A Dutch fertility doctor secretly fathered at least 49 children by inseminating female patients with his own sperm, telling the women that it came from anonymous donors.

DNA tests have confirmed suspicions that Jan Karbaat, who died in 2017 aged 89, used his own semen without his patients’ consent.

The tests, carried out by a hospital in the south-eastern Dutch city of Nijmegen, have now proved that “49 children in this case are direct descendants of the late Karbaat,” the Defence for Children organisation said. “The results confirm serious suspicions that Karbaat used his own sperm at his clinic.” The non-governmental organisation represents parents and children born after treatment at his clinic in the Rotterdam suburb of Barendrecht.

The clinic was closed in 2009 amid allegations that Karbaat had falsified data, analyses and donor descriptions and exceeded the permitted number of six children per donor.

Karbaat, who described himself as a “pioneer in the field of fertilisation”, admitted before his death that he had used his own sperm to father about 60 children.

He said he had sometimes mixed his sperm with that of other donors. Defence for Children said his semen “was also distributed to other clinics”. Most of the children were born in the 1980s.