Do i have to fast before the glucose tolerance test?

Im supposed to do the initial glucose tolerance test this week and my doctor never told me the guidelines so i was wondering what others were guided to do before. Do i have to fast a certain number of hours? My appt is at 3:25pm so all day sounds terrible! I am going to call my doctors office in the morning to ask for guidelines but i've been having bad luck getting no answer and never getting a call back 😔 if i dont show up to my appt ready to take the test this week I can do it another day but id like to try to get it over with! Thanks all!