What to Expect from a Glucose Tolerance Test

Sometimes called a gestational diabetes test, glucose screening is crucial to detecting the often-symptomless pregnancy complication.

This simple test looks for potential cases of gestational diabetes, to help prevent complications in your pregnancy.

When is the test taken?

Glucose screening is usually done between 24 and 28 weeks of pregnancy. If the test, which screens for gestational diabetes, reveals elevated levels of blood glucose (sugar), a glucose tolerance test is then given to confirm the gestational diabetes diagnosis.

Who needs to take the test, and why?

Although traditional guidelines call for glucose screening during pregnancy if you have certain risk factors—you are over 30, have a family history of diabetes, had a troubled earlier pregnancy, or are obese—the U.S. Preventive Services Task Force recommends all pregnant women be screened for gestational diabetes. The independent task force's 2015 research, published in the Annals of Internal Medicine, found that screening and treatment reduced the risk of preeclampsia and birthing an overly large baby. 

So even if you don't meet any of the risk criteria, your practitioner may still advise taking this safe and simple test, because about half of the women who develop gestational diabetes have no known risk factors. About 15 to 20 percent of women who take this screening will show abnormal levels of glucose and will be given the more involved (and more precise) glucose tolerance test. About 15 percent of the women given the second test will be diagnosed with gestational diabetes.

Gestational diabetes can be controlled by diet, exercise, or insulin. But if the elevated glucose levels remain undetected, the excess sugar in the mother's blood raises the odds of the baby being overly large, or macrosomic—generally 9 pounds, 14 ounces or more. Macrosomic babies may have difficulty fitting through the birth canal and are at risk for health problems such as jaundice, low blood calcium levels, or hypoglycemia. Luckily, glucose screening and glucose tolerance testing can help you detect gestational diabetes early, and give you a chance to minimize the risks of this condition.

What's involved?

For glucose screening, you will be given a syrupy (and a little unpleasant) glucose solution to drink. An hour after you've finished drinking the beverage, a blood sample is taken from a vein in your arm, and the glucose level is analyzed. If it's found to be high (generally over 130 mg/dL), then you'll be asked to take the glucose tolerance test. This involves fasting overnight, then drinking a solution with an even higher dose of glucose. Your blood will then be sampled several times over a period of about three hours and tested for abnormal levels of glucose.

When are test results available, and how are they interpreted?

Test results are available immediately. If the test reveals that you have gestational diabetes, you are not alone. It is one of the most common complications of pregnancy—about three to five percent of all pregnant women in the United States have the condition. Generally, if you develop gestational diabetes, you may need to make lifestyle changes and to be closely monitored for the duration of your pregnancy. But take comfort in the fact that gestational diabetes almost always disappears immediately after birth.

Parents Magazine


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