RESUMO
During the past decade, family-planning programmes have been conducted on the assumption that developments in the field of contraception (e.g. hormonal contraceptives and intra-uterine devices) had reached a stage of considerable technical perfection. Enough information has now been accumulated, however, to indicate that this assumption was not fully justified; the high drop-out rates from these programmes observed under different conditions indicate that there is an urgent need for further improvements of the existing methods and for the development of such methods and for the development of new methods based on different approaches. A pre-requisite for the development of such methods is a greatly improved knowledge of the physiological factors influencing the various steps of the reproductive processes in the human species. In an attempt to focus attention on the various steps which are susceptible to controlled interference, a brief review is given of some of the present concepts of the regulation of spermiogenesis, ovulation and the menstrual cycle, sperm capacitation, fertilization, tubal passage, zygote and blastocyst formation, implantation and early embryonic development. It is concluded that the reproductive processes are indeed subject to intricate biochemical and hormonal regulatory mechanisms and that the different phases of these processes do offer a variety of possibilities for hormonal, pharmacological and perhaps also immunological interference. (AU)
