You should know in advance that you will be getting the test done. Some doctors, like my clinic, makes you fast so that is definitely something you have to prepare for. So, I would be surprised if you get the test done, if they haven't scheduled it for you tomorrow. I had one around 20w and passed then, because it was so early, I had another at 28w and failed. I had to do the 3 hour testing and failed, so I have GD. But, they may test you around 28 weeks? I've heard that's usually the standard time frame. Good luck and best wishes!
My doctor dint tel me that my test wil b done tmrw..
She just told me to come on 30th.
Thank you