Lowering the birth rate requires education about family planning, birth spacing and, of course, access to birth control. Encouraging the use of birth control is sometimes difficult due to religious prohibitions or superstitious or paranoid beliefs (some people may believe that a medication, such as a birth control pill, is actually being used by a foreign government to sterilize people). Other times, it’s because of a lack of money or political will.

Age structure is also a factor. Most childbearing is done by women between the ages of 15 and 49. So if a population has a large number of young people just entering their reproductive years, the rate of growth of that population is sure to rise.

The population in these areas is growing quickly as the birth rate is high and life expectency is increasing. Most of the countries in Sub Sahara Africa and the middle east still have a total fertility rate greater than 4 children per woman. A total fertility rate of 2.1 children per women would cause zero population growth.

Fertility rates are declining and this trend is expected to continue over the next fifty years causing the world population to eventually stabilise (probably between 8 and 12 billion), however the rate of decline is unknown. According to United Nations estimates, if the total fertility rate of almost every country reached 2.1 children per woman, the world population would be 9.4 billion by 2050. If worldwide fertility only declined to 2.6 children per woman, the world population in 2050 would be 11.2 billion (almost double today's value).