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.
Demographics of Bangladesh
Bangladesh has the highest population density in the world, excluding a handful of city-states and small countries with populations under 10 million, such as Malta and Hong Kong. The total fertility rate (TFR) has been reduced by more than two thirds since Independence. Current TFR in Bangladesh is 2.1 which means that women have 2.1 children on average in their lifetime. At this TFR and without migration, country's population will eventually be neither growing nor shrinking, once the top of its age pyramid fill in.
Most of the demographic statistics below are from the CIA World Factbook, unless otherwise indicated.