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.
Legitimacy (family law)
It is notable that traditionally-conservative Catholic countries in the EU now also have substantial proportions of nonmarital births, as of 2016 (except where otherwise stated): Portugal (52.8% ), Spain (45.9%), Austria (41.7%), Luxembourg (40.7%) Slovakia (40.2%), Ireland (36.5%), Malta (31.8%).
To a certain degree, religion (the religiosity of the population - see Religion in Europe) correlates with the proportion of nonmarital births (e.g., Greece, Cyprus, Croatia have a low percentage of births outside marriage), but this is not always the case: Portugal (52.8% in 2016) is among the most religious countries in Europe.