I refused the GTT with my last pregnancy. I too was lumped into a high risk catagory with my last 2 pregnancies due to my son being 4.29kgs when born many years previously. I found it ridiculous as my son was to a different father so that had to mean something surely. Mine & DH's first living baby together was 3.45kgs and they chose to overlook that fact and focused instead on my first born's weight. It was crazy. In the end I delivered a 4 kg and a 4.1 kg baby with no problems whatsoever.
It sucks how they want to catagorise people so much now.