Family planning means to have children in a desired number, each child at a desired time. Although the parental desire in this regard may be different in individual families, a more or less uniform pattern of reproduction would emerge from practicing family planning, since this need is conditioned by life circumstances that are rather common to all members of the society. Thus, if an appreciable fraction of a population practices it, a change in demographic trends, namely, decline in variances would be expected not only in the number of children per family but also in birth order and parental ages in live-birth data. As family planning is usually used to limit family size, a second sign would be decline in the mean number of children and the mean birth order, while the mean of the parental ages may scarcely be affected.
The purpose of this paper is to review the
Matsunaga E. Possible Genetic Consequences of Family Planning. JAMA. 1966;198(5):533-540. doi:10.1001/jama.1966.03110180077023