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
Worldwide, teenage pregnancy rates range from 143 per 1000 in some sub-Saharan African countries to 2.9 per 1000 in South Korea. In the U.S., 82% of pregnancies in those between 15 and 19 are unplanned. Among OECD developed countries, the U.S., the UK and New Zealand have the highest level of teenage pregnancy, while Japan and South Korea have the lowest in 2001. According to UNFPA, “In every region of the world – including high-income countries – girls who are poor, poorly educated or living in rural areas are at greater risk of becoming pregnant than those who are wealthier, well-educated or urban. This is true on a global level, as well: 95 per cent of the world’s births to adolescents (aged 15–19) take place in developing countries. Every year, some 3 million girls in this age bracket resort to unsafe abortions, risking their lives and health.”