Babies come in all colors, shapes, and sizes due to lots of factors including genes, level of activity, and even gender. Thus, it can be quite hard for a pediatrician to assess a baby's growth as normal just by looking at him. To truly assess a child's growth and development, pediatricians use growth charts such as the baby height percentile.
What are growth charts? WHO growth charts are tools used by doctors to monitor a child's growth and development over time. These charts are based on research done by the World Health Organization on thousands of children around the world living in optimal environments. The data on their rate of growth for height, weight, and head circumference were gathered over time and set in a graph, showing how babies should grow if they are provided optimal conditions. In using WHO growth charts like the baby height percentile, doctors are able to do two things. One, they are able to compare a child's height, weight, and head circumference to other children who are of the same gender and age. Second, and more importantly, they are able to keep track of a child's rate of growth and see if it follows a regular pattern.
Often, parents focus more on a single point in the chart, particularly where their child is at the moment. In addition, many are of the belief that a higher percentile means a healthier baby. However, when it comes to these types of growth charts, the "score" is not what makes a child healthy and normal. Instead, the score is simply a means of establishing what a child's growth pattern is.
So, how does that work? When using a baby height percentile, for example, a doctor would need to plot the baby's height as he grows over time. Looking at only one entry in the chart will tell him nothing about the child's health. This is because a baby's height is influenced by several factors, not just what he eats and drinks. A baby whose parents are only 5'2" cannot be expected to have a 90th percentile on the baby height percentile chart. After all, the chart is based on the average baby height of his peers. Plus, there will be a larger number of babies his age that are taller than him just like there are probably a larger number of adults taller than his parents. Thus, a doctor will not be necessarily concerned if a baby has a low "score" on the baby height percentile, or any growth chart for that matter. What will interest him, instead, is looking at several points in the chart which plot the baby's height throughout several months. These points should, more or less, all be in the same percentile - steady as she or he grows. If a baby was in the 40th percentile throughout January until May then suddenly went down to the 10th percentile in June and went even lower in July, this might be an indication that there is something wrong and the doctor will need to do further evaluation.
Another important interpretation of the results that doctors do is to compare the child's growth measurements against each other. A baby's height and weight should be proportional. A child who scores a 90th percentile in weight and scores a 10th percentile in height probably weighs more than he or she should. In the same way, a child who plots high on the chart for height and low on the chart for weight may weigh less than he should.
When it comes to growth charts like the baby height percentile, parents should always be aware that how their child "scores" is less important than what his growth trend is like. Higher is not always better. And growth trends don't happen overnight.