Ties van der Meer doesn’t know how many siblings he has. The 47-year-old was conceived in the Netherlands at a private fertility clinic using sperm from an anonymous donor, and after the Netherlands banned anonymous donation in 2004, the doctor who ran the clinic destroyed records that might have identified those donors, van der Meer says. He describes the situation as “problematic,” arguing that children have a right to know their biological parents, not to be left guessing indefinitely.

Van der Meer did ultimately track down one sibling, which helped him identify his father along with other genetic relatives. But he may have others he’ll never find. That uncertainty is not rare in a world where donor-conceived people can use consumer genetic tests and registries to connect. The article notes that other donor-conceived people who tracked down siblings have found tens or even hundreds of them, including one donor-conceived woman who found 25 half-siblings over seven years and told the Guardian, “It does make you feel a bit mass-produced.” Against that backdrop, a European fertility organization is arguing for international limits on how many children a single donor can contribute to.

The push is aimed at the core policy problem: anonymity is harder to guarantee than regulators and clinics often assume. Today, many countries, including the UK, have banned anonymous egg and sperm donation, but even where anonymity is technically allowed, the downstream tools for DNA matching have changed the game. Genetic tests offered by companies like Ancestry and 23andMe, plus genetic registries, can make it much easier for donor-conceived people to find parents and siblings who share their genes. And because sperm can be frozen and stored for years before it is used, the current setup can create delays where the identity of a genetic parent is discovered only after the person’s death. The result can be siblings of very different ages, sometimes across multiple countries.

Some prolific donors make the math look especially ugly. The article highlights sperm from Jonathan Meijer, a Dutch man who began donating in 2007 and whose sperm was used to conceive between 550 and 600 children. Stichting Donorkind, a foundation and advocacy group chaired by van der Meer, took him to court, and he was ordered to stop donating in 2023. While that case is a spotlight, it is also a warning sign for how one individual’s contribution can multiply through storage, distribution, and cross-border use.

The case for limits is also about safety, not just family knowledge. The offspring of a prolific donor might unknowingly form romantic or sexual relationships, because genetic relatives can be spread widely enough to evade social discovery. And some people worry about donors with harmful genetic mutations passing them on to many children. The article adds that this is unlikely given screening most donors undergo, but it has happened: a man who donated sperm to a sperm bank in Denmark was found to have a genetic mutation that significantly increased the risk of multiple cancers, and his sperm had already been used to conceive at least 197 children across Europe, with some developing cancer and some dying.

Regulatory limits exist in many places already, but they do not naturally solve the cross-border nature of supply chains. In Malta and Cyprus, for example, egg and sperm donors are allowed to contribute to the birth of just a single child, according to data presented at the European Society of Human Reproduction and Embryology (ESHRE) meeting in London on July 8. Other countries set limits based on the number of families a donor can contribute to, allowing recipients to have children who share a genetic link. In the UK, the limit is 10 families per donor. In Denmark, the national limit is 12 families. The enforcement problem is that donated gametes don’t necessarily stay in their original country: in the UK, more than half of sperm donations in 2020 were imported, with most coming from Denmark or the US. Denmark is also a major exporter, which makes local limits less effective when supply can move.

That is why ESHRE is pushing a transnational approach. “The only thing that really makes sense is a transnational limit,” Jackson Kirkman-Brown, a professor of reproductive biology at the University of Birmingham, said at the meeting. Kirkman-Brown and colleagues spent months putting together a document representing ESHRE’s position on these limits. After consulting fertility specialists, clinics, sperm and egg banks, donors, and donor-conceived people, they developed a plan to start with a Europe-wide limit on sperm and egg donations. ESHRE is calling on sperm and egg banks and fertility clinics to respect an initial limit of 50 families per donor. That’s still very high, according to a handful of people the article says it spoke to at the meeting. Europe should move toward setting limits at 15 families per donor, Kirkman-Brown said.

Several experts and stakeholders also underline that “hard-to-enforce” is not the same as “optional.” If strict limits reduce the supply of donor sperm, some people might turn to unregulated sperm donations from people who do not undergo health screening, the article notes. Unregulated donations can bring other problems, including the possibility that donors seek parental rights over children conceived using their sperm. It would also become harder to establish international limits if supply shifts to less regulated channels.

The Atlantic crossing matters too, at least as a reference point. When the American Society of Reproductive Medicine was asked about ESHRE’s proposed limits, a representative directed to a guidance document suggesting that for a population of 800,000, single donors should be limited to “no more than 25 births” to avoid relatives having children together. The article adds that with the US population of over 340 million, the total figure could be pretty high, but many sperm banks opt to limit families contributed to around 25. Van der Meer thinks even five families would be too high for a single donor, and he argues that international contributions should be set at two families because international donation makes it harder for donor-conceived people to connect with genetic relatives. Still, he calls ESHRE’s suggested limit a “positive first step,” concluding that “you have to start somewhere.”

For executives and board-level leaders in fertility services, the strategic stake is straightforward: these limits will not stay theoretical. They will pressure how clinics source inventory, how banks structure donor rosters, how compliance programs measure international distribution, and how risk is allocated when anonymity, testing, and cross-border supply collide. In a market where DNA tools can reveal relationships years later, policies around donor limits are becoming product decisions as much as they are ethics decisions. The question is not whether regulation will move, but how quickly systems that were built for national rules will adapt to transnational limits that treat knowledge, safety, and enforcement capacity as a single problem.