"While religiously unaffiliated people now make up 16 percent of the global population, only an estimated 10 percent of the world's newborns between 2010 and 2015 were born to religiously unaffiliated mothers", researchers noted.
Pew adds that "Muslims are projected to be the world's fastest-growing major religious group in the decades ahead...and signs of this rapid growth already are visible". Reports state that in the same period, around 33 percent of the world's babies were born to Christian mothers, the figure is only slightly more than their 31 percent share of the global population, the Guardian reported.
That turnaround will be driven in part by the fact that the Christian population in some parts of the world, such as Europe, is relatively old, with deaths expected to outnumber births in the years to come. By the 2055 to 2060 period, this gap in number of births could reach 6 million (232 million births for Muslims, 226 million for Christians), Pew Research Center reported on Wednesday.
The study also found that while Muslim and Christian populations are expected to grow, those of other major religions - as well as those who are religiously unaffiliated - will shrink.
"In contrast with [the] baby boom among Muslims, people who do not identify with any religion are experiencing a much different trend", said Pew. It draws on more than 2,500 population registers from around the world, as well as the expertise of dozens of religious scholars.
Muslims gave birth to 213 million children and lost 61 million people to death - a net increase of 152 million. Adherents of folk religions, Jews and members of other religions make up smaller proportions of the world's people. For example, 62 percent of USA adults predict that religious "nones" will increase as a share of the world's population in the next few decades.
By 2075, this could result in the number of practising Muslims outweighing Christians for the first time, according to the research, which analysed global birth rates from 2010 to 2060.
While the global population will shift, there will be greater adjustments for a number of regions.
Beyond 2015, Christian and Muslim mothers are expected to give birth to increasing numbers of babies through 2060.
As well as fertility rates, the average ages of those in each religious group will also play a part.
By 2050, almost a quarter of Europeans (23 per cent) are expected to have no religious affiliation, and Muslims will make up about 10 per cent of the region's population, up from 5.9 per cent in 2010.
From 2015 until 2060, Pew expects Christians to increase from 31 percent of the world's population to just 32 percent.