A pediatrician needs to analyze the infant mortality rates. What must be taken as the unit of observation for this purpose?

Answer options

1. A case of death of a child after 28 days of life.
2. A case of death of a child within the first 7 days of life
3. A case of death of a child under one year of age
4. A case of the death of a child during childbirth
5. A case of death of a child within the first month of life