why isn't there a standardized glucose test ??

Why isn't the rules for glucose screening is not standard all over ?? My first OB told me to fast and I passed that one. Second time I was told to eat and I ate carb heavy breakfast and failed miserably and ended up sitting in 3 hour test. This doctor told me to eat normally (3rd time pregnant). Well I don't eat anything until 9am as I take my thyroid meds and I can only go at 7:30 am or so for the test. Isn't it stupid that this test does not have a general rule everywhere. What if I had one boiled egg before going. I know I will obviously pass and it's still cheating.