Vietnam has been implementing the policy of fertility decline through the population program, fertility health care
including family planning. Small household size is now encouraged. Together with services of fertility health care, family planning
provided, a lot of popularizing, propagandizing activities for changing behaviors have been organized in order to equip couples
with knowledge and encourage them to carry out the target of family planning. We have of course obtained some certain
success1, however there still exists the problem of couples giving birth to a third child, especially in some geographic regions,
this rate tends to increase. One of the most important reasons for giving birth to a third child arise from the need of Vietnamese
families to have at least one son. Because the son is responsible for caring for old parents, ancestor worship, continuity the
lineage, etc.