The ability of couples to plan the size of their family and the timing of births has important sociological implications for both individual families and society as a whole. Women's roles and labor-force participation, the socialization of children, social and economic development, and ultimately the ability of the earth to sustain human life are all affected in one way or another by the ability of couples to practice family planning and the success with which they do so. In the United States, women expect to complete their childbearing with an average of 2.2 children per woman (Abma et al. 1997), and, on average, women have 2.0 births over their lifetime (Ventura et al.). Throughout the world, the average number of children desired varies from about two in most industrialized nations to between six and eight in some African nations (Alan Guttmacher Institute 1995). In order to limit lifetime births to...