Tuesday, July 17, 2012

Pediatric Growth Charts

When I had my first child, I often wondered if he was gaining enough weight.  I breastfed him exclusively and found it difficult to assess if I was producing enough milk for his needs.  Looking at his growth in comparison to standardized growth charts was the only way for me to determine if he was getting enough breastmilk.  My baby was always on the smaller side and that concerned me.  However, as I began researching the topic, I began to realize that the growth charts in use today is very different from the growth charts used several years ago.

Prior to the year 2000, most providers referenced a growth chart from 1977.  The chart developed in 1977 was from a single study whose data was collected from primarily "formula fed, white middle-class infants in a limited geographic area of southwestern Ohio from 1929–75."  This chart was even adopted internationally by the World Health Organization.

The problem with this chart was it tried to compare children from around the world to a select group of people in the United States.  As you know, many people around the world differ in size according to their nutritional status and ethnicity among other factors.  It was this discrepancy that led to the  development of the new guidelines in use today.

In the US, the current growth charts now include a Body Mass Index (BMI) for age charts.  "BMI (wt/ht2) is calculated from weight and height measurements and is used to judge whether an individual's weight is appropriate for their height. BMI is the most commonly used approach to determine if adults are overweight or obese and is also the recommended measure to determine if children are overweight. The new BMI growth charts can be used clinically beginning at 2 years of age, when an accurate stature can be obtained."  The new charts also had a revised head circumference chart which "also show some noticeable differences when compared to the earlier charts. Compared to the original infant charts that were based on primarily formula-fed infants, the revised growth charts for infants contain a better mix of both breast- and formula-fed infants in the U. S. population."

The Centers for Disease Control (CDC) recommends the charts developed by the World Health Organization (WHO) for children 0-2 years old and the CDC growth charts to monitor children 2 and older in the United States.  There are separate charts because the WHO chart only covers children until they are 5 years old.

The WHO standards "establish growth of the breastfed infant as the norm for growth.  The WHO charts reflect growth patterns among children who were predominantly breastfed for at least 4 months and still breastfeeding at 12 months."  "The WHO standards provide a better description of physiological growth in infancy.  Clinicians often use the CDC growth charts as standards on how young children should grow. However the CDC growth charts are references; they identify how typical children in the US did grow during a specific time period. Typical growth patterns may not be ideal growth patterns. The WHO growth charts are standards; they identify how children should grow when provided optimal conditions."  For example, according to the CDC growth chart reference, if a "typical" growth pattern for a particular region is for children to be overweight, it is not an "ideal" growth pattern and children should not be compared to that reference.

"The CDC growth charts are based on primarily formula fed infants.  Only about 50% of infants measured to construct the growth reference charts were ever breastfed.  By 3 months of age, only 33% were breastfed.  In the US, 75% of infants born in 2008 were ever breastfed, 44% were breastfed for at least 6 months and 24% were breastfed at 12 months.  Consequently, the CDC growth charts may not adequately reflect the current growth patterns of infants in the US and they do not reflect a growth pattern typically seen in breastfed infants."

"Growth patterns differ between breastfed and formula-fed infants. Beginning around 3 months of age weight gain is generally lower for breastfed infants than for that of the formula-fed infant.  Linear growth generally follows a similar pattern for both breast- and formula-fed infants.  Formula-fed infants tend to gain weight more rapidly after age 3 months, they may be more likely to cross upward in percentiles on the WHO growth charts, perhaps becoming classified as overweight."

The WHO Standards were developed from data collected from "The WHO Multicentre Growth Reference Study (MGRS)."  "The WHO Multicentre Growth Reference Study (MGRS) was undertaken between 1997 and 2003 to generate new growth curves for assessing the growth and development of infants and young children around the world.  The MGRS collected primary growth data and related information from approximately 8500 children from widely different ethnic backgrounds and cultural settings (Brazil, Ghana, India, Norway, Oman and the USA)."  "The children included in the study were raised in environments that minimized constraints to growth such as poor diets and infection. In addition, their mothers followed health practices such as breastfeeding their children and not smoking during and after pregnancy."

"The MGRS was designed to provide data that describe “how children should grow,” by including in the study’s selection criteria specific health behaviors that are consistent with current health promotion recommendations (e.g., breastfeeding norms, standard pediatric care, non-smoking requirements). This new approach is fundamentally different from that taken by the traditional descriptive references. By adopting a prescriptive approach, the protocol’s design went beyond an update of how children in presumably healthy populations grow at a specific time and place and explicitly recognizes the need for standards (i.e., devices that enable value judgments by incorporating norms or targets in their construction). Arguably, the current obesity epidemic in many developed countries would have been detectable earlier if a prescriptive international standard had been available 20 years ago."  This study "reiterate the fact that child populations grow similarly across the world’s major regions when their needs for health and care are met."

A result of the new standards will be "that stunting (low height for age) will be greater throughout childhood when assessed using the new WHO standards compared to the previous international reference. There will be a substantial increase in underweight rates during the first half of infancy (i.e., 0-6 months) and a decrease thereafter. For wasting (low weight for length/height), the main difference between the new standards and the old reference is during infancy (i.e., up to about 70 cm length) when wasting rates will be substantially higher using the new WHO standards. With respect to overweight, use of the new WHO standards will result in a greater prevalence that will vary by age, sex and nutritional status of the index population."  This is not surprising considering the previous reference was based on "formula fed, white middle-class infants in a limited geographic area of southwestern Ohio."

The new standards establish the following cutoffs:
"Infants and children with a weight-for-length < 2nd percentile are classified as low weight-for-length.
Infants and children with a length-for-age < 2nd percentile are classified as having short stature.
Infants and children with a weight-for-length > 98th percentile are classified as high weight-for-length."

When a child transitions after the age of 2 "from the WHO weight-for-length chart to the CDC BMI-for-age chart may result in a change in a child's percentile classification" because of:
Apparently, many parents do not understand growth charts.  If a doctor is using the CDC growth chart instead of the WHO growth chart, who can blame them?  There was a study published in the journal Pediatrics in October 2009 titled, "Do Parents Understand Growth Charts?  A National Internet Based Survey."  "Understanding a growth chart requires the ability to understand several concepts, including trending over time, proportionality (height compared with weight), and graphical presentation. Health care providers may mistakenly assume that parents understand these concepts."  The study found "the majority of this survey's respondents were not able to comprehend growth chart data fully. The concept of percentile seemed particularly difficult for respondents to understand. Although most reported having heard of the term, many could not identify the percentile of a point shown on a growth chart, and an even larger number could not identify the definition of the term percentile."  "A significant number of respondents were mistakenly concerned about a proportionate child who is smaller (shorter and lighter) than average but growing normally, and they thought that it would be healthier for the child to be at higher percentiles. This confirms the findings of a recent study in which mothers misinterpreted percentile as indicating the percentage of children at that height or weight and thought that growth curves were more satisfactory at higher percentiles. Most respondents expressed concern if a child's growth was shown to measure in the 10th percentile for both height and weight, whereas significantly fewer showed concern about the health of a child who was in the 90th percentile for height and weight. Also, respondents showed much greater concern about a child's absolute weight, compared with a child's height or height/weight proportionality."  The study concluded, "few parents understand growth charts and the implications of the data they present."  The authors recommend, "non–growth chart-based approaches to teaching parents about their children's growth should be considered, because our results reveal that many parents clearly lack knowledge about the growth process and are uncertain about the best ways to assess a child's growth or, indeed, whether tracking a child's growth is even important. For example, our results indicate that parents typically rely on comparisons they make with other children of similar age, rather than growth charts, to judge their child's physical development, which can be deceiving when a large proportion of children in a community are overweight."

The big take home message for me, from all of this, is that if my child is proportionally growing normally (height and weight) and within the 2-98% cutoff, then it is OK.  My child may not necessarily need to be in the higher percentiles to be considered "healthy."  Also, I need to make sure my provider is using the WHO standards when evaluating my breastfed infant as opposed to the CDC references which show typical growth patterns that might not be ideal growth patterns.

Here are the links to the WHO Growth Charts:
Birth to 24 months: Boys Weight-for-length percentiles and Head circumference-for-age percentiles
Birth to 24 months: Boys Length-for-age percentiles and Weight-for-age percentiles
Birth to 24 months: Girls Weight-for-length percentiles and Head circumference-for-age percentiles
Birth to 24 months: Girls Length-for-age percentiles and Weight-for-age percentiles

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