A new national registry has revealed at least 85 very prolific sperm donors in the Netherlands so far.

The Artificial Fertilisation Donor Data Act introduced a national registry to systematically track donor sperm use in the Netherlands, assigning unique codes to mothers and donors. The new law came into force in April 2025 and applies retroactively to 2004, when donors' right to anonymity was lifted. Initial data revealed that at least 85 donors exceeded the previous limit of 25 children per donor (reduced to 12 in 2018).

'I deeply regret that these excesses have been discovered,' Vincent Karremans, Minister of Youth, Prevention and Sport, wrote in a letter to the Dutch Parliament, blaming poor oversight and record-keeping by fertility clinics for the scale of mass donation.

Some fertility clinics deliberately reused the same donor or exchanged sperm between clinics without informing donors or recipients. While some donors were active across multiple clinics, others were selected repeatedly by mothers for additional children at clinics which failed to track the cumulative number of offspring. Most mass donors fathered between 26 and 40 children, although some reached as many as 50 to 75.

'The number of the so-called mass donors should have been zero, we want to offer our apologies on behalf of the profession,' Marieke Schoonenberg, gynaecologist and medical director at Nij Geertgen Centre for Fertility, told NOS. 'We didn't do things as they should have been done.'

The mass donors included at least ten fertility doctors and some names that have made headlines in recent years. Among them are Jonathan Jacob Meijer, subject of the Netflix documentary 'The Man with 1000 Kids' (see BioNews 1257) and Dr Jan Karbaat, who fathered at least 49 children through his clinic (see BioNews 996).

The registry data revealed nearly 24,000 instances of donated sperm use for IVF between 2004 and 2018. Donated sperm from mass donors may suggest that children born through donor insemination may have far more half-siblings than previously believed.

Donorkind, a volunteer organisation supporting donor families, described the situation as a 'medical calamity' and estimated that at least 3000 children in the Netherlands now have 25 or more half-siblings. The organisation reported hearing from distraught mothers and overwhelmed donors alike. They called on the government to disclose the exact number of those affected and consider regulating sperm imports.

'For donor children, it's just chaos,' Inge Poorthuis, a Donorkind board member, told the New York Times 'The industry is focused excessively on profit. They're just not careful with creating life.'

Under the new rules, clinics that violate the regulations can now be sanctioned through civil courts, however the new rules do not apply to imported sperm.