Why do sperm donors have hundreds of children?

Some men are having a large number of children through sperm donation. This week the BBC reported on a man whose sperm contained a genetic mutation that dramatically increases the risk of cancer for some of his offspring.

One of the most striking aspects of the research was that the man’s sperm was sent to 14 countries and produced at least 197 children. The revelation was a rare insight into the scale of the sperm donor industry.

Sperm donation allows women to become mothers when it would not otherwise be possible: if their partner is infertile, they are in a same-sex relationship or they are single mothers.

Meeting that need has become big business. The market in Europe is estimated to be worth more than £2 billion by 2033, with Denmark a major exporter of sperm.

So why do some sperm donors father so many children, what made the Dane or the so-called “Viking sperm” so popular? Is it necessary to control this industry?

If you’re a man reading this, we’re sorry to tell you, but your sperm quality probably isn’t good enough to become a donor: fewer than five in 100 volunteers make the grade.

First, you have to produce enough sperm in a sample; that’s you sperm count – then pass checks on how well they swim – their motility – and in its form or morphology.

Sperm is also monitored to ensure it can survive freezing and storage in a sperm bank.

You could be perfectly fertile, have six children, and still be unfit.

The rules vary around the world, but in the UK you also have to be relatively young: between 18 and 45; be free of 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.

Generally, it means that the pool of people who ultimately become sperm donors is small. In the UK, half of sperm ends up being imported.

But biology means that a small number of donors can father a large number of children. Only one sperm is needed to fertilize an egg, but each ejaculation contains tens of millions of sperm.

Men will come to the clinic once or twice a week while they donate, which can last for months.

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

Of this small group of donors, some men’s sperm are more popular than others.

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

Depending on the sperm bank, you can search for photos, listen to their voice, find out what job they do: engineer or artist? – and check your height, weight and more.

“You know, if their name is Sven and they have blonde hair, are 6ft 4 (1.93m) and are athletes, play the violin and speak seven languages, you know that’s a lot more attractive than a donor who looks like me,” says male fertility expert Professor Allan Pacey, pictured, who used to run a sperm bank in Sheffield.

“Ultimately, people lean left and right when it comes to donor compatibility.”

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

Ole Schou, 71, founder of the Cryos International sperm bank, 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 to other countries.

“The population is like a big family,” he says, “there is less taboo about these topics and we are an altruistic population, many sperm donors also donate blood.”

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

But he maintains that Danish sperm is also popular because of genetics. He told the BBC that the “Danish genes for blue eyes and blonde hair” are recessive traits, meaning they must come from both parents to appear in a child.

As a result, the mother’s traits, such as dark hair, “could be dominant in the resulting child,” Schou explains.

He says demand for donor sperm comes primarily from “single, highly educated women in their 30s who have focused on their careers and abandoned family planning too late.” They currently represent 60% of applications.

One aspect of the sperm donor research published earlier this week was 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 about how many times a man’s sperm can be used. Sometimes it is linked to a 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 original argument around those boundaries was to prevent half-siblings, who didn’t know they were related, from meeting each other, forming relationships, and having children.

But nothing prevents sperm from the same donor from being used in Italy and Spain and then in the Netherlands and Belgium, as long as the rules in each country are followed.

This creates circumstances in which a sperm donor can legally father a large number of children. Although man often does not know that fact.

“Many recipients, and also donors, do not know that sperm from a single donor can be used legally in many different countries; this fact should be better explained,” says Sarah Norcross, who maintains that it would be “sensible” 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, officials in Belgium have called on the European Commission to establish a Europe-wide sperm donor registry to monitor sperm traveling across borders.

Deputy Prime Minister Frank Vandenbroucke said the industry was like the “wild west” and that “the initial mission of offering people the chance 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. That system would still allow one donor’s sperm to produce more than 100 children if families wanted two or more babies each.

Concerns have been raised about the impact on children conceived through sperm donation. Some will be happy, others may feel deeply distressed by the double discovery of having been made with donor sperm and being one of hundreds of half-siblings.

The same goes for donors, who often have no idea that their sperm is distributed so widely.

These risks are amplified by readily available DNA ancestry tests and social networks 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 an official process by which children learn the identity of their biological father.

Cryos’ Schou argues that more restrictions on sperm donation would only lead families to “turn to the totally unregulated private market.”

Dr John Appleby, a medical ethicist at Lancaster University, said the implications of using sperm so widely were a “vast” ethical minefield.

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

Dr Appleby said the fertility industry had a “responsibility to control the number of times a donor is used” but agreeing global regulations would clearly be “very difficult”.

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