Yep had mine at 28 weeks. If youre only doing the short glucose tolerance test then you dont need to prepare for it, on the day they give you the glucose drink, and you have to sit quietly for an hour and then they do a finger pr*ck test. Only thing i can suggest is dont eat anything too sugary the day prior to your appointment as it may effect your sugar levels and youll have to do the long glucose test which takes a few hours.