London: The chances of having a baby with potentially life-threatening birth defects doubles in case of 'first cousin marriages', a study has revealed.

From a sample of nearly 11,000 births between 2007 and 2011, more than 2,000 babies were born to first cousin parents- predominately from the city's large Pakistani population, a website reported.

Researchers from the University of Bradford and the University of Leeds found that the children of such unions had a six percent chance of having a congenital abnormality, compared to an average 3 percent chance.

The new "Born in Bradford" study suggested that kids born to parents who were not cousins but were closely related also had an increased risk.