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How is gestational diabetes diagnosed?

Screening for gestational diabetes is generally done between the 24th and 28th weeks of pregnancy and requires an oral glucose tolerance test. (Be sure to ask your healthcare professional about this test). This test involves drinking a liquid that contains glucose, which causes blood glucose levels to rise within 30 to 60 minutes. A blood sample is taken from a vein in your arm about 30 minutes after drinking the solution.

The blood test measures how the glucose solution was processed by the body. If your test results are not normal, you will have a similar test that requires you to fast beforehand. If this second test shows abnormal results, you have gestational diabetes.
Women with gestational diabetes often have no symptoms. For this reason, experts recommend a glucose screening test between the 24th and 28th week of pregnancy. If you've had gestational diabetes in a previous pregnancy, you may also have screening earlier in this pregnancy.

If the results from this one-hour glucose screening test are abnormally high, you may be asked to do a 3-hour glucose tolerance test. If 2 out of 4 values on the tolerance test are high, your doctor will diagnose gestational diabetes.

It is recommended that all pregnant women be screened for gestational diabetes mellitus between 24-28 weeks gestation. Women with risk factors should be screened earlier. Screening consists of a 50 gram oral glucose load followed by a venous plasma glucose measured 1-hour later. If the plasma glucose level is 140 mg/dl or greater a 3-hour glucose tolerance test (GTT) is required. After fasting, a blood glucose is drawn and the woman is given a 100-gm glucose load, followed by venous plasma glucose levels measured 1, 2, and 3 hours later. If two or more of the blood glucose values are greater than the reference values the test is considered diagnostic of gestational diabetes mellitus.

Gestational diabetes produces no symptoms -- most women feel fine. Women with a higher chance of developing gestational diabetes are checked between 24 and 28 weeks of their pregnancy with a screening glucose challenge test. It is a check of your glucose level one hour after you drink a special sweet beverage. A result of 140 mg/dl or more means that more testing may be needed. Some doctors recommend more testing if your level is 130 mg/dl or more.

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 eight 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 identify gestational diabetes in some women, but other tests are needed to be sure diabetes is not missed. Screening glucose challenge test: For this test, you will drink a sugary beverage and 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. You will be asked to eat normally for at least three days before the test. Then, you will fast for at least eight 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 one hour, two hours, and three hours later. If your levels are above normal at least twice during the test, you have gestational diabetes.

This answer is based on source information from the National Institute of Diabetes and Digestive and Kidney Diseases.

During your first trimester, your doctor will determine your risk factors for gestational diabetes. If you are at risk of developing diabetes during pregnancy, your doctor will monitor your blood sugar at a later stage of your pregnancy, depending on how high your risk factors are. If you are at risk, you will take a blood glucose test to determine whether your blood sugar is too high.

Talk to your doctor early on in your pregnancy about the risks of developing gestational diabetes.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.