The number of children born outside marriage in the United States has increased dramatically to four out of ten of all births.
Figures show that 41 per cent of children born in 2008 did not have married parents - up from 28 per cent in 1990.
Researchers have concluded that although Christian values still play an important role in American society, public attitudes have changed.
Having a child out of wedlock does not carry the stigma and shame it once did, they say.
The study also found that in America there is a declining number of teenage mothers and rising numbers of older parents.
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