Muslims love quoting the fact that 'Islam is the fastest growing religion in the world' and there are 1.6 billion Muslims and growing. The implications are that ... It's great to be on the winning team; Islam must be 'right'; Praise be to God for leading so many people to the 'right' path.What gets overlooked by Muslims are the reasons for this growth - it does not consist of vast numbers of converts from other (or no) religion turning to Islam. Yes there are a few converts, but the numbers are insignificant. Converts are often referred to as 'reverts' because everyone has a 'natural born state' as Muslim (apparently).
The reason for the growth in the numbers of Muslims is that Muslim countries are relatively backward and have appallingly low levels of literacy and education which leads to high birth rates.
The Pew Forum has some enlightening studies of the situation which are worth a read.
The general level of education within a society - and especially girls/women - is a key factor determining the wealth of the nation and the birth rates. Birth control and urbanisation are secondary factors, This link describes the various factors and their relationships very clearly.
The graph above includes a 'best-fit' line though the data points, which shows the relationship between years of schooling and fertility rate - the uneducated girls tend have more children.
It means that vast numbers of these Muslims cannot read, at all, in any language. They have not chosen their religion from a position of knowledge - they've simply been indoctrinated by their family and society. They have been presented with a totally biassed view of the world and prevented from accessing information about alternatives. This is not something to be proud of !