The National Infertility and Adoption Education Organization has a Question and Answer about “Accidental Incest between Donor Conceived People.”
Q: How worried should I be about inadvertent partnering of two donor conceived half siblings from the same donor?The main worry is an artificial one... undue criminalization of such relationships.
From their answer...
While the fear is understandable, many professionals believe the fear is not well founded. For example, we asked this question to Ole Schou, founder and CEO of Cryos International sperm banks, who has researched and spoke to professional groups on this issues. [Note that he is not a native English speaker.]I agree.
“There is no reason to be concerned about accidental incest between donor conceived children/adults. The risk is extremely low. Professionals call the risk consanguinity or inbreeding. It is also described as incest. However, this word is surrounded by many taboos and connected to something morally wrong, and is not the best word to use in this situation.
The concern is for the increase in recessive DNA disorders in children where the parents DNA are too closely matched. Remember that all humans have plenty of these recessive genes (C.J. Bell 2011).That is what we’ve been saying.
However, the risk may only be increased some few percentage in comparison to normal procreation. So this is not much. It is more a problem if it continues generation after generation.
This is not relevant for donors as it is only a one generation issue.It might be tempting for someone working for a sperm bank to claim that if a donor-conceived person walks into a room with 100 people in it, one conceived from the same donor, and chooses one person to approach, there is only a 1% chance it will be their half-sibling (if we’re talking egg or sperm donation, full sibling if we’re talking donated embryos). However, there odds are probably going to be much higher because of the shared genes. That is one reason Genetic Sexual Attraction happens. Sharing genes can cause people to be strongly attracted to each other. This is going to happen more and more as more and more people, for reasons including donation as well as many other reasons, are raised apart from close genetic relatives.
Further, the risk that two half siblings from the same donor meet each other is generally very little if the sperm bank distribute internationally or worldwide.
Donors are often screened for genetic problems, so that is a plus for avoiding problems.
Anyway, it is interesting to see what they had to say about risks to children born of consanguineous parents.