At least 85 sperm donors in the Netherlands have fathered 25 or more children, the national gynaecology and obstetrics organisation has said, after a new registration system showed fertility clinics have been breaking existing rules on sperm donation for decades.

The NVOG said on Monday that some clinics had deliberately used sperm batches more than 25 times, exchanged sperm without the necessary paperwork or donors’ knowledge, and allowed the same donors to donate sperm at multiple clinics.

“The number of so-called ‘mass donors’ should be zero,” gynaecologist Marieke Schoonenberg told the TV show Nieuwsuur. “On behalf of the whole profession, we wish to apologise. We didn’t do things as they should have been done.”