Is It Bad To Have Sex With Your Cousin?

Marrying your cousin might sound icky, but it’s perfectly legal in many countries, including Australia and New Zealand. According to a new large-scale study, the risk of siring offspring with birth defects is actually relatively small; around the same as all expectant mothers over 34.

Six finger picture from Shutterstock

In the largest study of its kind, researchers in the UK analysed data collected from almost 14,000 babies born in Bradford, England between 2007 and 2011 and compared the number of congenital anomalies from both consanguineous (blood-related) and non-consanguineous relationships.

The report found that cousin marriages pose an increase in the risk of birth defects. However, the researchers also noted that the absolute risk of birth defects still remained low.

“This study confirms what has previously been known, that babies born to couples that are related, definitely leads to increased rates of babies born with health problems,” commented Professor Andrew Shelling, Faculty of Medical and Health Sciences at the University of Auckland.

“[However] the increased rate of problems is relatively small, and in cousins, it is not much different to those babies born to unrelated individuals. In an interesting twist, this study shows that the risk is about the same as older women (defined as having babies over 34) having babies.”

Professor Hamish Spencer, Director of the Allan Wilson Centre for Molecular Ecology and Evolution at the University of Otago also released a statement defending consanguineous marriage:

The risk of birth defects in children whose parents are first cousins is often exaggerated in the public’s mind. Most such babies will be fine. All the same, there is an increased occurrence of birth defects in such babies…I would say that this increase can sound large (“twice the risk”) or small (“an increase of only about 3%”) depending on your viewpoint.

In other words, if your cousin is hot, perhaps the risk is worthwhile.

Risk factors for congenital anomaly in a multiethnic birth cohort: an analysis of the Born in Bradford study [The Lancet]

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