Help! My baby isn't following the percentile lines.
What’s normal for breastfed babies?
Growth standards are used to help check that babies are growing well. Your baby's weight can be plotted against a weight-for-age growth chart, which shows how their weight should change over time.
The World Health Organization (WHO) growth standards are based on healthy, exclusively breastfed babies from six countries across five continents. They show how a normal baby grows. There are charts for weight, length and head circumference, each of which should be plotted as the baby grows.
The most common type of growth chart is a percentile chart. To create these charts, the weights of many thousands of healthy babies are recorded and then divided into 100 equal groups. These groups are then plotted on a graph or listed in a table. Percentile charts allow us to compare the weight of one baby with many, many others the same age.
It's important to use the correct growth charts when recording your baby's growth. Older charts were based on a mix of breastfed and formula-fed babies, each with different growth rates. These may still be used in some places, so check that your baby’s growth is being plotted on the WHO growth charts. If your baby record book doesn't contain the WHO growth standards, you may like to print them out and put them in your book.
Do I only need to record my baby's weight?
Your baby's weight is one important measure of their growth, but their length (height) and head circumference will also increase with age.
Your baby's healthcare provider will most likely measure their length and the size of their head when they weigh your baby. They will use charts similar to the ones for weight to record and assess these measurements. This will give you a good idea about your baby's overall growth.
You can view the full collection of WHO child growth standards (including charts and tables for length/height, head circumference and older children) online.
How do I read a growth (percentile) chart?
Growth charts can be difficult to read and understand. Many people misinterpret what they see on the charts. It is the pattern of growth over time that is important, not the growth from week to week.
Understanding percentile lines
3% of healthy babies (3 in every 100) will grow below the bottom line on the chart (3rd percentile), and 3% will grow above the top line (97th percentile).
15% of babies (15 in every 100) will grow below the 15th percentile, and 15% of babies will be above the 85th percentile.
50% of babies (half) will be below the middle line (50th percentile) and 50% will be above.
Does it matter if my baby doesn't 'stick' to a percentile line?
Usually, no. Growth charts are created using the averaged measurements of thousands of babies and so they show 'smoothed' lines. An individual child is unlikely to follow a line exactly.
Your child will grow along their own growth curve which will be marked on the growth chart each time they are weighed and measured. Sometimes this matches up with a percentile line on the chart, but most are between two lines. Sometimes a child will have a period of slower or faster growth that causes them to cross over a percentile line. This doesn't always mean there is a problem. For example, a baby who is born large may have an early period of 'catch-down' growth where they put on weight more slowly than smaller babies. As children get older, they are less likely to cross percentile lines, but it does sometimes happen.
If your child's growth curve suddenly flattens or turns upwards or downwards (and continues that way) it's important to see your doctor. They can look at your child's overall growth and development to check they are healthy.
- World Health Organization (WHO). (n.d.). WHO Child growth standards. https://www.who.int/tools/child-growth-standards/standards
- The Royal Children's Hospital Melbourne. (2013). ‘Is my child growing well?’ Questions and answers for parents.
- Raising Children. (2023). Child growth charts.
