Question to cousinfacts tumblr on reproduction facts

rainbowamory asked: Hi. I have a question. While I was looking up information on the statistics for cousin couple reproduction, I came across some conflicting data. Some sources said that cousin couples have a 5% chance of genetic defects occurring in their offspring. Others said 7%. Can you please let me know what the updated facts are? (for non-related couples vs. cousin couples). Thank you 🙂


Hey, rainbowamory! That’s a great question. There is no right or wrong answer, as each study has slightly different findings.  Essentially, it appears to change from 5% to 7% in two different studies based on the definition of the significance of defects.  (i.e. Is a certain disorder considered “significant” or not?) Additionally, it is hard to get cousin couples to agree to participate in some studies because of the stigma surrounding the relationships, so the data is often outdated or flawed.

That said, most studies agree that the increase on risk for cousin couples vs. non-cousin couples is an increase of between 1-3%, which according to the National Society of genetic counselors, while not insignificant, likely does not represent a significant enough risk of harm to warrant protective marriage legislation. Many other groups face similar or greater statistical risks, including Ashkenazi Jews, African Americans, people of Greek descent and women over 35. Almost all cousin couple genetic problems can be avoided with genetic testing, so most people would agree that the best thing to do for cousin couples is to try bring the relationships out into the open so that they aren’t afraid to talk to doctors and additional studies can be done.

Let us know if we can get you any additional information, or answer further questions. We feel that if more people understood and knew about this topic, it would help reduce a lot of problems.

Thank you so much for that detailed answer. It was very helpful, and positive too. 🙂 I only hope more cousin couples participate in future studies to create more data. It would really help reduce the stigma around their relationships in the long term.

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