Wednesday, 6 October 2010

Which growth chart to use?

In the past few months, I have happened to talk with three different mothers who told me about their breastfed children's growth "slowing down" around 4 months - the baby's weight percentile dropping and the baby slipping down the growth curve. Somewhat fortunately, all of these mothers were told by their pediatricians that this was "common" or "normal", and none of the pediatricians pushed supplementation or were very aggressive about starting solids.

Unfortunately, while the pediatricians were right not to change the baby's diet, they were wrong in giving moms the impression that their child's growth slowing - while perhaps "common" - was "normal". In fact, they were wrong in giving moms the impression that it was slowing at all! And once that idea is planted in a mother's head, it's hard to erase the underlying anxiety she might have, despite reassurance to the contrary, that her milk is no longer quite keeping up with her baby's needs.

The fact is, many pediatricians' offices still use growth charts developed in 1977, based on a small sample of babies in Ohio who were primarily formula fed. Similarly, even the 2000 Centers for Disease Control (CDC) growth charts are based on a sample of mixed breast/formula feeders. Formula fed babies grow more slowly than breastfed babies in their first few months of life, then begin to grow more quickly than breastfed babies. When we chart breastfed babies on the formula fed growth chart, it makes breastfed babies look nice and high on the chart for the first few months, and then start to look like they are faltering.

What does it look like when breastfed babies are tracked on charts that accurately reflect their growth? To do that, the newest World Health Organization (WHO) growth charts are a far better choice than any of the CDC charts. The WHO charts are based on a worldwide sample of infants who received optimal breastfeeding and complementary feeding.

This article from the Journal of Nutrition does an excellent job of discussing some of the differences between the CDC and WHO growth charts. They have several great illustrations as well to help you visualize how the growth charts differ:

This chart shows the difference between weight-for-age curves in boys ages 0-60 months. You can see how around 4-6 months, the CDC chart line crosses over the WHO line and generally stays above - sometimes quite high above - the WHO line up through age 5.

I like this chart even better, which shows how an average infant from the WHO sample would track on each chart. A baby who tracks normally on the WHO chart (staying fairly even in growth after an initial drop) looks very different on the CDC chart: after an initial rise the baby appears to slowly fall down the growth curve from the age of 2 months on.

One of the moms I talked to went back and plotted her children's growth on the WHO charts and was pleased to see that all of a sudden, instead of slipping down the chart, they were tracking beautifully along the growth curves. She knew all along that they were healthy and feeding well, but it's always nice to have it confirmed that the charts were wrong - and mom was right.

Happily, the CDC is now formally recommending that all clinicians switch to the new WHO growth charts for ALL infants and toddlers up to 2 years of age. (Note that this means not just breastfed babies - the CDC recognizes that those charts reflect optimal infant growth, and that the more rapid growth of formula fed babies is a potential cause for concern.) If you have kids, do you know which charts their pediatrician or family doc is using? Do your care providers know about the CDC encouraging the growth chart switch?

P.S. Let's also keep in mind the relative importance of growth charts. I've had some great conversations in breastfeeding-related courses about the overall silliness of the American obsession with having every baby "above average" on the growth charts. It's as if scoring 95th percentile on the growth chart is like getting an A on an important test. Growth charts are tools to be used in conjunction with other indicators of a baby's health and intake, they do not reflect the normal growth of every child, and it is just as normal and healthy for a baby to consistently be in the 5th percentile as in the 95th. Phew! I've said my piece.