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.
Sub-replacement fertility
As of 2010, about 48% (3.3 billion people) of the world population lives in nations with sub-replacement fertility. Nonetheless most of these countries still have growing populations due to immigration, population momentum and increase of the life expectancy. This includes most nations of Europe, Canada, Australia, Brazil, Russia, Iran, Tunisia, China, the United States and many others. In 2015, all European Union countries had a sub-replacement fertility rate, ranging from a low of 1.31 in Portugal to a high of 1.96 in France. The countries or areas that have the lowest fertility are in developed parts of East and Southeast Asia: Singapore, Macau, Taiwan, Hong Kong and South Korea. Only a few countries have had, for the time being, sufficiently sustained sub-replacement fertility (sometimes combined with other population factors like higher emigration than immigration) to have population decline, such as Japan, Germany, Lithuania, and Ukraine. As of 2016, the total fertility rate varied from 0.82 in Singapore to 6.62 in Niger.