Birth rate
According to the CIA's "The World Factbook", the country with the highest birth rate is Niger at 6.49 children born per woman and the country with the lowest birth rate is Taiwan, at 1.13 children born per woman.
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.