Can someone explain what the head circumference significance is?
In babies, head circumference (the distance around the largest part of the head) can provide clues about brain development. If a baby’s head is bigger or smaller than most other kids’, or the head circumference stops increasing or increases quickly, it may indicate a problem.
For example, an unusually large head may be a sign of hydrocephalus, a buildup of fluid inside the brain. A head that’s smaller than average may be a sign that the brain is not developing properly or has stopped growing.
Heredity is also a factor. Larger size heads run in my family, but we haven’t seen any connections to mental, physical, behavioral, emotional, or developmental delays… it’s just the way we are. 
Head size can definately run in families. My Grandma has to buy child’s hats because her head is so small!
I’ve heard that head growth can be an early predictor of autism.
I found an article on it here http://www.sciencedaily.com/releases/2008/01/080130140127.htm
Of course, I wouldn’t become too worried because, as everyone has mentioned, kids are just different. But you certainly would want to take some early intervention if you child had the head growth described, I would think.
I really wouldn’t put too much emphasis on the size of a child’s head. The only time to be concerned is if it is not growing enough, or it is very large. If your doctor hasn’t mentioned any concerns, then you should not be concerned. That’s why they measure it every time you go in for a check-up. Like said above, head size is largely inherited. I don’t think it has anything to do with intelligence, certainly not for adults!