So What’s the Big Deal About Growth Curves?

By Barbara Behrmann, Ph.D.

© 2006

Stella’s baby, Sophie, is 4 months old and has had nothing but breast milk.* Although Sophie has been gaining weight steadily, her growth rate has begun to slow down and her doctor seems a little concerned.  Maybe Stella should start giving her some formula, the doctor suggests. Stella had hoped to avoid this, but suddenly she’s worried.  Should she take her advice?

Before I answer that question, let’s back up.  In order to assess a baby’s weight, height, and other aspects of his or her development, health care professionals use a measurement tool known as growth curves.  These curves are used to track an individual child’s development over time, as well as to compare that child to others children of the same age.

Getting Science Backward

Until April of 2006, the curves that health care providers used were based on a sample of babies from white, European immigrant families at a time when breastfeeding was rare, infant formulas were inferior to those today, and solid foods were introduced much earlier than they are now. 

Is this a big deal?  You bet.  Let’s start with an analogy.  First of all, imagine that you haven’t just had a baby, causing you, perhaps, to rank sex just below emptying the garbage disposal.  Now imagine that researchers are interested in studying adult sexual behavior.  They survey a group of men and women, apparently healthy, and discover that few of them express much interest in sex.  Based on this survey, researchers determine a “normal” level or range of sexual interest.  Now imagine that you read these findings, but they don’t seem to apply to you.  You are very interested in sex.  Are you sexually obsessed?  Is there something wrong with you?  You begin to worry.

Unfortunately, what you didn’t know was that most of the people surveyed were on anti-depressant medication.  And a common side effect of the medication is a compromised libido.  In reality, then, your sexual desires are normal.  There is nothing wrong with you. This is the standard against which people whose physiology has been chemically altered should be measured.  Not vice-versa.

While it’s hard to imagine that such a poorly designed study could actually take place, this is what it used to be like when you took your baby in for a check up.  Breastfeeding, not formula feeding, is the biological norm.  But your exclusively breastfed baby would have been compared to children whose development was not based on normal biology.

Formula fed babies have different patterns of weight gain compared to breastfed babies.  Exclusively breastfed babies often start out gaining weight more quickly than formula-fed babies, but after a few months this pattern reverses so that formula-fed babies gain more quickly.  By incorrectly using formula feeding as the biological norm, doctors may end up expressing concern that an exclusively breast-fed baby isn’t growing as rapidly as he “should be” or that she is falling off a particular growth curve.  In some cases, doctors may even recommend supplementing with formula or introducing solids, when, in fact, the baby was perfectly healthy all along – e.g., Sophie.

Enter New Growth Curves

The good news is that thanks to a 1997 study initiated by the World Health Organization, we now have new Child Growth Standards with all data coming from a sample of exclusively breastfed babies.   And because we now know the growth trajectory of exclusively breastfed babies, we know that it’s perfectly normal for Sophie’s growth to have slowed.  Should Stella supplement Sophie with formula?  Not likely. 

In fact, formula-fed babies may be growing too much.  The growth charts don’t just apply to breastfed babies; they apply to all babies.  In the case of formula-fed babies in developed countries, the standards can be used to determine when a baby is being fed too much.   With obesity a growing problem in this county (pun only partly intended), the new standards can help identify children who may be headed in the direction of becoming overweight or obese before it becomes harder to prevent or control. 

This leads to another benefit of the new growth standards; they are just that, standards.  They don’t simply describe a child’s growth compared to other children, but they provide standards for assessing the physical growth, nutritional status and motor development in all children from birth to age five.   And because these new standards are based on a sample of children from six different countries around the world, they show that with proper feeding practices, adequate health care and a healthy environment, children from around the globe have the potential to develop within the same range of height and weight.

“The WHO Child Growth Standards are a major new tool for providing the best health care and nutrition to all the world’s children,” said Dr. Adenike Grange, President of the International Pediatric Association (IPA), in an April 27, 2006 press release.

*Stella and Sophie represent a hypothetical example. 

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Barbara L. Behrmann, Ph.D. is a writer, researcher, and author of The Breastfeeding Café: Mothers Share the Joys, Secrets & Challenges of Nursing, University of Michigan Press, 2005. She is a frequent speaker around the country and is available for talks, readings, and conducting birthing and breastfeeding writing circles. The mother of two formerly breastfed children, Barbara lives in upstate New York.