To further add to Christina's post on this, I just finished giving a presentation that discussed the current growth charts. Here's a snip from what I presented.: The NCHS growth charts are based on information collected by the Fels Research Institute from 867 infants born between 1929 and 1975. In that study, the feeding method was known for 75% of the infants - only 17% were exclusively breastfed, and few were breastfed for more than 3 months. Furthermore, the breastmilk substitutes used at that time were less similar to human milk - higher protein & fat, and the infants were more likely to be given solid foods before 4 months. Additionally, measurements were taken at 3- rather than 1-month intervals, which obscured some of the short-term variations in infant growth. It is projected that more than 5% of all infants, regardless of feeding method, will fall below the 5th percentile in any given month. Because of this, there are a number of investigators who suggest that the NCHS charts are inappropriate for use with breastfed infants. Katherine Dewey, who has worked extensively with studying growth parameters of breastfed infants has found that breastfed infants who fell below the 5th percentile were much larger than would be expected, averaging 31% for the six 1-month intervals up to age 6 months and 52% for the six 1-month intervals between 6 and 12 months. Although these percentages sound alarming, these were healthy infants, fed on demand, and who received solids at 4-6 months. As far as activity level, sleeping pattern, or morbidity, these infants were no different from the breastfed infants with faster growth rates.