Growth charts – Children’s Dietician Lucy Upton answers common questions about babies’ growth

One of the questions we’re often asked after our baby is born is how much they weighed, and you might have heard people talking about centiles or following a line – but what does all this mean, and how often should your baby be weighed? We asked paediatric dietician and feeding therapist Lucy Upton to answer some common questions about growth and growth charts.  

How do we monitor a baby or child’s growth? 

From birth to 18 years of age, children's growth is tracked and monitored over time using growth charts. You will find these in the back of your personal child health record (‘red book’), and there are specific charts for girls and boys, coloured pink and blue, respectively. Growth charts monitor your child’s measurements, plotting your child’s weight and height, alongside head circumference in the <2s. By monitoring a child’s measurements using these charts over time, we can ensure they follow their expected growth pattern. 

What do the lines on growth charts mean? 

The lines on the growth chart are called centile lines. These curved lines show average weight and height gain, alongside how a child compares to other children of the same age and gender. For example, if your child falls on the 9th centile for their height, they would likely be around the 9th tallest in a class of 100 children of the same age and gender.  Similarly, if they fell on the 75th centile, they would be around the 75th tallest, with 25 children still likely to be taller than them but 74 smaller.  

The centile lines also show periods of time when we expect a child’s rate of growth to speed up and times when it slows down. Rates of growth for children can vary by their age, and periods of time when growth appears to be slower are to be expected. 

It is important to remember that a child’s growth can be healthy and ‘normal’ on any of the centile lines. It’s a myth that all children should fall on the 50th centile, or that the higher the centiles the better for growth.   

How do I know if my child is growing ok? 

When monitoring a child’s growth, health professionals are looking for consistent gain (or increase) following a child’s own centile lines, or within a healthy centile range. For example, if a baby has plotted the 25th centile for weight, we would expect them to continue to follow along this centile or within two centile lines above or below this going forward. Weight for length or height is also reviewed, to ensure a child’s weight gain is considered to be proportional (within a healthy range) compared to their length or height growth (centile). Children do not have to fall on the same weight and length/height centile to have healthy growth. 

It is normal to see some fluctuations, especially to weight centile at times such as: 

• During and after illness 
• When baby becomes more mobile/walking 
• Moving into the toddler years – when the rate of growth slows down comparative to the first year of life 

Health professionals may suggest additional support or intervention if there are concerns about a baby or child’s pattern of growth on a centile chart. Worries about growth generally occur when: 

• A baby or child has drifted or fallen across 2 or more weight centile lines, for instance, from the 50th centile to under the 9th centile* 
• There is a significant difference between a child’s weight and height centile position, for example, 2-3+ centiles different  
• When a child’s Body Mass Index (BMI) is calculated to be low (MI is only used in children over 2 years of age) 

*Be careful with the use of any electronic or app-based centile charts. Some growth chart apps do not use the WHO centile lines and may record your child's growth between the 0-100th centiles, so some parents can worry if their child has fallen from the 20th to the 18th centile, for example. This is not considered to be a drop across two centile lines – a faltering growth diagnosis is measured by the crossing of the WHO centile line positions outlined on the growth charts. 

How often should my child be weighed and measured?

How often your child is weighed depends on how old they are. Frequent weighing, unless under the advice of a health professional, is generally discouraged, as it can sometimes cause unnecessary worry about a child’s weight or growth.  

The table below shows recommended weighing frequency, depending on age 

Age                                         Recommended weighing frequency 

2 weeks* to 6 months            No more than once a month 

6-12 months                            No more than once every 2 months 

Over 1 year                              No more than every 3 months 

More frequent weight checks may be recommended if there are concerns about a child’s growth. 

Length or height measurements are often routinely completed during baby and child health checks.  

*Babies are not plotted on growth charts within the first two weeks of life, as there are unique changes to their weight during this stage and it can be common for babies to lose weight after birth, before regaining it towards 10-14 days of age.