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Can You Eat Before a Gestational Diabetes Test?

By Jessica Bruso ; Updated August 14, 2017

Doctors routinely test pregnant women for gestational diabetes since this condition can harm the baby if it isn't treated. High blood glucose levels may be the only sign of this condition, so this blood test is needed to determine whether a special diet is necessary for the mother to keep the baby safe.


There are two types of gestational diabetes tests. The simpler test is the glucose challenge test, which is the first one that the doctor will order. Should this test indicate a possible problem, you will be asked to return for the longer glucose tolerance test, which will more accurately determine whether you have gestational diabetes.


Both of these tests involve drinking a measured dose of a high glucose beverage and then having your blood drawn and tested. One hour after drinking the liquid for the glucose challenge test you will have your blood drawn. You are not allowed to eat or drink while waiting for the blood draw. With the glucose tolerance test, you have your blood drawn before drinking the beverage and then every hour for the next three hours.


A glucose challenge test result above 130 or 140 mg/dL, depending on the lab, will require you to do the glucose tolerance test at a later date. During this test, your fasting blood glucose level should be below 95 mg/dL, at one hour blood glucose should be below 180 mg/dL, at two hours it should be below 155 mg/dL and at three hours it should be below 140 mg/dL. You will need to make dietary changes and be retested later if your levels are higher than this, and if a repeat of this test also shows abnormal levels you will be diagnosed with gestational diabetes.


The glucose challenge test doesn't require you to fast before having the test, so you should eat normally the day of the test and the day before. With the glucose tolerance test, you need to fast for at least 8 hours before the test, as well as for the three hours you are waiting for your blood draws. Your doctor may ask you to fast for up to 14 hours. During the procedure, blood will be drawn from a vein in your arm or the back of your hand once an hour for three consecutive hours.

Expert Insight

Gestational diabetes testing may be done earlier than 24 weeks if you are at high risk for this condition. Proper treatment for gestational diabetes is needed to lower the risk of complications during the pregnancy, which include the baby growing too big and getting injured during delivery or requiring a C-section delivery.

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