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From the U.S. Navy:

I am pregnant and almost 39. I failed the 1-hour glucose challenge (nonfasting) test by 3 mg/dl (scored 143), and so took the fasting 3-hour test. How many hours should I have fasted for the test, and what is the impact of drinking water during the fast and/or during the time after drinking the glucose solution? My doctor and the lab techs disagree on this.


"Fasting" is usually described as being overnight (after supper the evening before would be fine; after a bedtime snack would be okay)... it takes about 4-6 hours for the sugar to stabilize at a "fasting level."

I have no reluctance to have the patient drink PLAIN water (but not coffee, or other beverages with anything in them) before testing the "fasting blood sugar." I guess that theoretically, water might dilute the sugar level a bit, and hence lower it a bit, but I'm not really sure in a situation where the sugar is near normal (although this is useful in diabetics with high sugar, to help lower their sugar levels).

If your fasting value is truly fasting, except for water, I'd have to say your body cannot maintain a normal blood sugar in the face of the stress of pregnancy, and I'd strongly suggest starting a gestational diabetes regimen to help protect the pregnancy.


Original posting 22 Jul 96


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Last Updated: Tuesday April 06, 2010 15:08:52
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