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 standards1 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
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3% of babies (3 in every 100) will be below the 3rd percentile, and 3% of babies will be above the 97th percentile.
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15% of babies (15 in every 100) will be below the 15th percentile, and 15% of babies will be above the 85th percentile.
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50% of babies (half) will be below the 50th percentile and 50% of babies will be above the 50th percentile.
Does it matter if my baby doesn't 'stick' to a percentile line?
Usually, no. Percentile charts are created using the averaged measurements of thousands of babies and so they show “smoothed” growth curves. An individual child shouldn't be expected to follow a curve exactly. They can and do grow faster or slower at times.
Crossing percentile lines is actually very common, especially in the first 6 months:2
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About 3/4 of babies cross weight-for-age percentile lines over the first 6 months.
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More than 1/3 of babies move up or down two percentile lines.
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From birth to 6 months, larger babies tend to show 'catch-down' growth, where they may put on weight more slowly than smaller babies.
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As children get older, they are less likely to cross two percentile lines, but it does sometimes happen.
If your baby continues to have low weight gains or drops percentiles at a faster rate than expected, it's important to see your doctor.
© Australian Breastfeeding Association October 2022
- World Health Organization (WHO). (n.d.). WHO Child growth standards. https://www.who.int/tools/child-growth-standards/standards
- Mei, Z., Grummer-Strawn, L. M., Thompson, D., & Dietz, W. H. (2004). Shifts in percentiles of growth during early childhood: analysis of longitudinal data from the California Child Health and Development Study. Pediatrics, 113(6), e617-e627.
