The period of full-term pregnancy does not vary much and its duration is assumed to be nine months. However, in case pregnancy ends prematurely in a spontaneous or induced intrauterine death.

The duration of the birth interval is lengthened by the following additional components: a shortened pregnancy, a small infecundable period, and conception wait as shown in panel B.

Thus it is observed that seven proximate determinants, namely, marriage (marital disruption); onset of permanent sterility; post-partum infecundability; natural fecundability or frequency of intercourse; use and effectiveness of contraception; spontaneous intrauterine mortality; and induced abortion, have been identified as proximate determinants of human fertility.

It is clear that the first two of these seven determinants determine the length of reproductive span and the other five determine the rate of child- bearing.

ADVERTISEMENTS:

Of these seven determinants, five determinants, namely^ marriage (and marital disruption); onset of permanent sterility: post-partum infecundability natural infecundability or frequency of intercourse and spontaneous intrauterine mortality, determine the levels and differentials of natural fertility in various populations.

The model developed by John Bongaarts in 1978 remains one of the most widely used tools for analysing fertility and fertility change. Since the development of Bongaarts framework, a wealth of new data has become available.

After reviewing a large number of new data Stover suggests how some of these new data might be integrated into the proximate determinants model.