A note of caution is necessary before discussing the levels and trends in fertility in the various countries and regions and in the world considered as a whole.
Adequate reliable information on the number of births, birth rates and trends in birth rates is available for most of the developed countries but for only very few of the developing countries.
As the vital registration systems in many developing countries, if at all in operation, do not provide reliable data, reliance has to be placed on estimates of birth rates and other relevant information about birth rates as well as other particulars regarding fertility.
In accordance with the recommendation of the World Population Plan of Action adopted at the World Population conference at Bucharest in 1974, the United Nations has undertaken the task of monitoring of population trends.
The following section is based mainly on the reports prepared in 1984 by the Population Division of the United Nations.