By Katherine Barrett and Richard Greene
During the years when the baby-boom generation was being introduced to the population of the United States, the fertility rate equaled about three births for each woman of child bearing age. But since the mid-1960s, when the baby boom ceased, fertility rates have been dropping. By the early 1970s, the fertility rate fell below two births per woman, and it has been declining steadily for at least the last 10 years. Since then, the U.S. fertility rate has been below replacement level—the level that is needed for couples to replace themselves in the population—according to the Population Reference Bureau.