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Growth Charts: Understanding Height and Weight Percentiles

If you are like many parents, the moment when your doctor plots your baby's height and weight on the standardized chart is one of the highlights of your visit. But you might not understand exactly what the results mean. The exact percentile where your child falls is not as important as the general trend over his first few years.

What They Measure

Growth charts compare your child's height and weight to those of other children of the same gender. The number is given as a percentage. For example, a child whose height is in the 50th percentile is the same height as an average child of his age. If your child is in the 90 percentile, he's taller than 90 percent of all children of his age. If he's in the 5th percentile, he's taller than just 5 percent of all children and shorter than 95 percent. Height and weight are products of both genetics and environmental factors. While you can change environmental factors such as diet, you can't change genetics. Your child will probably be similar in height to other members of the family.

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Plotting the Progression

The individual numbers on the chart aren't as important as the trend your doctor sees. A baby who at birth and for the first few months thereafter falls into the 80th percentile for height and the 50th percentile for weight should remain in approximately the same percentile range as she continues to grow. Children's height and weight growth patterns can vary somewhat over time. As long as both numbers change at approximately the same rate, your doctor might not be as concerned as he might be if only one number changed significantly.

Concerning Changes

Weight that falls below the 5th percentile on multiple occasions or that crosses two major percentile lines may indicate failure to thrive, although this is not a perfect science, the April 2011 issue of "American Family Physician" cautions. In a Danish study published in the February 2007 "Archives of Disease in Children," 27 percent of children met the criteria at some point in their first year, although a much lower percentage actually fail to thrive. A drop in the percentile into which your child falls on either height or weight -- or very little growth in both areas over a period of time -- could indicate a medical problem.

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Breast-Fed vs. Bottle-Fed Babies

In the United States, between birth and the age of 2 your baby's length and weight is likely to be measured using charts established by the World Health Organization. BabyCenter explains that the WHO charts "are based on healthy growth patterns for breastfed children." Both the U.S. Centers for Disease Control and Prevention and the American Academy of Pediatrics endorse the WHO charts, BabyCenter notes. The CDC's own growth charts, however, "are based on children who are fed formula only or a combination of formula and breast milk."

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