Within 20 years, more babies will be born to Muslim women than to Christian women world-wide, the latest sign of the rapid growth that could make Islam the world’s largest religion by the end of the century. Islam is already the world’s fastest-growing religion, according to a new study released Wednesday by the nonpartisan Pew Research Center, with the Muslim population increasing by more than 150 million people between 2010 and 2015, to 1.8 billion. Meanwhile, Christianity remains the world’s largest religion.

It is growing more slowly, however, largely due to its declining numbers in Europe, which was long the seat of Christendom. As of 2015, there were 2.3 billion Christians.While Christians accounted for 33% of births world-wide in recent years—slightly outpacing the number of Muslim births—they also made up 37% of world-wide deaths, nearly twice the share of deaths from any other religion. MORE