When people move, they bring with them the attitudes and behavior of the places they have left. Rural people who choose to migrate often do so because they want to change their lives for the better. Controlling their own fertility can be an important part of this change. Also, large families may find it harder to move than small families.
Disruption is an especially important force in the case of refugees and displaced persons.
As migrants settle into urban areas, new influences and new social networks change their lives. Urban life erodes the social underpinnings of high fertility, which are much stronger in rural areas. For example, in rural Africa supports for high fertility include polygamous marriages, the high social status associated with bearing many children, a woman's obligation to her husband's parents to bear children, and the use of child labor in agriculture. Adaptation to urban norms may affect a woman's fertility and her child's health if she no longer breastfeeds a newborn child. Breastfeeding tends to postpone the next pregnancy as well as to provide good nutrition to the infant children.