This report presents and interprets birth statistics for the United States with particular emphasis on changes that took place during the period 1970-73. Data for the report were based on information entered on birth certificates collected from all states. The majority of the document comprises graphs and tables of data, but there are four short expository sections which summarize trends. These sections examine details of recent fertility trends, changes in completed fertility and total fertility, changing patterns of fertility control, and future trends. The statistics show that by 1973 the U.S. fertility rate had declined to the lowest number ever recorded, and the annual number of births was the lowest since 1945. Major factors influencing this decline were changes in the ages at which women give birth and an emerging preference for smaller families. The greatest declines in fertility were for women aged 40 and older. There was a gradual lengthening in the interval between births for both white and black women. White women under age 30 experienced a higher level of childlessness than women of all other races, a reversal of the pattern of previous decades. (Author/AV)