A new study has found that children born to parents who are first cousins are more than twice as likely to suffer from birth defects.
A UK based study has drawn data collected from almost 14,000 babies born between 2007 and 2011 and their families.
The Born in Bradford study collected lifestyle and clinical data from children born with birth defects from both blood-related and non-blood related relationships, and took into account factors such as maternal age and socio-economic status.
Researchers found cousin marriages and maternal age were associated with a significant increase in risk of birth defects.
The Bradford study was unusual in that a large number of the children were born into Pakistani families, which traditionally encourage marriage between cousins.
Accounting for other factors such as maternal age and socio-economic status, the authors calculated that 31% of all defects in children of Pakistani origin could be linked to marriage to a cousin.
The authors also mentioned that while there was an increased risk, the absolute risk of birth defects remained low.
The study recommended "clear and accessible information about the risks of consanguineous unions and congenital anomaly should be communicated to couples concerned and widely disseminated to local communities."
However it emphasised that the findings from the study should be presented in a culturally sensitive way.
While counsin marriages are banned in parts of Asia and many US states, marriage of first cousins is legal in New Zealand.
"For some ethnicities, cousin marriage is relatively common, and we have seen increasing numbers of these communities living in New Zealand who will have a long standing tradition of consanguinity," said Associate Professor Andrew Shelling, Faculty of Medical and Health Sciences from the University of Auckland.
"While these increased risks should be clearly communicated to all couples, just as we discuss other potential medical issues for parents, this will need to be done carefully and with cultural sensitively."