3 hour glucose tolerance test for gestational diabetes?

I flunked my first glucose test and have to take the 3 hour one. I was hypoglycemic before pregnancy, and I know that has to affect the results, because I can't eat anything for 12 hours before the test, then drinking the sugary drink will cause my blood sugar to skyrocket. Does that mean I have gestational diabetes? I know hypoglycemia is low blood sugar and diabetes is high. How do they tell the difference in the test? I've tried researching it and can't find anything online.