Set your appointment for first thing in the morning and start your fast the previous night. That'll help! But I agree I don't understand why they're having you fast in the first place!
I'm not sure why they would be having you fast. They draw most blood for labs regardless if they are testing for baby. I agree with tamararae19, I would call them to double check.
It never hurts to double check with them about it. That seems a little weird. Any idea why they want you to fast?