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.
Prevalence of teenage pregnancy
The highest rate of teenage pregnancy in the world — 143 per 1,000 girls aged 15–19 years — is in sub-Saharan Africa. Women in Africa, in general, get married at much earlier ages than women elsewhere — leading to earlier pregnancies. In Nigeria, according to the Health and Demographic Survey in 1992, 47% of women aged 20–24 were married before 15 and 87% before 18. 53% of those surveyed also had given birth to a child before the age of 18. Teenage birth rates in African countries (2002) According to data from World Bank, as of 2015, the highest incidence of births among 15-19 years old girls was in: Niger, Mali, Angola, Guinea and Mozambique.