Ties van der Meer doesn’t know how many siblings he has. He was conceived at a private fertility clinic in the Netherlands using sperm provided by an anonymous donor, and he says that after the Netherlands banned anonymous donation in 2004, the doctor who ran the clinic destroyed records that might have identified those donors. He calls the situation “problematic,” and says children have a right to know their biological parents. Even though he was able to track down one sibling, who helped him identify his father along with other genetic relatives, he may still have others he’ll never find.

That personal uncertainty is exactly what is driving a broader policy push in Europe right now. At a conference in London, members of a European fertility organization laid out plans to start with a Europe-wide limit on the number of children a single donor can contribute. Today many countries, including the UK, have banned anonymous egg and sperm donation, but the article makes a key point: anonymity cannot be guaranteed even where it is technically allowed because genetic testing has changed the game. Companies like Ancestry and 23andMe, plus genetic registries, make it much easier for donor-conceived people to find genetic relatives who share DNA. And because sperm can be frozen and stored for years before it is used, some donor-conceived people may only learn their genetic parent’s identity after that parent has died. They can also find siblings born at very different times, across the world.

The “how many siblings?” problem is not hypothetical. Other donor-conceived people who tracked down siblings have reported finding tens or even hundreds of them. One donor-conceived woman who found 25 half-siblings over the course of seven years told The Guardian, “It does make you feel a bit mass-produced.” That framing matters for policymakers because it’s not just about information rights. It’s about downstream harms that start quietly and scale silently.

One of the most cited risks is accidental family entanglement. The offspring of a prolific donor might unknowingly form romantic or sexual relationships. Another risk is inherited genetic disease: a donor with a harmful genetic mutation could pass that down to many children. Screening makes that unlikely “given the level of screening that most donors undergo,” the article notes, but it isn’t impossible. It points to a case where 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. His sperm had already been used to conceive at least 197 children across Europe, and some developed cancer while some died.

So where does Europe land on limits today? The article says many countries already have legal caps, but the specifics vary. In Malta and Cyprus, both egg and sperm donors are allowed to contribute to the birth of just a single child, according to data presented at the ESHRE meeting in London on July 8. Other countries set limits based on the number of families a donor can create, so recipients can have children who share a genetic link. In the UK, the limit is set at 10 families per donor. In Denmark, the national limit is set at 12 families. The catch is enforceability and the fact that sperm does not respect borders.

That cross-border reality is the main reason ESHRE is pushing a transnational solution. The article notes that it is difficult to enforce because donated gametes don’t necessarily stay in their original country. Denmark is a major exporter of sperm, and in the UK, for example, more than half of sperm donations in 2020 were imported, with most coming from either Denmark or the US. “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 that represents ESHRE’s position on these limits. After consulting fertility specialists, clinics, sperm and egg banks, donors, and donor-conceived people, the team’s plan is 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. The article adds that 50 is still very high, according to a handful of people I spoke to at the meeting, and ESHRE is not claiming it is the final number. Europe should move toward setting limits at 15 families per donor, Kirkman-Brown said. Vasanti Jadva, who studies the psychological well-being of people conceived using donated eggs, sperm, and embryos at City St George’s in London, said, “We may find that 15 is also too high.” She adds that, “We still don’t know what the right number is.”

Even if Europe agrees on a number, the next problem is supply and the black market. The article warns that if tighter limits reduce the availability of donor sperm, some people may turn to unregulated sperm donations from people who do not undergo health screening. Unregulated donations create other problems for prospective parents, including the possibility that donors will seek parental rights over the children conceived using their sperm. And it will be even harder to set international limits if countries move at different speeds.

The article also contrasts ESHRE’s Europe-facing approach with the American framework that was referenced by the American Society of Reproductive Medicine. When the MIT Technology Review team asked for its thoughts, a representative directed the publication to a guidance document saying “it has been suggested” that for a population of 800,000, single donors should be limited to “no more than 25 births” to avoid the risk that relatives will have children together. It notes that, considering the US population is over 340 million, the total figure could be pretty high. It also points out that many sperm banks opt to limit the number of families contributed by a single donor at around 25.

Where does van der Meer fit into this policy calculus? His view is more aggressive than the proposed ESHRE starting point. He thinks even a limit of five families from a single donor would be high, and says that international contributions should be capped 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.” After years of searching, he has managed to track down a sibling, his father, and nephews, aunts, and uncles. He hopes future policies respect the rights of donor-conceived children to know and be in contact with their genetic relatives. “But,” he says, “you have to start somewhere.”

For executives and boards in the fertility ecosystem, the strategic stake is straightforward: this is moving from case-by-case enforcement and national rules toward a system-level coordination problem. If donor supply gets squeezed, the industry will have to prove it can maintain screening quality and avoid creating perverse incentives toward unregulated sourcing or legal disputes. If adoption of limits is inconsistent across countries, cross-border logistics will keep undermining those limits. Either way, the next regulation wave is likely to hit operators that are currently set up for a patchwork world, and it will demand new governance, reporting, and compliance infrastructure fast.