Percentiles, Explained

Percentiles, ExplainedIf you’ve taken your little one to a well-child checkup, you’ve probably heard the numbers. In fact, you might be more motivated to know the numbers than your pediatrician. In the many ways we concern ourselves with our children’s development and milestones, growth percentiles are among the most tangible. “We’re in the 90th percentile,” your friend touts. You might feel anything from disappointment in your child’s growth to annoyance at your friend’s pride. Take a deep breath and let those feelings go, because that is not what the growth chart is about.

Percentiles provide comparison of typical growth, not for the sake of comparison so much as to ensure your child’s general well-being. If your child is in the 50th percentile for height, among 100 children about fifty would be taller and fifty shorter than your child. Height and weight measurements continue through the years of adolescence, while doctors only monitor head circumference for the first three years of life when development is so rapid. Observing head circumference allows doctors to assess adequate brain development in a child and rule out any concerns if little or excess growth occurs.

Two common charts come from the Center for Disease Control and Prevention (CDC) in the United States and the World Health Organization (WHO). WHO growth standards utilize 6 countries in the world that provide “optimal growth” environments for children ages 0 to 59 months. The six countries include: Brazil, Ghana, India, Norway, Oman, and the United States. This means that, among other things, both mothers and babies studied met the minimum international nutrition recommendations for optimal health. The project was funded by a combination of governments, United Nations agencies, and the Bill and Melinda Gates Foundation.

WHO more fully represents growth standards associated with breast-fed children compared to the CDC. Even the CDC says its own charts lack some of the methodological standard that WHO utilizes. CDC uses small sample sizes in the first 6 months of life compared to WHO’s frequent evaluations over time (longitudinally) of a more representative population. The CDC’s charts were updated in 2000 to better represent America’s diversity.

The bottom line is WHO growth standards more fully incorporate breast-fed children in their growth curves and have more accurate data in the early months. WHO also more fully represents a global perspective on “optimal” growth as opposed to simply a comparison of typical growth in the United States. This could matter for a family who has a healthy but lower birth weight child or a child who is exclusively breast fed beyond the more typical 0-6 months in the United States.

Ultimately, you know your child best. Your child’s individual curve is most important. If your child has always stayed in the 25th percentile, your child’s smaller stature is not necessarily concerning. If your child was always in the 75th percentile and, in the last year, has fallen to the 25th percentile, your doctor might be concerned about why your child has not continued to grow as is typically (or optimally) expected. Even still, a small dip or jump here and there can be typical as children hit growth spurts, have illnesses, and picky habits at different times. Genes, the environment, nutrition, and activity can affect your child’s growth.

Growth charts offer a clinical impression of a child’s growth at any given age, but if used wisely, they also provide room for the nuances of every individual child’s unique story.

Lynette Moran shares her life with her husband and two sons, ages 1 and 3 years. She has cloth diapered both since birth and enjoys all things eco-friendly and mindful living.

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