The early 1970's was a period of rapid decline for all fertility indicators in the United States. This paper explores some of the reasons for this decline. Data from a National longitudinal survey of young women are used to examine changes in expectations for lifetime births from 1971 to 1973. These young women decreased their birth expectations substantially over this two-year period from an average of 2.7 to 2.4 births per woman. The relationship of changes in birth expectations to social and demographic characteristics of the woman were explored. The analysis of these longitudinal data showed that expected family size fell dramatically for all women regardless of age, marital status, educational levels, race, age at marriage, current family size, or labor force status. Attitudes toward women's role and family financial status as measured in this research had no significantly systematic impact on young women's family size expectations. Concern for population growth did show a substantial effect on reducing expected family size. The evidence in this paper suggests that a strong consensus has developed that families in the United States should be limited to two children. (Author)