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What Should You Eat Before a Pregnancy Glucose Tolerance Test?

It's essential you prepare for a pregnancy glucose test to get accurate results!
What Should You Eat Before a Pregnancy Glucose Tolerance Test?
Updated: November 16, 2023
Medically reviewed by  Tina Hayes, MSN, RN, RNC-OB

Are you worried about gestational diabetes and wondering how to pass the pregnancy glucose test? Luckily, there are a few things you can do to help get accurate results and avoid false positives.

During the second trimester of pregnancy, women take a routine diabetes test that helps determine if they have gestational diabetes. Knowing what you should eat before a pregnancy glucose test is important because food does affect blood glucose levels.

What is a Pregnancy Glucose Tolerance Test? 

What is a Pregnancy Glucose Tolerance Test? 

A glucose test is a test that measures how well a person’s body can absorb glucose when he/she is given a specific amount of sugar. The pregnancy glucose test is a routine screening that tests for gestational diabetes in pregnant women since pregnancy can cause type 2 diabetes. The screening is done during the second trimester between 24 and 28 weeks of pregnancy.

There are two different types of glucose screenings. They include the glucose challenge test and the 3-hour glucose tolerance test.

The Glucose Challenge Test 

When taking the one-hour glucose challenge test, you are given a drink called glucola, a sweet glucose solution containing 50 grams of sugar. After one hour of drinking it, the doctor will take a blood sample and measure your blood sugar levels. You have passed if the blood draw results are below 140 mg/dl. If your blood sugar is over 190 mg/dl after the one-hour test, you will be diagnosed with gestational diabetes (GD). If the results are in between, you will need to take the oral glucose tolerance test.

Oral Glucose Tolerance Test (OGTT) 

This three-hour screening involves drinking a sugary drink containing 75 grams of glucose. The doctor will take a blood sample before drinking the solution and again three more times every hour following.  All the blood level results need to be normal to pass this screening. If one is abnormal, you can make simple changes to your diet. If two or more are abnormal, you have GD.

According to the American Pregnancy Association, the following levels are considered abnormal: 

Fasting Glucose Level: 95 mg/dl or higher

One Hour Level: 180 mg/dl or higher

Two Hours Level: 155 mg/dl or higher

Three Hours Level: 140 mg/dl or higher

What Foods Should You Eat Before a Glucose Test?

What Foods Should You Eat before a Glucose Test?

Foods can affect the glucose challenge test. When you eat, your body converts the carbs into glucose. If you eat the wrong types of food right before the glucose screening, you may get a false result for gestational diabetes.

Any food that is a complex carbohydrate is great to eat before this screening test because your body breaks them down slowly, and these foods do not cause a spike in sugar. Here are some examples of complex carbs you may want to eat:

  • Whole Grains (whole wheat bread, brown rice)
  • Legumes (chickpeas, lentils, black beans)
  • Fresh fruit
  • Non-starchy veggies
  • Dairy
  • Nuts & nut butter
  • Fish
  • Lean meats

Usually, the provider schedules the test in the morning, so you should eat a proper breakfast. The best breakfast would be a combination of complex carbohydrates and protein. Some examples include whole wheat toast with avocado, greek yogurt with fruit, and scrambled eggs with tomatoes.

In contrast, the OGTT comes with different instructions. You should eat 150g of carbs for three days before this test. According to the National Institute of Diabetes and Digestive and Kidney Diseases, you should stop eating or drinking anything for at least 8 hours before this screening. You can take sips of water.

What Not to Eat Before a Glucose Screening Test 

What Not to Eat before a Glucose Screening Test

You should not eat foods high in sugar for the one-hour test. These types of food are easily digested and cause high blood sugar levels. Here are some foods to avoid for the challenge test: 

  • Fruit juices, smoothies & soda
  • Sweet tea
  • Granola 
  • Refined cereals
  • Pancakes
  • Donuts
  • White bread 
  • Croissants
  • Muffins
  • Refined grains

In contrast, as mentioned before, you should not eat or drink anything for at least 8 hours before the OGTT. You should also not eat low carbohydrate meals during the three days before the OGTT.

What are the Benefits of Eating Before a Glucose Pregnancy Test? 

Many women think that they have to fast before a glucose challenge test. In reality, you should eat before this screening because not eating would cause abnormal insulin levels.

For the OGTT, you must eat a diet with high carbohydrates for three days before the test. Eating a low carbohydrate or restrictive diet before this screening can cause problems in insulin levels, and you may even get a false positive for gestational diabetes. The benefit of eating 150 grams of carbohydrates for three days is that it helps keep insulin sensitivity regular and helps prepare your metabolism for tolerating the glucose drink given during the test.

What Happens If You Do Not Pass the Glucose Screening Test? 

If you do not pass the glucose challenge test, that does not mean you have gestational diabetes. It just means you will have to take the three-hour test. However, if you still get abnormal test results in two or more blood samples, you will likely be diagnosed with gestational diabetes.

Your provider will monitor you more if you have gestational diabetes. Your doctor and nutritionist will probably put you on a specific diet to help keep your insulin levels steady. Luckily, gestational diabetes usually goes away after the birth of your baby.

Gestational Diabetes 

Gestational Diabetes


Gestational diabetes occurs when the pancreas does not make enough insulin to keep glucose blood levels regular during pregnancy. This usually happens because pregnancy hormones can affect the production of insulin.

Some women have higher risks of developing gestational diabetes. These risk factors include having a family history of diabetes, excess weight, pre-diabetes, gestational diabetes during prior pregnancies, and high blood pressure.

If you have risk factors for GD, your doctor may skip the one-hour test and recommend the OGTT from the start. Gestational diabetes can cause pregnancies to be more difficult. Your baby has a higher risk of being larger than the average size, being born premature, and having a higher risk for type 2 diabetes in the future.

You should eat a balanced diet and follow your doctor’s instructions. Routine prenatal appointments are even more important to attend if you have GD.

In Conclusion 

Blood glucose levels are measured during the second trimester of pregnancy to help detect gestational diabetes mellitus. Two screenings are used during pregnancy to detect diabetes. The food you eat can affect the results. Knowing what to eat before the glucose tests is important to get accurate results. Speak to your healthcare provider before the test if you have concerns or questions.

Sources +

American Pregnancy. Glucose tolerance test.

National Institute of Diabetes and Digestive and Kidney Diseases. Tests and diagnosis for gestational diabetes.

Halimeh Salem

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