February 17, 2005
Gestational Diabetes
Question from Montreal, Quebec, Canada:
Is it normal to do a third 75 gram Glucose Tolerance Test (GTT) after already passing two? I’m currently 30 weeks pregnant with my first baby, have a BMI of 33, but not one family member on either side with diabetes and no other risk factors. Also, I have only gained 13 pounds total, so far, over my pre-pregnancy weight and have been very careful with my diet.
I failed the one hour 50 gram test at 20 weeks with a result of 147 mg/dl [8.2 mmol/L], so at 22 weeks I did a two hour 75 gram GTT with a fasting result of 85 mg/dl [4.7 mmol/L], 150 mg/dl [8.3 mmol/L] at one hour and 78 mg/dl [4.3 mmol/L] at two hours. Then, at 29 weeks, I did the 75 gram GTT again with a fasting result of 82 mg/dl [4.6 mmol/L], 160 mg/dl [8.9 mmol/L] at one hour, and 120 mg/dl [6.7 mmol/L] at two hours. I did not follow any special diet/carbohydrate loading before either 75 gram test.
Now, my doctor said that I have to do another 75 gram GTT at 34 to 36 weeks because she said she is “waiting for when it will happen” which I understand to mean that she believes I will get gestational diabetes and it’s only a matter of time. Is that normal? I understand that my BMI does put me at a higher risk for gestational diabetes, but I’ve now passed two 75 gram tests and am healthy in all other respects including blood pressure. I am planning to refuse the third test, but wanted to know if there was anything in my previous results that would explain my doctor’s insisting on another one at 34 to 36 weeks.
Answer:
I agree that your glucose testing is normal and it is not necessary to keep repeating the test. Your doctor is probably concerned due to your weight and its association with insulin resistance. Instead of repeating the GTT, it may be easier to check a fasting and one hour postmeal blood glucose periodically (such as once a week). This could be done in the doctor’s office using fingerstick blood and a glucometer. The fasting should be 60 to 90 mg/dl [3.3 to 5.0 mmol/L] and the one hour value should be less than 130 mg/dl [7.2 mmol/L]. If you really want to be safe, then, review your diet with a nutritionist to follow the guidelines for gestational diabetes.
OWJ
