Understanding the Gestational Diabetes Test: What to Expect

If you’re pregnant and have been told that you need to take a gestational diabetes test, it can be very overwhelming. You may have heard of the disease before and know some of its symptoms, but understanding what exactly is involved in testing for this condition—and why it's important—can give you peace of mind. There are also steps to take after the test results come back so that your pregnancy can be healthy and happy for both you and your baby. In this blog post, we'll explain everything about the gestational diabetes test so that expecting parents can feel informed about their care.


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What is Gestational Diabetes?

When a pregnant woman's body is unable to control the amount of glucose (sugar) in her blood, a condition known as gestational diabetes (or GDM) develops. Pregnancy hormones and weight gain are likely to blame for this, so you should feel better soon after giving birth. We know that type 2 diabetes occurs more frequently in women after they have had GDM, but this does not mean that you had diabetes before you conceived or that you will have diabetes after you give birth. That's why it's crucial to catch gestational diabetes early: it can cause issues for mom and baby like high birth weight, premature delivery, and even long-term health issues. The Centers for Disease Control and Prevention (CDC) estimates that between 2 and 10 percent of pregnant women will develop gestational diabetes. 

When to Test for Gestational Diabetes

If you're pregnant, it's important to get tested for gestational diabetes to ensure the health of both you and your baby. Typically, this glucose test is done between 24 and 28 weeks of pregnancy. However, if you have a family history of diabetes or have previously been diagnosed as prediabetic, your healthcare provider may recommend getting tested sooner. While the thought of having gestational diabetes may be daunting, it's important to note that managing it can reduce the risk of complications for both you and your baby.


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Types of Gestational Diabetes Tests

There are two common strategies for evaluating gestational diabetes— the “one-step” strategy and the “two-step” strategy. The tests involve extracting blood before and after the patient drinks a sugary glucose drink. Both of the tests are essentially identical, but they vary in the amount of blood drawn, the amount of fasting required, and their duration. While the approach recommended by your physician will depend on their preferences, the ultimate goal for the test is to keep you and your baby healthy while also identifying potential risks, so rest assured that your care team has your family’s best interests in mind.

One-Step Strategy

  1. First, you need to go without food for at least eight hours.
  2. A blood sample is taken to determine your fasting blood sugar level.
  3. You will consume 75 grams of a sugary glucose solution similar to Gatorade.
  4. Wait an hour (you'll probably be asked to wait in the clinic's waiting room so staff can observe you;
  5. A second blood sample is taken an hour after the patient has consumed the glucose solution to determine the level of glucose in the blood.
  6. Wait an extra hour
  7. A third blood sample is taken 2 hours after ingesting the glucose solution (or 1 hour after the previous blood test).

When one or more of the following blood glucose levels is equal to or higher than these thresholds, a diagnosis of gestational diabetes is made:


  • Fasting: 92 mg/dL
  • 1 hour: 180 mg/dL
  • 2 hours: 153 mg/dL

Two-Step Strategy

The first step (the "glucose challenge test" or "one-hour glucose tolerance test"):

  1. There is no need to fast.  
  2. Taking blood for the first time is optional.
  3. The 50 grams of glucose solution will be ingested.
  4. Hold off for an hour
  5. After an hour of drinking the glucose solution, your blood sugar will be tested. Results of 130, 135, or 140 mg/dL suggest proceeding to Step 2. It's important to remember that different pregnancy doctors may use different Step 1 results.

Second, there is what is known as a "glucose tolerance test" or a "three-hour test."

  1. Take an eight-hour fasting break
  2. Fasting blood sugar levels are measured after the initial blood draw.
  3. One hundred grams of the glucose solution will be ingested.
  4. In this step, blood is drawn one hour, two hours, and three hours after ingesting the glucose solution (yes, you'll get poked four times total; once after fasting, and three times after ingesting the glucose solution; all of this after going without food for 11 hours).

Keep in mind that some doctors will diagnose GDM if only one blood glucose value is equal to or higher than these numbers; a diagnosis of GDM requires at least two of the following blood glucose values to be equal to or higher than these:


  • Fasting: 95 mg/dL
  • One hour: 180 mg/dL
  • Two hours: 155 mg/dL
  • Three hours: 140 mg/dL

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What to Eat Before your Gestational Diabetes Test

a person holding a glucose meter


Eating before the gestational diabetes test can be a bit tricky, but it’s important to make sure you and your baby are well taken care of during this time. If you’re told to fast for the test, it’s essential to refrain from eating for at least eight hours beforehand. This can be challenging, but it’s necessary to get accurate results. If you’re not instructed to fast, it’s best to stick to your regular diet leading up to the test. This ensures that your initial blood draw reflects your typical eating habits. Regardless of what you eat or how long you fast, remember that the test is necessary for the health of both you and your baby. It may not be the most enjoyable experience, but it’s a small price to pay for ensuring a safe and healthy pregnancy.

Passing the Test

a pregnant woman holding her stomach


How to pass the gestational diabetes test is a common concern among expecting mothers. However, the reality is that there is no passing or failing this test. It simply reveals whether or not you are diabetic. While some may be tempted to cheat the system, doing so could have negative consequences for both you and your baby. If you do have diabetes, it's important that you receive the treatment you need to prevent potential problems. On the other hand, if you don't have diabetes, you can rest easy knowing that you've passed the test and can focus on caring for yourself and your growing baby.


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Testing for Gestational Diabetes

The Gestational Diabetes Test is a crucial test that is performed during pregnancy to ensure the well-being of both the mother and the baby. By understanding what the test entails and what to expect during the test, you can prepare yourself mentally and physically for this test. Be sure to follow your healthcare provider's instructions carefully and reach out to them if you have any concerns or questions. Together, you can work towards a healthy pregnancy and a healthy baby!


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