Why do sperm donors have hundreds of children?

The rules vary around the world, but in the UK you also need to be relatively young – between 18 and 45; not have infections such as HIV and gonorrhea and not carry mutations that can cause genetic diseases such as cystic fibrosis, spinal muscular atrophy and sickle cell anemia.

Overall, this means that the number of people who end up becoming sperm donors is low. In the UK, half of sperm ends up being imported.

But biology means that a small number of donors can produce a large number of children. One sperm is enough to fertilize an egg, but there are tens of millions of sperm in each ejaculation.

Men come to the clinic once or twice a week during their donation, which can last for months.

Sarah Norcross, director of the Progress Educational Trust charity, which works on fertility and genomics, said the shortage of donor sperm has made it “a precious commodity” and “sperm banks and fertility clinics are maximizing the use of available donor sperm to meet demand”.

Among this small group of donors, some men’s sperm is simply more popular than others.

Donors are not chosen at random. It’s a process similar to the cruel reality of dating apps, where some men receive many more matches than others.

Depending on the sperm bank, you can see photos, hear their voice, find out what their profession is: engineer or artist? – and check height, weight and other information.

“If their name is Sven, they have blonde hair, they’re six feet tall, they’re an athlete, they play the violin and they speak seven languages, you know they’re way more attractive than a donor who looks like me,” says male fertility specialist Allan Pacey, pictured, who ran a sperm bank in Sheffield.

“Ultimately, people swipe left and right when it comes to finding a donor match.”

Denmark is home to some of the largest sperm banks in the world and has become famous for producing “Viking babies.”

Ole Schou, 71, founder of sperm bank Cryos International, where a single 0.5ml vial of sperm costs between €100 (£88) and more than €1,000 (£880), says the culture around sperm donation in Denmark is very different from that in other countries.

“The population is like a big family,” he says, “there are fewer taboos around these issues, and we are an altruistic population, many sperm donors also give blood.”

And this, according to Schou, has allowed the country to become “one of the few exporters of sperm”.

But he says Danish sperm is also popular because of genetics. He told the BBC that the “Danish blue-eyed, blond-haired genes” are recessive traits, meaning they must come from both parents to appear in a child.

As a result, the mother’s characteristics, such as dark hair, “may be dominant in the resulting child,” says Schou.

He says the demand for donor sperm comes primarily from “single, highly educated women in their 30s.” They currently represent 60% of requests.

One aspect of the sperm donor investigation published earlier this week concerned how a man’s sperm was collected at the European Sperm Bank in Denmark and then sent to 67 fertility clinics in 14 countries.

Countries have their own rules regarding the number of times a man’s sperm can be used. Sometimes this is related to the total number of children, other times it is limited to a certain number of mothers (so each family can have as many related children as they want).

The initial argument around these limits was to prevent half-siblings – who didn’t know they were related – from meeting, forming relationships and having children.

But nothing prevents sperm from the same donor from being used in Italy and Spain then in the Netherlands and Belgium, provided that the rules of each country are respected.

This creates circumstances in which a sperm donor can legally father a large number of children. Although man often ignores it.

“Many recipients, like donors, are unaware that sperm from a single donor can be used legally in many different countries. This fact needs to be better explained,” says Sarah Norcross, who says it would be “reasonable” to reduce the number of children a donor can have.

In response to the investigation into the sperm donor who passed on a gene that caused cancer in some of the 197 children he fathered, Belgian authorities have asked the European Commission to create a European sperm donor registry to monitor the cross-border transport of sperm.

Deputy Prime Minister Frank Vandenbroucke said the sector resembled the “Wild West” and “the original mission of offering people the opportunity to start a family has given way to a real fertility business.”

The European Society of Human Reproduction and Embryology has also proposed a limit of 50 families per donor across the EU. This system would still allow one donor’s sperm to generate more than 100 children, if families wanted to have two or more babies each.

Concerns have been raised about the impact on children conceived through sperm donation. Some will be happy, others may be deeply upset by the double discovery that they were conceived with donor sperm and that they are one of a hundred half-siblings.

The same goes for donors, who are often unaware that their sperm is being distributed on such a scale.

These risks are amplified by readily available DNA ancestry tests and social media, where people can search for their children, siblings, or the donor. In the UK, there is no longer anonymity for sperm donors and there is a formal procedure by which children can find out the identity of their biological father.

Schou of Cryos says new restrictions on sperm donation would only cause families to “turn to the completely deregulated private market.”

John Appleby, a medical ethicist at Lancaster University, said the implications of such widespread use of sperm constitute a “vast” ethical minefield.

He said there are issues around identity, privacy, consent, dignity and more, making it a “balancing exercise” between competing needs.

Appleby said the fertility industry had a “responsibility to control the number of times a donor is used”, but acknowledged it would undeniably be “very difficult” to reach agreement on global regulation.

He added that a global sperm donor registry, which has been suggested, carries its own “ethical and legal challenges”.