But nearly all nations share two salient factors in common: the numbers have skyrocketed in recent decades, and the increase is due to children born to co-habitating couples, not to single mothers.
"Marriage is no longer considered an indispensable preliminary to welcoming a child" found a recent French parliamentary report on the family, which noted that "free unions" have become much more common - and not just for very young people.
In Germany, a recent Federal Statistics Office survey reached similar conclusions: only 38 percent of women and 30 percent of men see marriage as a necessary part of living together.
In Britain, the Office for National Statistics (ONS) found in 1999 that cohabiting couples accounted for 24 percent of the men living in any kind of partnership and 25 percent of women - double the rates prevalent in 1986.
"People these days don't expect their marriages to last, so they think 'why get married in the first place if weddings are expensive and divorce complicated?' " says Dr. Brierley, whose organization provides information to help British church leaders make informed policy decisions.
And where there are cohabiting partnerships, there are babies. "One of the important engines behind the rise in non-marital childbearing," said the ONS study of European trends, "is the rise in cohabitation that has occurred, particularly since the 1980s, in many European countries."
Ermisch, the University of Essex professor, sees the origins of the trend in the contraceptive pill, which began to enjoy wide popularity in Europe in the 1970s. "It used to be very costly to delay marriage," he argues.
"Either you didn't have sex or you risked having an illegitimate baby. The pill made delay less costly," he says, and as live-in couples formed - and firmed up - increasingly they decided to start a family.