Understanding paediatric growth charts is essential for monitoring the growth and development of children to inform healthcare professionals, parents, and caregivers of the well-being of children. Paediatric growth charts have been created using extensive data from a wide range of paediatric populations in different geographical locations. Through these charts, healthcare professionals can track a child's growth and development over time and intervene when necessary, ensuring optimal development.

This article explores the significance of paediatric growth charts, the interpretation of centile lines, and the use of standardised growth standards, such as those established by the World Health Organization. By understanding these principles, stakeholders can actively participate in promoting the health and well-being of children worldwide.

Who is the ‘paediatric population’?

A population refers to a group of people with specific characteristics.¹ The paediatric population is made up of a number of different subpopulations. For instance, neonates (birth to 1 month), infants (1 month to 2 years), developing children (2 to 12 years), and adolescents (12 to 16 years) as outlined by the Food and Drug Administration (FDA) guidance from 1998.²

These groups differ in body composition (how much of our body is fat, muscle, or bone), biochemistry (the chemical processes that happen within our body), physical size, and physiology (how our body works). In the initial 2 years of life, development and growth happen especially quickly. By 6 months, body weight usually doubles and by the first year body weight is tripled. Additionally, in the first year of life body surface areas doubles.³ Throughout infancy and childhood, the percentage of protein, body fat, and water constantly changes.⁴

Understanding growth in children

Growth refers to physical development as well as the increase in dimensions or size over time. In the context of paediatrics, growth is an essential indicator of the health of a child. Growth can be affected by a variety of factors including –

• Birth weight
• Chronic (long-term) illness
• Gestational age (length of pregnancy of the mother)
• Environmental factors
• Type of feeding – whether the child was formula or breastfed as a baby
• Genetic influence of parents such as parental stature
• Special health care needs⁵

The purpose of measuring growth in children

The main purpose of measuring children stems from the link between high mortality and morbidity and poor growth in early childhood.⁶ Mortality refers to death in particular, the number of deaths resulting from a particular health condition or disease over a certain period of time.

Morbidity refers to whether an individual has a certain health condition or illness, including chronic (long-term) or acute (short-term) illnesses.⁷ Historically, the sufficiency of infant feeding was monitored via regular weighing. Longer term, an index of wellbeing and health was growth in terms of height.

A large range of childhood disorders have been associated with stunted or slow growth. On the other hand, a child who is shown to be growing normally is less likely to have underlying medical issues which may pose detrimental to overall health. Another factor of major underlying surgical and medical disorders is accelerated or slowed head growth. 

Importantly, the rate of growth in the paediatric population can vary with age and sex. Whether a child is growing normally or not can only be assessed through comparisons with measurements that are defined as a normal range in healthy children of the same age and sex. These comparisons are made possible through growth charts.⁶

How are growth charts made?

Growth charts are made using measurements from a large sample of children of different ages. These measurements are used as reference points, which are then connected together between the key points at each age. Thus, forming a visual representation of growth patterns over time. Previously, growth charts were produced manually by hand however, now this can be done digitally through sophisticated mathematical techniques.⁶

What are centile lines?

On growth charts there are many curved lines known as percentile or centile lines which represent the average height and weight of children at a specific age and sex.⁸ Each line at a certain centile shows the height or weight in which a certain percentage of children fall below.

In the growth charts currently used in the UK, there are nine centile lines – 0.4^th, 2^nd, 9^th, 25^th, 50^th, 75^th, 91^st, 98^th, and 99.6^th. The space between each centile line is referred to as the centile space. A more detailed explanation of these centile lines is provided below.

• 0.4^th centile line – 0.4% of children are below this line. This helps identify extremely low cases or outliers
• 2^nd centile line – 2% of children fall below this line. This shows potential underdevelopment or slowed growth in children
• 9^th centile line – 9% of children fall below this line. If the measurement for a child falls at the 9th percentile, it means that their measurement is greater than or equal to 9% of children, but less than 91%
• 25^th centile line – 25% of children fall below this line
• 50^th centile line – 50% of children fall below this line. This line also represents the median, or middle value
• 75^th centile line – 75% of children fall below this line
• 91^st centile line – 91% of children fall below this line
• 98^th centile line – 2% of children fall below this line. This also shows potential overdevelopment or increased growth in children
• 99.6^th centile line – 99.6% of children fall below this line. This shows extremely high cases or outliers⁶

World Health Organization (WHO) growth charts

In April 2006, WHO published growth standards for infants and children up until 5 years of age. The most updated child growth standards are available on the World Health Organization website.⁹ These published results were based on the WHO Multicentre Growth Reference Study which occurred between 1997 and 2003, primary growth data, and data collected from approximately 8500 healthy, breastfed children from different cultural and ethnic backgrounds.

This included children from India, Oman, Ghana, Norway, Brazil, and the United States of America (USA). The purpose of these new growth charts was to produce the best description of physical growth for children from birth to five years of age. The WHO growth charts provide a single international standard, meaning WHO growth charts are accepted and used all over the world.

This ensures consistency and quality in measuring growth in children. Another purpose of these growth charts was to provide a statistical framework to show that breastfed infants are the ideal standard for healthy growth and development.¹⁰ This framework was chosen by the United Kingdom (UK) to construct the UK-WHO growth charts for children under the age of 4 which were introduced in May 2009.¹¹

FAQs

Are these charts appropriate for a child who has been formula-fed or stopped breastfeeding early?

Firstly, it is important to remember that how you feed your baby is a personal choice and there are benefits to both formula feeding and breastfeeding. While the growth charts show how a healthy breastfed child would grow, it would be desirable for a formula-fed child to follow the same healthy pattern. Therefore, yes, these charts would be appropriate for a child who has been formula-fed or stopped breastfeeding early.

There are no centile lines present between birth and 2 weeks, why is this?

During the first two weeks of life, growth patterns show a wide variation as some babies initially lose weight and then regain it. This cannot be captured by a growth chart, instead for the first 2 weeks, weights are compared to the birth weight of the child.

Summary

This article has discussed the construction of paediatric growth charts and the use of centile lines to allow the interpretation of a child's measurements in relation to the wider population. Growth charts can be utilised to identify potential issues in relation to a child's growth and development, allowing for timely intervention if required.

Growth standards developed by WHO provide an international framework for assessing growth and development in breastfed infants, setting an international standard. Through growth charts and standardised growth standards, healthcare professionals, parents, and caregivers can actively engage in promoting the well-being and development of children.