Infant Growth Charts

Well-child visits with the pediatrician almost always begin with taking the baby’s weight, height and head circumference measurements. The health care professional then plots those numbers on a growth chart and shows you where your child is on the chart, how your child’s growth is progressing, and whether the numbers fall in a higher or lower percentile on the growth curve than previous measurements. These measuring sessions either provide parents with reassurance if the child is in a particular percentile or growth curve, or spark a lot of worry if a child is not. How valuable is this tool for measuring infant growth and determining whether or not the child’s growth needs improvement?

Until recently, the international growth charts were based on data collected in the 1970s in the United States largely from babies fed infant formula and not breast milk. Subsequent studies showed that the charts did not accurately reflect the general growth curve of predominantly breastfed babies, whose weight rises more steeply than the curve in the early weeks, and may dip slightly after the three-month mark. These discrepancies led to concerns that health care professionals might recommend supplementation or cessation of breastfeeding when those measures simply were not warranted. Unfortunately there is a dearth of information regarding when and how to intervene with respect to weight gain. Even in situations when some intervention clearly is necessary, it would be appropriate and advisable to recommend additional breastfeeding support and other methods that interfere the least with the breastfeeding relationship.

In response to the discrepancies in the growth patterns of formula-fed and breastfed babies, the World Health Organization (WHO) undertook a new study of 8,440 babies in six countries representing various regions of the world: Brazil, Ghana, India, Norway, Oman, and the United States. The babies’ mothers did not smoke during pregnancy or after the birth, and they intended to breastfeed exclusively for at least four months (the recommendation at the time; now the recommendation is six months of exclusive breastfeeding). The six-year WHO Multicentre Growth Reference Study (MGRS) culminated in 2003 and resulted in the publication of several new growth charts in April 2006 (complete publication of the WHO Child Growth Standards is available on Amazon.com):

Length/height for age (recumbent/lying-down length or standing height)
Weight for age
Weight for length
Weight for height
Body Mass Index for age (BMI for age)
Motor development milestones for the six gross motor milestones: sitting without support, standing with assistance, hands and knees crawling, walking with assistance, standing alone and walking alone.

Charts or tables are for boys or girls and may refer either to percentiles or “z-scores.” I’ve only ever had a pediatrician use the percentile chart, but I was curious what the z-score charts mean. Perhaps the mathematically inclined will understand the explanation that a z-score or “standard deviation score” is defined as “the deviation of an individual’s value from the median value of a reference population, divided by the standard deviation of the reference population (or transformed to normal distribution).” Basically this is the number of standard deviations a data point is away from the average.

Medical professionals and parents in the United States may wish to note that the Center for Disease Control pediatric growth charts were developed in the year 2000 and do not reflect the WHO child growth standard. The CDC website says:

The Department of Health and Human Services (CDC and NIH) and the American Academy of Pediatrics convened an expert panel in June [2006] to consider using the new WHO charts versus the CDC charts. The panel compared the 2000 CDC growth charts to the new WHO charts and examined how U. S. children might be assessed differently using the two references. Guidance will be developed for appropriate use of these growth charts for monitoring growth within the US Population.

As to whether the 2000 CDC growth charts are appropriate for exclusively breast-fed babies, the CDC says:

The 2000 CDC growth charts can be used to assess the growth of exclusively breast-fed infants, however when interpreting the growth pattern one must take into account that mode of infant feeding can influence infant growth. In general, exclusively breast-fed infants tend to gain weight more rapidly in the first 2 to 3 months. From 6 to 12 months breast-fed infants tend to weigh less than formula-fed infants.

The 2000 CDC Growth Chart reference population includes data for both formula-fed and breast-fed infants, proportional to the distribution of breast- and formula-fed infants in the population. During the past two decades, approximately one-half of all infants in the United States received some breast milk and approximately one-third were breast-fed for 3 months or more.

The lesson in all of this? If a mother is being told that her exclusively breast-fed baby needs supplementation, she should ask further questions about which chart is being used to monitor her baby’s growth and whether that chart is appropriate for an exclusively breast-fed baby. It might be helpful to print out the appropriate WHO chart to discuss with the baby’s pediatrician.

Even now infant growth charts are relied upon too heavily to monitor infant growth, and that reliance is resulting in inappropriate recommendations by health care professionals. A recent study in the United Kingdom concluded:

Babies were weighed more often than officially recommended, with weighing and plotting being at the core of each clinic visit. The plotted weight chart exerted a powerful influence on both women’s and health visitors’ understanding of the adequacy of breastfeeding. They appeared to rate the regular progression of weight gains along the chart centiles more highly than continued or exclusive breastfeeding. Thus weighing and visual charting of weight constituted a form of surveillance under the medical gaze, with mothers actively participating in self monitoring of their babies. Interventions, by mothers and health visitors, were targeted towards increasing weight gain rather than improving breastfeeding effectiveness. Improvements in training are needed for health visitors in weighing techniques, assessing growth patterns – particularly of breastfed babies – and in giving information to women, if the practice of routine weight monitoring is to support rather than undermine breastfeeding.

Sachs, Magda, Fiona Dykes and Bernie Carter. “Feeding by numbers: an ethnographic study of how breastfeeding women understand their babies’ weight charts.” International Breastfeeding Journal (2006): 1-29.