Birth rate
The region of Sub-Saharan Africa has the highest birth rate in the world. As of 2016, Niger, Mali, Uganda, Zambia, and Burundi have the highest birth rates in the world. This is part of the fertility-income paradox, as these countries are very poor, and it may seem counter-intuitive for families there to have so many children. The inverse relationship between income and fertility has been termed a "demographic-economic "paradox"" by the notion that greater means would enable the production of more offspring as suggested by the influential Thomas Malthus.
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.