During pregnancy your doctor will recommend certain basic investigation such as routine urine examinations, ultrasound, blood examination for haemoglobin, blood grouping and typing and blood sugar testing. Tests to diagnose gestational diabetes are usually done between 24 and 28 weeks of pregnancy but they may be done earlier if you are at high risk of developing gestational diabetes (the test may be done before the 13th week of pregnancy). Read to know about the tests (fasting blood glucose or random blood glucose test, 1 hour glucose tolerance test and 3 hour glucose tolerance test) done to diagnose gestational diabetes.
Fasting blood glucose or random blood glucose test: For the fasting blood glucose test, your doctor will advise you to fast for at least 8 hours (which means that you have nothing to eat or drink except water for at least 8 hours). In random blood glucose test your blood glucose is tested at any time during the day. Both these tests can detect gestational diabetes in some women, but your doctor may recommend other tests to be sure that diabetes is not missed.
1 hour glucose tolerance test: The 1 hour glucose tolerance test is done on pregnant women to screen for gestational diabetes. Unlike the 3 hour glucose tolerance test you will not be advised to fast prior to this test. For this test you will be given 50 gm of glucose solution to drink. The solution has to be consumed within 5 minutes. Some women may feel nausea after drinking the solution as it is very sweet. The blood sample for glucose testing is taken after 1 hour. Based on the results of 1 hour glucose tolerance test the following diagnoses may be made:
- Normal screen: if the blood sugar level is <140 mg/dL (7.8 mmol/L)
- Abnormal result: If the blood sugar level is >140 mg/dL (7.8 mmol/L) (OGTT is recommended)
3 hour glucose tolerance test: The 3 hour glucose tolerance test is considered as the gold standard for making the diagnosis of type 2 diabetes but it is presently most often done to diagnose gestational diabetes. If the result of 1 hour glucose tolerance test is abnormal, the 3 hour glucose tolerance test is recommended to confirm the diagnosis of gestational diabetes.
You will be advised to fast overnight (at least 8 but not more than 16 hours) before the 3 hour glucose tolerance test. The next morning, a sample for fasting plasma glucose level is taken. After this you will be given 75 grams of glucose (100 grams for pregnant women) solution to drink. Then blood samples are taken to measure the blood glucose. In the classic test blood glucose level is measured five times over a period of 3 hours.
Gestational diabetes is diagnosed based on 3 hour glucose tolerance test if any two of the following after 100g OGTT is positive:
- Fasting plasma glucose > 95 mg/dl.
- 1-hour glucose > 180 mg/dl.
- 2-hour glucose level > 155 mg/dl.
- 3-hour glucose level > 140 mg/dl.
Glucose tolerance test can help in early diagnosis of gestational diabetes. Early diagnosis and appropriate management can help to prevent the gestational diabetes related complications both in the mother and baby.
Read more articles on Gestational Diabetes
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