Quoting Will☮Creedence:" <blockquote><b>Quoting lolajessup:</b>" <blockquote><b>Quoting Will☮Creedence:</b>" ... [snip!] ... heart is HUGE. It's supposed to be 1/3 the size of the chest. It's 121mm and the chest is like 192mm. So it's more than 1/2."
I went through something similar with my middle baby as far as the legs go. It was both his legs and arms that were short though. I'm surprised they could get a good weight estimate with the leg issue. That was always the problem for us. My son's long bones (upper arms, upper legs) were significantly shorter proportionally than the rest of his body so his weight estimate was always off by about 2lbs. I was actually induced early because they thought he was IUGR. (No i don't have boring pregnancies... lol) He ended up being 6lbs 7oz, but they estimated he was going to weigh under 5lbs.
After he was born, along with the long bone issue, both of his hands have a single simian crease (there's a different, more correct name for it now, but the monkey name stuck../shrug). I had to deliver with a NICU team there just in case and he had to be evaluated by the geneticist on call. That started a whole process of seeing the geneticist every month or so until he was about 6 months old.
The end result is that his genes are quirky, but no major issues. I'm summarizing. He has some extra info on his Y chromosome. His height/weight is about 50th percentile as of his 2 year check up. His brothers are both very very tall for their age, so he is going to be shorter but I can live with that.
Good luck and I hope they figure out what's going on. Nothing's worse than not knowing.