I think they are just being cautious that nothing is missed. After all you can't possibly just have a big baby for any other cause. my eldest was bigger than your bubs and I passed the first test no one ever mentioned going for another afterwards. They tested bubs blood sugar after birth which was also aced and that was the end of it. We just make big babies apparently. If you don't want to do it perhaps call and talk to your doctor to see if it is really necessary.