Gestational diabetes  is diabetes brought on by pregnancy. Glucose tolerance test is used to diagnose gestational diabetes. Several tests will be done to check for gestational diabetes in pregnant women. The first one is called a glucose challenge screening. If the results come back positive, then a glucose tolerance test will be performed.
 

What is a glucose challenge screening test ?

This test is a standard test performed during the early part of the third trimester. It is performed between pregnancy week 26 to 28. You don’t need any preparations before this test. No fasting is required for this test. The mother will be given a  glucose solution to drink. Her blood will be drawn  an hour from having the drink. This is because blood glucose level peaks within an hour. This test is done to check how your body processes sugar. Positive results mean blood sugar level  is high. This will  warrant further testing which is done using the glucose tolerance test. Note that not all women who have a positive glucose tolerance test are found to have gestational diabetes.
 

What is the glucose tolerance test ?

Before the test, your doctor will ask you to make sure that you are eating at least 150mg of carbohydrates for three days prior to the time you will be asked to fast  You will also be asked not to eat or drink anything except water  for 14 hours before the test. It is therefore better to have the glucose tolerance test done in the morning. You should also plan to have someone take you home during the test because your energy level may be low and it may result in lightheadedness.

When you get to the doctor’s office , your blood will be dawn to measure your baseline “fasting blood glucose level”. You will then be asked to drink a more concentrated glucose drink than the one used  for the glucose screening test. Your blood will be tested every hour for the next 3 hours.
 

Source : American Pregnancy Association

What do abnormal results mean ?

If  your results come back abnormal your doctor will suggest some dietary changes and test you again later in  pregnancy. If two or more results come back abnormal, you will be diagnosed with gestational diabetes. You health care provider will discuss a treatment plan for you. Treating diabetes during pregnancy is essential for the health of you and your baby.