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20Th percentile baby


Percentiles and What They Mean

Written by Steven Jerome Parker, MD

Q: My baby is small but my pediatric provider says she is "following the curve" so he is not worried. What does that mean? I'm still worried!

A. If your baby is "following the curve" of the growth chart, she's paralleling one of the percentile lines on the chart, and the odds are good that her caloric intake is fine, no matter how much or how little milk she seems to be drinking.

On the other hand, if she is "falling off the curve," she's dipping below two or more percentile lines on the growth chart, and she may have inadequate nutritional intake. This could represent a real problem.

Growth Charts: How They Work

There are separate growth charts for weight, height, and head circumference.

These simply represent the average weight, height, or head circumference of a bunch of normal children. You will see the percentile lines on the chart running parallel to each other. The percentile lines include 5%, 10%, 25%, 50%, 75%, 90%, and 95%. (For more information, see the CDC's web site: www.cdc.gov/growthcharts/).

If a child's weight is at the 50th percentile line, that means that out of 100 normal children her age, 50 will be bigger than she is and 50 smaller. Similarly, if she is in the 75th percentile, that means that she is bigger than 75 children and smaller than only 25, compared with 100 children her age.

What Growth Charts Tell Us

The growth percentiles by themselves don't say much. What really matters is the rate of growth:

  • A normal rate of growth means the child's growth points closely follow a percentile line on the chart.
  • We usually don't worry about insufficient (or excessive) growth until a child's growth rate has crossed at least two percentile lines (e.g., from above the 90th percentile to below the 50th).
  • If a child's weight, height, or head size is below the 5th percentile, it's important to see if her growth points have always paralleled the 5th percentile line -- which would mean her growth rate is normal -- or if she is suddenly falling further behind, which is more concerning.

To see if your child is too skinny or overweight, there is a "weight for height" chart or a "BMI" index. These tell if your child's weight is close to what it should be, given her height.

How to Tell If Growth Could Be a Problem

One of the first signs that a child is not getting enough calories is when her weight increases at a much slower rate than her height and begins to fall below two percentile lines.

  • Depending on the extent of the poor caloric intake, the child's height could become "stunted," that is, the height begins descending on the growth chart.
  • If the lack of nutrition is severe and continues for an extended period of time, the head growth slows down, indicating that there are not enough calories for the brain to grow at a normal rate.

Similarly, a steady increase in weight, while the child's height increases at a much slower rate, indicates she may be putting too much extra meat on her bones. This can be a good thing or an early sign of a risk of obesity.

Tips:

Put the growth chart into context. No child's growth and development is always so smooth and perfect like the lines of the chart. Kids bounce up and down the growth charts, depending on appetite, feeding issues, illnesses, brief feeding strikes, etc.

Consider other signs of good health. Does your child appear otherwise happy and healthy? Is she making nice developmental progress? If the answers are yes, a problem is less likely.

When to Worry

If your child's growth rate slows down (weight, height, or head size) and she falls below two percentile lines, then you should explore the reason for the poor growth.

Dr. P's Pearl

Don't obsess about every up and down of your infant's growth chart. It's only potentially a problem when there is a persistent downward trend, usually lasting many months.

Understanding baby growth charts | Pregnancy Birth and Baby

Understanding baby growth charts | Pregnancy Birth and Baby beginning of content

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Baby or infant growth charts show how your child is growing. It's important not to compare your baby's size with that of other babies since this may be misleading. The most important thing is that your baby is healthy, happy, and growing appropriately.

What is an infant growth chart?

An infant growth chart helps you, your doctor and other health professionals keep track of how your baby is growing.

Your baby’s growth is a good indicator of their overall health and nutrition. This is done by comparing your baby's growth with that of other babies of the same age. There are different charts for:

  • males and females
  • infants and older children

Growth charts record changes in your baby's measurements, including their:

  • length (height)
  • weight
  • head circumference

These measurements are recorded on the chart so you can see how they change over time. On the vertical (up-and-down) axis is the measurement; on the horizontal (side-to-side) axis is the baby's age.

There will probably be a growth chart in your child's personal health record. Depending on where you live, this record is known by different names. In New South Wales, it is the Blue Book. In Queensland, it is the Red Book. Your child and family health nurse or doctor may also keep a growth chart.

Infant growth (aged 0 to 2 years) is usually calculated using the World Health Organization's (WHO) growth standards.

Most states and territories use growth charts based on those from the US Centers for Disease Control.

What are percentiles?

Like adults, babies come in all shapes and sizes. The growth charts show this by using 'percentiles'. Below are some examples:

  • A baby on the 50th percentile for weight is right in the middle of the normal weight range: 50% of babies their age are lighter, and 50% are heavier.
  • A baby on the 5th percentile weighs less than 95% of other babies of that age.
  • A baby on the 90th percentile weights more than 90% of other babies that age.

Some babies will always be small. Others will always be large.

All babies grow at different rates, and 'normal' growth varies a lot. The important thing is that your baby continues to grow at a similar rate.

The WHO's infant growth chart for girls aged 0 to 2. The WHO's infant growth chart for boys aged 0 to 2.

How are the growth charts used?

Growth charts will help you track how your baby is growing by showing normal growth curves (i.e., always increasing). You can plot your baby’s growth to see if it follows a similar pattern to other babies on that percentile.

Your baby is weighed and measured at birth and then when they are 2 weeks old. After that, their growth is best tracked by measuring them every month until they are 6 months old. Don't worry if their weight goes up and down a bit from day to day — this is normal.

Growth charts are used until your child turns 18.

You can talk to your child health nurse or doctor about other health checks to make sure your child is growing and developing normally.

How will my baby be measured?

Special infant scales are used to weigh babies under 2 years old. Newborns lie down on these scales. It’s more exact to weigh babies with no clothes on until they are 12 months.

After they turn 2, they are measured standing up in light clothes. You baby's head circumference is measured using a tape measure.

If your child was born prematurely, their age is 'corrected'. This means their age is adjusted to account for the number weeks that they were born prematurely. This is done by taking the number of weeks early they were away from their birth age. This corrected age is recorded on all their growth charts. This will continue until they turn 2 years old.

When should I be worried?

It’s important to measure a baby’s growth to see if they are healthy and developing properly. Parents are often worried that their baby isn't growing fast enough. However, it's not the only way to tell if they're healthy.

All babies lose some weight in the week after birth. They usually regain this weight by 2 weeks. Most babies double their birth weight by 4 months.

Male babies usually triple their weight by 13 months. Female babies usually triple their weight by 15 months.

There is unlikely to be anything wrong if your baby:

  • has at least 5 very wet nappies each day
  • has pale urine (wee)
  • does well-sized, soft poos
  • has good skin colour and muscle tone
  • is meeting other developmental milestones

Weight gain can be affected by an infection or vomiting. If you are ever worried, talk to your child and family health nurse or doctor.

If your baby’s growth percentile changes a lot – by 2 major percentile lines - talk to your child and family health nurse or doctor. They will assess the child's growth trend to see if there is any reason to be worried.

Remember, don't compare your baby’s growth to that of other baby’s. The important thing is that they continue growing following the same percentile.

Where can I get more information about baby growth charts?

If you have any questions about your baby's growth or development, you can call Pregnancy, Birth and Baby on 1800 882 436. Or see your child's doctor or early childhood nurse.

Speak to a maternal child health nurse

Call Pregnancy, Birth and Baby to speak to a maternal child health nurse on 1800 882 436 or video call. Available 7am to midnight (AET), 7 days a week.

Sources:
Australian Breastfeeding Association (Baby weight losses and weight gains), World Health Organization (Child growth standards), National Children’s Digital Health Collaborative (Child Digital Health Record Digital Baby Books), Healthy Kids for Professionals (Guide to accurately weighing children using infant scales), Healthy Kids for Professionals (Guide to accurately weighing children using standing scales), Child and Adolescent Health Service (Growth – birth to 18 years), The Royal Children's Hospital Melbourne (Clinical Practice Guidelines: Slow Weight Gain)

Learn more here about the development and quality assurance of healthdirect content.

Last reviewed: July 2022


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Need more information?

Growth charts for babies & children | Raising Children Network

Child growth charts give a guide to how well children are growing. Growth usually follows a typical pattern, which is influenced by genes and environment.