Birth rate
As of 2017, Niger has the highest birth rate in the world with 49.443 per thousand people. 
Japan has one of the lowest birth rates in the world with 8 per thousand people.
While in Japan there are 126 million people and in Niger 21 million, both countries had around 1 million babies born in 2016.
Income and fertility
Income and fertility is the association between monetary gain on one hand, and the tendency to produce offspring on the other. There is generally an inverse correlation between income and fertility within and between nations. The higher the degree of education and GDP per capita of a human population, subpopulation or social stratum, the fewer children are born in any industrialized country. In a 1974 UN population conference in Bucharest, Karan Singh, a former minister of population in India, illustrated this trend by stating "Development is the best contraceptive." Many countries are experiencing a rather weak correlation with income and fertility rate within a given household. Families with a higher income produce a lower number of children resulting in a low fertility rate whereas families with lower income produce more children with a higher fertility rate. Total fertility rate is specifically the number of children who would be born per woman if she were to pass through the childbearing years bearing children according to a current schedule of age-specific fertility rates. In developing or less developed countries, families need their children for labor and for economic support in the future. Many countries do not have proper pension policies, children are needed in order for the parents to have financial support in their old age.