Just like in the fictional Minnesota town of Lake Wobegon, where “all the children are above average,” many parents believe there is something wrong if their breastfeeding baby’s weight isn’t above the 50th percentile. While it is human to want our children to excel, the assumption that babies at a higher weight percentile are healthier or somehow “better” reflects a basic misunderstanding of growth charts and what they mean.
The purpose of a growth chart is to plot a baby’s growth on a series of percentiles, with the average baby at the 50th percentile. What this really means in terms of weight is that out of 100 children, 49 will weigh less and 50 will weigh more. A weight that falls at a higher percentile is not “good” and a weight that falls at a lower percentile is not “bad.” By definition, there will be healthy children at every percentile. Some will be chunky and some will be petite, but their percentile does not necessarily reflect their overall health or growth.
A child at the 5th percentile is not necessarily growing poorly and the child at the 95th percentile is not necessarily growing well. That’s because growth can only be evaluated over time. For example, a preterm baby born very small will likely fall on a low percentile for weight at first, even when he is gaining weight well. Also, if during pregnancy a mother had high blood sugar levels, gained a lot of weight, or received lots of IV fluids during labor, her baby’s birth weight may be unnaturally high. In these situations, after birth a large baby may fall in percentiles to a weight closer to what his genes naturally dictate.1
But parents are not the only ones confused. A U.K. study2 examined both mothers’ and healthcare providers’ perceptions of growth charts, and found that many mothers worried about their baby’s weight gain between checkups and that both mothers and healthcare providers erroneously considered the 50th percentile a goal to be achieved. When babies fell below the 50th percentile, healthcare providers often recommended the mothers give their babies formula and solid foods to try to boost baby’s weight gain to reach this “desirable” percentile. The researchers concluded that healthcare providers need more training on how to assess the growth of breastfeeding babies and how to support breastfeeding rather than undermine it.
Normal growth means a baby is gaining weight at a healthy pace and growing well in length and head circumference. One point on a baby’s growth chart should never be considered in isolation but rather compared to other points. It’s a baby’s growth pattern over days, weeks, and months that provides an accurate picture of how breastfeeding is going. If a baby is growing consistently and well, his actual percentile is irrelevant.
If over time, however, his weight-for-age percentile drops, first it’s important to determine whether the chart is based on breastfeeding norms, as many are not. (Click here for the World Health Organization’s growth charts based on exclusively breastfed babies.) If the chart is based on breastfed babies and the baby’s weight-for-age percentile has dropped, this is a red flag to take a closer look and see if breastfeeding dynamics can be improved.
1Mohrbacher, N. Breastfeeding Answers Made Simple: A Guide for Helping Mothers. Amarillo, TX: Hale Publishing, 2010.
2Sachs, M., Dykes, F., & Carter, B. Feeding by numbers: an ethnographic study of how breastfeeding women understand their babies' weight charts.Int Breastfeed J 2006; 1:29.