Registered births are recorded in statistical bulletins which provide a rich source of information. Births are counted on the basis of many different characteristics: parents' marital status and nationality, sex of the child, twin births, etc.

Information on the mother's age is used to calculate annual fertility indicators, such as the total fertility rate expressed as a total number of children per woman.

Completed cohort fertility is also calculated every year. For example, women born in 1970 were 34 years old in 2004. We know how many children they have had before age 34 and we can estimate how many children they will have during their reproductive life.