I took DS for his 8 week check today and, although he has put on weight, he's fallen from the 68th centile to the 50th (he's exculsively breast fed).
I thought she was about to tell me I had to use formula and must've looked a bit panicky (first baby) but, instead she just said "if that line wasn't there would you think he was anything other than completely well, happy and healthy? Then don't worry too much about the line. I can see he's fine, just carry on doing what you're doing and come back if you ever need any support".
After all the non-supportive stories I've read on here it was nice to feel backed up!