What does 90% percentile in infant head circumference mean?

Relative study. His rating means that 10% of infants at this age have a larger head circumference (size) while 90% are smaller.If the size has increased from 25-50-75-90% over several months it would suggest growth was too rapid.If usually in that range, it just means the kid has a big head.It hasn't bothered me any, except for having trouble finding a helmet/hat that would fit..