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Question:

From Michigan, USA:

At 27 weeks into my pregnancy, I had a 1-hour glucose tolerance screening test. My glucose level was 150. Needless to say, I was scheduled for a 3-hour GTT glucose tolerance test. I was only told to fast for 12 hours before, drinking nothing but water. I was not told to follow any particular "diet" 3 days prior to the test or even 24 hours prior to the test.

During the test, I noticed that my blood was not being drawn exactly on the hour. My blood was being drawn every 45 to 50 minutes. My results came back with only one high reading: 85 (Fasting), 153 (1 hour), 167 (2 hour), and 131 (3 hour).

I was sent to a maternal-fetal specialist who said that I do not have gestational diabetes. He ordered an ultrasound which showed that the baby is perfectly average-sized. I have also had two visits with my obstetricians since then where the height of my fundus is exactly the week that I am at. If I had gestational diabetes, wouldn't the height of my fundus start to become larger than normal?

The maternal fetal specialist wanted me to repeat the test to basically confirm that I do not have gestational diabetes. My OBs are wanting to treat me as though I am borderline unless the second test proves otherwise.

So, my questions are, what are the glucose tolerance testing procedures recommended for the patient and the test administrator? What should my diet consist of 3 days prior to the test? What should my diet consist of 24 hours prior to the test? What affect will blood being drawn every 45 to 50 minutes have on the test results?

Thank you for your help with any of these questions -- it has been very difficult to find information about the administration of these tests.

Answer:

The following is the guideline for performing a 3 hour glucose tolerance test:

  1. 1-hour 50 gram glucose challenge result greater than or equal to 140 mg/dl
  2. Overnight fast of 8-14 hours
  3. Unrestricted diet and activity for 3 days including greater than or equal to 150 grams carbohydrate
  4. Seated, not smoking during test.

The diagnosis of gestational diabetes is made if two or more values are met or exceeded on the 3-hour test:

Fasting 105 mg/dl
1 hour 190 mg/dl
2 hour 165 mg/dl
3 hour 145 mg/dl

(Maternal-Fetal Medicine: Principles and Practice, Creasy and Resnik, ed., 3rd edition, page 969.)

You were appropriately scheduled for a 3-hour test. However, the testing procedure was adhered to rather loosely. But, if the blood was drawn early, if anything I would expect the glucose value to be higher than expected. You had a single slightly elevated value which does not make the diagnosis of gestational diabetes.

Rescreening is reasonable, since as many as 30% of women who have an initially normal 3-hour test may subsequently test positive. The fact that your baby is growing normally would suggest that you do not have gestational diabetes.

OWJ

Original posting 15 Mar 1998
Posted to Gestational Diabetes

  
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Last Updated: Tuesday April 06, 2010 15:08:56
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