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.
Birth rate
The United States population growth is at an historical low level as the United States current birth rates are the lowest ever recorded. The low birth rates in the contemporary United States can possibly be ascribed to the recession, which led women to postpone having children and fewer immigrants coming to the US. The current US birth rates are not high enough to maintain the size of the U.S. population, according to The Economist.