Don't worry, I was told at 32 week scan that my baby boy is 1600grams and still in the 50 percentile. I have been told he will be small because his cord didn't form right and only has one artery. I have been reassured that this is fine and I'm not worried, at the end of the day I'm the one that has to push him out. Funny though his measurements read at about 2 weeks behind except for his head, it is on track, come on if I'm going to have a small baby you would think the painful part would be more cooperative.