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  • Also Known As:
  • Glucose Challenge Test
  • Oral Glucose Challenge Test
  • OGCT
  • Glucose Tolerance Test
  • Oral Glucose Tolerance Test
  • OGTT
  • Glucose Screening Test
  • 2-Hour Glucose Tolerance Test
  • 3-Hour Glucose Tolerance Test
  • Glucose Loading Test
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Gestational diabetes is a type of diabetes that begins during pregnancy. Diabetes is a serious health condition that can develop when too much glucose, a type of sugar, is present in the bloodstream.

Hormone changes during pregnancy can interfere with the way the body uses glucose. These changes and other factors such as weight, age, and ethnicity can increase the risk of gestational diabetes.

Developing diabetes during pregnancy poses health risks to both the parent and child. It is also associated with an increased chance of developing diabetes later in life.

Gestational diabetes is diagnosed with blood tests that show how well the body uses glucose. The tests are usually performed during the second trimester of pregnancy when gestational diabetes is most likely to occur.

About the Test

Purpose of the tests

The purpose of gestational diabetes testing is to identify diabetes that develops during pregnancy.

Gestational diabetes often does not cause any noticeable symptoms at first. Diagnosing gestational diabetes before it causes symptoms or complications during pregnancy can help you and your doctors manage the condition in order to improve your health and the health of your baby.

What do the tests measure?

Glucose tests for gestational diabetes measure blood sugar levels under controlled conditions. The tests provide a picture of how well your body is able to metabolize glucose during your pregnancy.

There are two main ways to conduct a glucose test for gestational diabetes: the two-step test and the one-step test. In the United States, the two-step test is more commonly used.

Two-step test

The two-step glucose test can involve one or two sessions, depending on the results of the first step.

Step one of a two-step test is also called a glucose challenge test or glucose screening test. In step one, you will drink a solution with glucose and then have your blood glucose levels checked after one hour. If your blood glucose level is within the range expected for healthy people, your testing will be complete, and you will not need to perform step two. If your blood glucose level is higher than normal, you will need to return for step two.

Step two is called a glucose tolerance test or oral glucose tolerance test, and it is administered over three hours. For this test, you will need to go without eating or drinking anything but water for eight hours prior to the test. The glucose tolerance test begins with a blood draw to determine your baseline glucose level. Next, you will drink a solution containing even more glucose than in the solution from step one. Afterward, you will have three additional blood draws that are taken once per hour over three hours. Each blood sample will be tested for its glucose level.

One-step test

The one-step glucose test may also be referred to as an oral glucose tolerance test. For the one-step test, you must not eat or drink anything but water for eight hours beforehand. The one-step test begins with a baseline blood draw. Then you will drink a glucose solution, and your blood will be tested after one hour has passed and then again another hour later. Each sample will be analyzed to determine its glucose level.

The one-step test is done in one appointment that usually lasts about two hours.

When should I get a glucose test for gestational diabetes?

Gestational diabetes testing is offered between the 24th and 28th weeks of pregnancy.

Your doctor may recommend that you get tested sooner if you have an increased risk of developing gestational diabetes. Some of the risk factors for this condition include:

  • Becoming pregnant after the age of 25
  • Being overweight before becoming pregnant or gaining a large amount of weight during pregnancy
  • Having family members with diabetes
  • Having prediabetes, which is an elevated level of blood glucose that can lead to diabetes
  • Having had gestational diabetes during a previous pregnancy
  • Belonging to certain racial or ethnic groups, including people who are Black or African American, American Indian or Native American, Latino/Latina, Asian, or Pacific Islander
  • Previously giving birth to a baby who weighed 9 pounds or more
  • Having a hormonal condition called polycystic ovary syndrome
  • Having high blood pressure
  • Having a large amount of amniotic fluid, which is the fluid that surrounds the baby in the uterus

You can discuss your risk factors and chance of gestational diabetes with your doctor. Your doctor will be able to advise you on the timing and appropriateness of testing in your specific situation.

Finding a Glucose Test for Gestational Diabetes

How to get tested

Your primary care provider or doctor providing prenatal care is generally the one to order a glucose test for gestational diabetes. The test may be conducted in your doctor’s office, a clinic, or a hospital.

Can I take the tests at home?

There are no at-home versions of gestational diabetes glucose tests. These tests require sample collection and analysis by trained professionals in a clinical setting over the course of several hours.

How much do the tests cost?

The cost of gestational diabetes testing may depend on which type of test your doctor orders for you and the facility where the test is performed. The complete cost can include fees charged by your doctor for office visits and by the laboratory for labor and the analysis of your samples.

If you have health care coverage, your insurance provider will usually cover these costs in part or in full. Copayments and deductibles, however, may be your responsibility to cover. You may wish to discuss costs with the billing staff of your doctor’s office or the laboratory that conducts the test. A representative from your insurance company may be able to share additional information with you about potential out-of-pocket costs.

Taking a Glucose Test for Gestational Diabetes

Glucose tests for gestational diabetes may involve either one or two appointments that can take between one and three hours each. Each test requires blood samples taken from a vein and involves drinking a sweetened drink.

Before the test

Your preparations may depend on whether you take the two-step or one-step glucose test.

For the first step of a two-step test, you will not have any special preparations beforehand. You can eat and drink as usual prior to the test.

If you need to return for the second step, you will have to fast for at least eight hours beforehand. This means you will need to go without eating or drinking anything besides water. Fasting glucose tests are often done in the morning, so most of your fast can be overnight while you sleep.

If you are taking the one-step test, you will need to fast for at least eight hours before your appointment.

Be sure to talk to your doctor about any medications you may be taking in case they may interfere with the test results. Carefully follow any pre-test instructions from your doctor, including any specific directions about how long to fast before the test.

During the test

For each of the glucose tests, you will need one or more blood draws conducted by a phlebotomist, who is a health professional trained to collect blood samples.

With each blood draw, the phlebotomist will clean the skin where the sample will be taken, often on the underside of your elbow. The phlebotomist may tie a band called a tourniquet around your upper arm to increase the blood in the vein. Then the phlebotomist will insert a thin, hollow needle through the skin into the vein. Your blood sample will flow through the needle and collect in an attached tube.

It’s normal to experience a slight pain or stinging when the needle is inserted into the vein or withdrawn from the arm.

For each test session, you will need to drink a glucose-containing drink. These drinks taste sweet. The drink will have a different amount of glucose depending on the type and step of the test.

The order in which you receive blood draws and drink the beverage also depends on the test:

  • In step one of a two-step test, you will have just one blood draw an hour after you drink the solution.
  • In step two of a two-step test, you will have four blood draws in total, each an hour apart. The first blood draw will happen before you drink the solution, and then you will have three more blood samples taken over the next three hours.
  • For a one-step test, you will have three blood draws. One will happen before you drink the solution, another an hour afterward, and one more after another hour.

After the test

After drawing your blood, the phlebotomist will apply a small bandage over each site where the blood was taken. You can usually remove the bandage after a couple of minutes, but you may want to leave it in place for an hour or more.

Serious side effects from glucose blood tests are rare. You may notice some pain or bruising in your arm where the phlebotomist drew your blood. Some people find that drinking the glucose solution upsets their stomachs, makes them slightly dizzy, or causes them to sweat.

If you were required to fast before your test, you can eat after the test is done. You may want to have a snack on hand to eat after your final blood draw is complete.

Most of the time, you can continue with your usual activities after you’ve finished the test.

Glucose Test Results

Receiving test results

The results of your blood glucose tests may be available soon after they are conducted, or it may take several business days for the lab to process your samples. The time it takes can depend on which test has been ordered and where the test is conducted.

You may be able to access your results through an online portal, or they may be mailed to you. Your doctor may want to have another appointment to go over your results. You may also be able to discuss the results  over the phone or through secure electronic messaging with your doctor.

Interpreting test results

Glucose test results are often reported in milligrams per deciliter, or mg/dL. They may also be displayed in millimoles per liter, or mmol/L.

You may see reference ranges included with your gestational diabetes test results. These show the upper and/or lower limits of blood glucose values that may be seen in healthy individuals. Reference ranges may be different depending on the method used to analyze the sample and the laboratory where the analysis is performed.

If you take a two-step test and have two or more elevated blood glucose levels, you may have gestational diabetes. If you take a one-step test and have one or more elevated blood glucose levels, you may have gestational diabetes.

It’s important to talk to your doctor about how your test results fit into your overall health picture. Your doctor may be able to answer questions about the reference ranges used, explain the possible causes behind your blood glucose values, and recommend further tests or treatments as needed.

Are test results accurate?

Glucose testing for gestational diabetes is a routine part of pregnancy care and is largely accurate. But as with all medical testing, these tests are not perfect. Laboratories must carefully follow protocols to produce reliable results. You must also closely follow pre-test instructions in order for the test to be reliable.

When you go over your test results with your doctor, you may want to ask about the method used to analyze your blood samples, the reference range for this method, and the overall dependability of the test results.

Do I need follow-up tests?

In some cases, your doctor may want you to repeat the test if only one of your blood draws showed an elevated glucose level. Your doctor may order the repeat test after you make changes to your diet to determine whether those changes were beneficial.

If your results indicate that you have gestational diabetes, you and your health care providers will need to keep track of your blood glucose levels for the remainder of your pregnancy. Your doctor may ask you to do this at home by regularly pricking your finger tip with a very small needle and testing the blood droplet with a home glucose meter.

Because uncontrolled gestational diabetes can heighten the risk of complications during pregnancy, your doctor will carefully monitor both your and your baby’s health during the rest of your pregnancy.

Although most cases of gestational diabetes resolve after childbirth, having diabetes while pregnant is associated with an increased risk of developing type 2 diabetes in the years following your pregnancy. If you are diagnosed with gestational diabetes, it is recommended that you get tested for type 2 diabetes between one to three months after you give birth and that you have glucose testing again every one to three years.

Questions for your doctor about test results

When you talk to your doctor about the results of your glucose test, the following questions may be helpful to ask:

  • What are the results of my test?
  • Will I need to repeat this test or take another test to confirm the results?
  • What do these results mean for my health and my baby’s health?
  • What changes to my lifestyle, if any, do you recommend based on my test results?
  • Will I need to monitor my blood glucose levels for the rest of my pregnancy?
  • Will I need to take any medications because of my results?

Related Tests

Glucose tests for gestational diabetes vs. other types of diabetes

The glucose tolerance test is also used outside of pregnancy to diagnose type 2 diabetes. However, when testing non-pregnant individuals, the reference ranges are different. Generally, gestational diabetes can be diagnosed with lower blood glucose levels than those required to diagnose type 2 diabetes.

Glucose tests for gestational diabetes vs. hemoglobin A1c testing

The hemoglobin A1c test is frequently used to detect or monitor diabetes in other contexts. Some doctors prescribe the hemoglobin A1c test early in pregnancy to check for undiagnosed prediabetes or type 2 diabetes; however, it is not recommended as a stand-alone test for gestational diabetes.

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