P is for Pattern
When your doctor plots those dots on your baby's growth chart, she gets an instant snapshot of how your infant compares to other American babies of the same age. Separate charts are used for each gender, so your daughter will be compared to other baby girls and your son to other baby boys.
The "percentile" simply reveals where your baby growth ranks in comparison to the national survey. For example, if your daughter is in the 25th percentile for weight, that means she weighs more than 25 percent of baby girls her age, and less than 75 percent of baby girls her age.
There's no need to nibble your nails with worry about the percentile numbers you hear at any one office visit. "The important thing is the pattern over time," says Bradley S. Miller, MD, PhD, assistant professor of pediatric endocrinology at the University of Minnesota. "Looking at one point in time is not as helpful as looking at the comparison from one time to another."
According to the American Academy of Pediatrics, in a healthy, well-nourished baby, the height, weight, and head-size measurements will increase at a predictable rate, creating a curve along the growth chart. Each child is unique, so your pediatrician expects your baby to follow her own unique curve. How she compares to other babies isn't nearly as important as, "Is she still following her own established pattern?"