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.
Teenage pregnancy
On the other hand, the teen birth rate is very high in Bulgaria and Romania. As of 2015, Bulgaria had a birth rate of 37/1.000 women aged 15–19, and Romania of 34. The teen birth rate of these two countries is even higher than that of underdeveloped countries like Burundi and Rwanda.
Many of the teen births occur in Roma populations, who have an occurrence of teenage pregnancies well above the local average.