How is gestational diabetes diagnosed?

Your health care team will check your blood glucose level. Depending on your risk and your test results, you may have one or more of the following tests.

Fasting Blood Glucose or Random Blood Glucose Test

Your doctor may check your blood glucose level using a test called a fasting blood glucose test. Before this test, your doctor will ask you to fast, which means having nothing to eat or drink except water for at least 8 hours. Or your doctor may check your blood glucose at any time during the day. This is called a random blood glucose test.

These tests can find some people with gestational diabetes, but other tests are needed to be sure diabetes is not missed.

Your health care provider will check your blood glucose level to see if you have gestational diabetes.

Screening Glucose Challenge Test

For this test, you will drink a sugary beverage and then have your blood glucose level checked an hour later. This test can be done at any time of the day. If the results are above normal, you may need further tests.

Oral Glucose Tolerance Test

If you have this test, your health care provider will give you special instructions to follow. For at least 3 days before the test, you should eat normally. Then you will fast for at least 8 hours before the test.

The health care team will check your blood glucose level before the test. Then you will drink a sugary beverage. The staff will check your blood glucose levels 1 hour, 2 hours, and 3 hours later. If your levels are above normal at least twice during the test, you have gestational diabetes.

Above-Normal Results for the Oral Glucose Tolerance Test*
Fasting	95 or higher
At 1 hour	180 or higher
At 2 hours	155 or higher
At 3 hours	140 or higher
Note: Some labs use other numbers for this test. *These numbers are for a test using a drink with 100 grams of glucose.

source: http://diabetes.niddk.nih.gov/dm/pubs/gestational/index.htm