What do you think of this paper:
International standards for newborn weight, length, and head circumference by gestational age and sex: the Newborn Cross-Sectional Study of the INTERGROWTH-21st Project
http://www.thelancet.com/journals/lancet/article/PIIS0140-6736%2814%2960932-6/abstract
http://www.newscientist.com/article/dn26167-all-newborns-should-be-similar-size-in-ideal-conditions.html