David, H. P., & Baldwin, W. H. (1979). Childbearing and child development: Demographic and psychosocial trends. American Psychologist, 34(10), 866-871.
http://dx.doi.org/10.1037/0003-066X.34.10.866
A major trend in the US is the continuing decline in fertility. A steadily decreasing proportion of births are reported by married women as being unwanted at the time pregnancy was discovered. Currently marriage, 1st birth, and family formation are longer delayed. Preference for a smaller family is stronger. Increasing proportions of young wives are childless, while the birth rate for firstborn children is rising for women in their late 20's and early 30's. Improved control of family size is partly a function of effective contraceptive methods but probably is more closely related to higher levels of motivation. Births to women under age 20 now comprise a higher proportion of total births and are of increasing societal concern. International trends are discussed. (7 ref) (PsycINFO Database Record (c) 2016 APA, all rights reserved)