What to Expect From Gestational Diabetes Testing

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If you are pregnant, your obstetrician has probably told you that you will need gestational diabetes testing. Don't worry—gestational diabetes testing is an important part of routine prenatal care. Most women are tested during weeks 24 through 28 of pregnancy. If you have any risk factors for diabetes, your doctor may consider testing your blood sugar as early as your first prenatal visit.

Purpose of Test

Certain hormones increase during pregnancy, transferring valuable nutrients from the mother to the baby so that the fetus develops and grows. Other hormones block the action of insulin, ensuring that the mother herself does not develop low blood sugar. To compensate, the mother’s insulin levels rise.

If her insulin levels cannot increase sufficiently, rising blood sugar levels will eventually result in gestational diabetes. Untreated, gestational diabetes can lead to complications for both the mother and the baby. These complications may include:

  • Macrosomia (oversized baby)
  • Increased chance of cesarean section delivery
  • High blood pressure during pregnancy
  • Low blood sugar (hypoglycemia) in the baby immediately after delivery
  • Stillbirth
  • For the child, risk of obesity and developing type 2 diabetes later in life

Many pregnant women who develop gestational diabetes have no risk factors, but in others, risk factors may include:

  • Being overweight or obese
  • Having a family history of type 2 diabetes
  • Age 25 or older
  • Multiple gestation (twins, triplets or more)
  • Gestational diabetes in a previous pregnancy
  • Being American Indian or Alaska native, African American, Asian, Hispanic or Pacific Islander

Test Types

Two tests are available to screen for gestational diabetes. Most women will get the oral glucose tolerance test, only following up with getting the three-hour glucose test if their results are out of range.

Oral Glucose Tolerance Test

The oral glucose tolerance test (or glucose challenge test) is routine for all pregnant women. It is far from definitive, so don't worry if you get a call that you need to come back for a follow-up test.

When it's Done: During weeks 24 through 28 of pregnancy, or earlier if you have any risk factors.

How it's Done: There is little you can do to prepare for this test. During the test, you will drink a sugary beverage containing 50 grams of glucose. Your doctor will draw your blood one hour later to see how efficiently your body processes the glucose. Some women may feel nauseated from the sugary beverage.

What Your Results Mean: If your one-hour plasma glucose level is greater than or equal to 140 milligrams per deciliter of blood (mg/dL)—some doctors place the cutoff at 130 mg/dL—gestational diabetes is suspected and further testing is recommended. If your one-hour plasma glucose level is less than 120 mg/dL, you likely do not have gestational diabetes.

Three-Hour Glucose Tolerance Test

This test is to confirm or rule out gestational diabetes.

When it's Done: After you have received an abnormal reading on the one-hour oral glucose tolerance test.

How it's Done: You must fast for 10 to 14 hours before the test. Be sure to discuss any medications you are taking with your doctor to see if they may interfere with the test results. This test is similar to the one-hour oral glucose tolerance test, except the sugary beverage now contains 100 grams of glucose, not 50g. Blood is first drawn before you drink the glucola. This is called your fasting glucose level. Blood is drawn again after one hour, two hours and three hours.

Test-Taking Tips:

  • Due to the required 10- to 14-hour fast, most women schedule the test first thing in the morning.
  • Some people may feel faint or lightheaded during this test. It is a good idea to have a designated driver, if possible, and to bring food to eat when the test is over.
  • Bring a magazine or book so you’ll have something to do between blood tests (if you are having the three-hour glucose tolerance test).

Abnormal readings for each section of the test are:

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


If one of the readings is abnormal, your doctor may suggest some dietary changes and perhaps repeating the test later in your pregnancy. Two or more abnormal readings mean that you probably have gestational diabetes.

Managing gestational diabetes may involve:

  • Changes in your diet, specifically reduction and consistent intake of carbohydrates
  • Regular exercise
  • Insulin
  • Glyburide (an oral medication)
  • Home glucose monitoring throughout the day
  • Additional tests to see how your baby is developing

Fortunately, most women will see their blood sugar levels return to normal within six weeks of delivery. However, having gestational diabetes can indicate an increased risk of developing type 2 diabetes in the future. Maintaining a healthy body weight through a careful diet and regular exercise can help reduce this risk.

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1 Source
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. March of Dimes. Gestational Diabetes.

Additional Reading

By Debra Manzella, RN
Debra Manzella, MS, RN, is a corporate clinical educator at Catholic Health System in New York with extensive experience in diabetes care.