Table 1.

Definitions of stages of early life

Perinatal Period	22 completed weeks of gestation to Day 7 of postnatal life
Neonatal Period	Birth to Day 28 of postnatal life
Infancy	Birth to 1 year of age
Childhood	1 year of age to 10 years of age
Adolescence	10 years of age to 19 years of age

The data in this table are as defined by the World Health Organization. The perinatal period is defined as 22 completed weeks of gestation to Day 7 of life; the neonatal period, as up to 28 days of life; infancy as up to one year of age; childhood as year 1 to 10; and adolescence from 10 years to age 19.

There is variation worldwide in how these stages of early life are defined. Some would define ‘young people’ as those age 24 or less. In the United States, childhood is as a whole defined as going to age 21.