Why would I need a prenatal blood glucose test?

Your doctor may want to perform a prenatal blood glucose test to determine if you have diabetes or are at increased risk for gestational diabetes. This test measures the levels of blood sugar (glucose) in your blood. A high blood glucose level can indicate that you have diabetes.

You are at increased risk of gestational diabetes if you:

• Are over age 25.
• Are obese.
• Have a family history of diabetes.
• Have previously had gestational diabetes, a very large (over 9-1/2 pounds) baby or stillborn.
• Are of African-American, Hispanic/Latino American, Pacific Islander or American Indian descent.

Some doctors believe all women should be screened for gestational diabetes, because half of women with gestational diabetes do not have any of these risk factors. Discuss with your doctor whether a screening test is right for you.

When is a blood glucose test done?

A blood glucose test is usually done between the 24th and 28th weeks of pregnancy. Women who are considered at high risk (including women who have had gestational diabetes in a previous pregnancy) often are screened at an early prenatal visit and, if test results are normal, screened again at 24 to 28 weeks. According to the American Diabetes Association, women younger than 25 with no risk factors for diabetes, do not require screening because they have a very low risk of developing gestational diabetes.

How is the glucose challenge test done?

The first test is called a glucose challenge test. You will be asked to drink a sugar solution. After you have waited an hour, blood is drawn from a vein in your arm, and the glucose level is checked. About 15 percent of pregnant women given a glucose screening test have abnormal levels of blood glucose. If you have an abnormal level, then a second test, called an oral glucose tolerance test or a fasting glucose tolerance test, is performed.

What is involved in an oral glucose tolerance test?

An oral glucose tolerance test is another type of test to screen for diabetes. It is the most accurate way to determine if you have gestational diabetes. For this follow-up test, you need to fast overnight. You are then given another sugar solution to drink. Blood samples are collected periodically over a three-hour period to measure your blood glucose at different times.

What does an abnormal result mean?

A woman has gestational diabetes when she has any two of the following:

• A fasting blood glucose of more than 95 milligrams of glucose per deciliter (mg/dL) of blood
• A 1-hour glucose level of more than 180 mg/dL
• A 2-hour glucose level of more than 155 mg/dL or
• A 3-hour glucose level of more than 140 mg/dL

Will gestational diabetes harm my baby?

Women with gestational diabetes usually do not have an increased risk of having a baby with a birth defect. Poorly controlled gestational diabetes slightly increases the risk of stillbirth. However, stillbirth is rare. There is also a risk that the baby will be very large.

How is gestational diabetes managed?

Once gestational diabetes is diagnosed, you may be able to control your blood sugar levels with diet and exercise. If your doctor determines that you have gestational diabetes, you will need to monitor your glucose levels at home. In some women, insulin injections are required.

In most cases, diabetes disappears soon after giving birth. Women who have had gestational diabetes do, however, run a greater risk of developing type 2 diabetes later in life. For this reason, it is important to continue to have your blood sugar levels monitored after delivery.