Gestational Diabetes Test: What, Why and How

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About Gestational Diabetes

When a woman becomes pregnant, her body undergoes many changes. One of those changes occurs when the pancreas begins to make a hormone that can negatively affect the function of insulin, thereby causing gestational diabetes. Because of this risk, pregnant women are given a gestational diabetes test as a regular part of their pre-natal care.

Testing for gestational diabetes may occur between the 24th and 28th week of pregnancy in most women. Those at higher risk for developing gestational diabetes may need to take the test earlier in their pregnancy. According to WebMD, this testing may occur prior to the 13th week for those women who are at higher risk or who have had gestational diabetes previously.

Oral Glucose Tolerance Test

The oral glucose tolerance test is commonly given to pregnant women to screen for gestational diabetes. This test involves the patient consuming a sweet liquid (glucose). An hour after the glucose in consumed, blood is drawn and tested. If the results are too high, additional testing will be done which will take approximately three additional hours.No preparation is needed for this test and it can be done at any time of day.

WebMD explains the testing and results process by stating, “A blood glucose of 140mg/dL will identify 80% of women with gestational diabetes. When that cutoff is lowered to 130mg/dL the yield increases to 90%. If your blood glucose level was greater than 130 mg/dL, your provider will likely recommend you take another diabetes screening test that requires you to fast (not eat anything) before the test.”

100-Gram Oral Glucose Tolerance Test

This test follows the oral glucose tolerance test when its results were considered to be too high. In this test, blood is tested four times during the three hours after a drinking a beverage compared to cola.

Preparation is needed for this test, beginning with an overnight fast. When arriving at your testing appointment, an initial blood draw is taken so there is a fasting blood sugar level measurement to compare the upcoming draws with.

Another sweet liquid is then given to the patient to drink, with a glucose concentration higher than in the one used in the initial screening. Approximately every hour after that for thenext three hours, blood is drawn and tested. According to WebMD, you are diagnosed as having gestational diabetes when two of the tests have results that are abnormal (higher than average).

The preliminary gestational diabetes test is a routine part of pre-natal care and is nothing to cause concern. After giving birth, the gestational diabetes can clear up. A blood sugar test may be given after the baby is born to ensure blood sugar levels are normal.


Gestational Diabetes. Mayo Clinic Staff. March 28, 2009.

WebMD. Pregnancy and Gestational Diabetes. Reviewed by John A. Seilbel, MD. March 08, 2009.

Health & Pregnancy: Gestational Diabetes – Topic Overview. Last updated November 4, 2009.

Health & Pregnancy: Pregnancy and Gestational Diabetes. Reviewed by Mikio A. Nihira, MD. December 20, 2009.