The above shows fertility rate by country. Fertility rate seems to be loosely correlated with the wealth/development of a country. A particular driving force behind these numbers is infant mortality; in places where infant mortality is lower, parents can be more assured that the kids they have will survive, and so feel less pressure to have more kids in order to increase the chances that some will survive. Thus, quality of life is one of the major driving factors behind fertility rates, although it may be the opposite of what some expect. As a country gets wealthier and more developed, people tend to have less children, and population growth tends to slow.