A glucose screening test is a routine test during pregnancy that checks a pregnant woman's blood glucose (sugar) level.
Gestational diabetes is high blood sugar (diabetes) that starts or is found during pregnancy.
During the first step, you will have a glucose screening test:
If your blood glucose from the first step is too high, you will need to come back for a 3-hour glucose tolerance test. For this test:
You need to go to the lab one time for a 2-hour glucose tolerance test. For this test:
For either the two-step test or one-step test, eat your normal food in the days before your test. Ask your health care provider if any of the medicines you take can affect your test results.
Most women DO NOT have side effects from the glucose tolerance test. Drinking the glucose solution is similar to drinking a very sweet soda. Some women may feel nauseated, sweaty, or lightheaded after they drink the glucose solution. Serious side effects from this test are very uncommon.
This test checks for gestational diabetes. Most pregnant women have a glucose screening test between 24 and 28 weeks of pregnancy. The test may be done earlier if you have a high glucose level in your urine during your routine prenatal visits, or if you have a high risk for diabetes.
Women who have a low risk for diabetes may not have the screening test. To be low-risk, all of these statements must be true:
Most of the time, a normal result for the glucose screening test is a blood sugar that is equal to or less than 140 mg/dL (7.8 mmol/L) 1 hour after drinking the glucose solution. A normal result means you DO NOT have gestational diabetes.
Note: mg/dL means milligrams per deciliter and mmol/L means millimoles per liter. These are two ways to indicate how much glucose is in the blood.
If your blood glucose is higher than 140 mg/dL (7.8 mmol/L), the next step is the oral glucose tolerance test. This test will show if you have gestational diabetes. Most women (about 2 out of 3) who take this test DO NOT have gestational diabetes.
If your glucose level is lower than the abnormal results described below, you do not have gestational diabetes.
Abnormal blood values for a 3-hour 100-gram oral glucose tolerance test are:
Abnormal blood values for a 2-hour 75-gram oral glucose tolerance test are:
If only one of your blood glucose results in the oral glucose tolerance test is higher than normal, your provider may simply suggest you change some of the foods you eat. Then, your provider may test you again after you have changed your diet.
If more than one of your blood glucose results is higher than normal, you have gestational diabetes.
You may have some of the symptoms listed above under the heading titled "How the Test will Feel."
There is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Taking a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight, but may include:
Reviewed By: John D. Jacobson, MD, Professor of Obstetrics and Gynecology, Loma Linda University School of Medicine, Loma Linda Center for Fertility, Loma Linda, CA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.