential gestational diabetes diagnosis, which can impact both you and your baby’s health.
What are the signs you passed your glucose test?
A result below 140 mg/dL is typically considered normal. To pass the test, your results should be lower than this. If your number is higher, you may need follow-up testing, but your doctor will guide you through the next steps.
