August 24, 2003
Gestational Diabetes
Question from Sacramento, California, USA:
I am 37 years old and in my third pregnancy. During my previous two pregnancies, I passed my glucose tests, and this time I did the one-hour test at about 15-16 weeks because of my age. I failed the screen with a value of 170 mg/dl [9.4 mmol/L]. I subsequently took the three-hour test and passed.
My doctor want to test again when I am 24 weeks along and has recommended that I go directly to the three-hour test since the vast majority of pregnant women who have failed the one-hour will fail it again. Is this true? I’ve read some places that you should avoid fruit, fruit juices and cold cereal before the one-hour test, but was only told to avoid eating a heavy meal right before. Why is fasting required for the three-hour test but not for the one-hour test? If many websites recommend the fasting glucose test, why do pregnant women always seem to get the three-hour test? (It would be much more convenient for those of us with little children to do the fasting test).
Answer:
If you failed the one-hour test already, it is not worth it to repeat it. The three-hour test is more sensitive in detecting diabetes whereas the one-hour test is only a screen.
The one-hour test was designed for convenience allowing it to be done in the office at any time of day. The down side is that when you are not fasting, you are more likely to have an abnormal result, particularly if you had some sugar intake ahead of time such as fruit juice. If you take the test fasting, then it will work better as a screen. The fasting is required for the three-hour test because part of the test is to determine what the fasting blood sugar value is.
Most women pass the screening test and do not require the more lengthy three-hour test. However, doctors will vary in their recommendations for testing. Once again there is a trade off in large scale screening, convenience and cost.
OWJ
