The time of the family life-cycle between the time of its formation and the time the last child leaves home has, in historical terms, been lengthening in all societies, the main reason being the decline of mortality. Combined with an early age at marriage and with a longer period of schooling and training for children, the decline of mortality means an increase in the duration of the central phase of the family life cycle, which is still true in most societies.
An average woman in Asia, Africa or Latin America will marry or live in consensual union before she reaches her twentieth birthday, have a first child soon, continue her child-bearing period in her thirties and still be child-rearing during her forties. During this 25- to 30-year period, her mortality risks have diminished, as well as those of her husband.