How do statistical organizations define age periods for children?

Neonates, infants, children: what age ranges do these terms refer to?

October 9, 2023

To help understand data about children – such as child health and mortality – statistical organizations classify the ages of babies and children in a more standardized way.

The World Health Organization (WHO) and United Nations Inter-agency Group for Child Mortality Estimation (UN IGME), for example, use the same definitions for various stages of infanthood, childhood, and adolescence.

I have shown these definitions in the visualization below.

Many countries also use the same definitions for their national statistics, but this is not always the case.

In the sections below, I’ve included summaries of how different stages are defined.

Image showing the definitions of different age groups of infants and children.

Infants

As you can see in the visualization, ‘infants’ are defined as those under one year of age.

Within this age period, there are several categories:

28 days to 1 year of age

These definitions are used consistently by the WHO, UN IGME, and IHME. 1

Children and adolescents

In contrast, the term ‘children’ is often used inconsistently and describes children of different age ranges.

To avoid confusion, statistical organizations tend to use the term ‘under-5’s’ to describe children under 5 years of age. 2

The World Health Organization (WHO) and United Nations Inter-agency Group for Child Mortality Estimation (UN IGME) additionally define adolescents as those aged 10 to 19. 3 But definitions for adolescents differ widely and sometimes include people up to much older ages.

Miscarriages and stillbirths

Age periods for fetuses – which are referred to in statistics on miscarriages and stillbirths – are often defined inconsistently between countries and statistical organizations.

For example, the WHO defines miscarriage as the spontaneous loss of pregnancy before 28 weeks of completed gestation. 4

In contrast, the Institute for Health Metrics Evaluation (IHME) defines miscarriage as the “spontaneous loss of pregnancy before 24 weeks of gestation with complications requiring medical care.” 5

Definitions of stillbirths also vary.

For example, the International Classification of Diseases 11th Revision (ICD-11) defines stillbirths as babies born with no signs of life at 22 or more completed weeks of gestation. They also have two sub-categories of stillbirths: ‘early gestation stillbirth’ (at 22 to 27 completed weeks of gestation) and ‘late gestation stillbirth’ (at 28 or more completed weeks of gestation).

In contrast, the WHO and UN IGME define stillbirths as those at 28 or more completed weeks of gestation, which corresponds to what the ICD-11 calls late gestation stillbirths. 6

Due to differences in definitions, miscarriages and stillbirths are not shown in the chart.

Endnotes

  1. United Nations Inter-agency Group for Child Mortality Estimation. (2022). Levels and trends in child mortality: Report 2022. https://web.archive.org/web/20230110001957/https://data.unicef.org/wp-content/uploads/2023/01/UN-IGME-Child-Mortality-Report-2022_Final-online-version_9Jan.pdf World Health Organization. (2022). Neonatal mortality rate (0 to 27 days) per 1000 live births) (SDG 3.2.2) [dataset]. https://web.archive.org/web/20220212084442/https://www.who.int/data/gho/indicator-metadata-registry/imr-details/67
  2. When ‘children’ is not further defined, it is often the case that the term refers to the same age group: of children under 5 years of age. However, this should be verified in each case to make sure that the data is being interpreted correctly.
  3. UNICEF. (2018). Adolescent Health: The Missing Population in Universal Health Coverage. https://web.archive.org/web/20230116115339/https://www.unicef.org/media/58171/file
  4. World Health Organization. (n.d.). Why we need to talk about losing a baby. https://web.archive.org/web/20200714054822/https://www.who.int/news-room/spotlight/why-we-need-to-talk-about-losing-a-baby
  5. Institute for Health Metrics and Evaluation. (2019). Maternal abortion and miscarriage—Level 4 cause. https://web.archive.org/web/20230911090828/https://www.healthdata.org/results/gbd_summaries/2019/maternal-abortion-and-miscarriage-level-4-cause
  6. United Nations Inter-agency Group for Child Mortality Estimation. (2022). Never Forgotten: The situation of stillbirth around the globe. https://web.archive.org/web/20231010181050/https://childmortality.org/wp-content/uploads/2023/03/UN-IGME-Stillbirth-Report-2022.pdf United Nations Inter-agency Group for Child Mortality Estimation. (2023). Stillbirth Definition and Data Quality Assessment for Health Management Information Systems (HMIS). https://web.archive.org/web/20230220150629/https://childmortality.org/wp-content/uploads/2022/10/Stillbirth-definition-and-data-quality-assessment_20221006.pdf

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