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.

Earlier attempts to investigate the cases were blocked by Karbaat’s widow, who refused to allow the use of his DNA profile.

After Karabaat’s death dozens of people came forward to say they suspected that he had used his own sperm to impregnate their mothers.

A group of donor children and their parents took legal action to find out the truth in 2017. Some plaintiffs bore obvious physical resemblances with the doctor but appeared markedly different from their supposed sperm donors, the court was told. 

Judges ruled that materials containing Karbaat’s DNA could be collected from his home after his death, but said his DNA profile had to remain sealed pending the outcome of further court cases.

The controversial case attracted enormous public attention when a group of suspected “Karbaat children” took his relatives to court to force them to release the profile, which was locked in a safe.

The Rotterdam District Court overruled his widow’s objections in February and ordered the profile to be made available to parents and children who wished to compare their own DNA with the doctor’s.  

One of the doctor’s biological children, Eric Lever, told the NRC newspaper that he felt no anger towards Karbaat.

“I don’t get the feeling that he cheated my mother,” Mr Lever said. “She really wanted a child and could not have one with my parental father.”

Another of the children, named as Joey, said the knowledge that Karbaat was his biological father had given him closure. “After a search of 11 years I can continue my life,” he said.

Tim Bueters, a lawyer who represented the 49 people involved, said he was pleased that they now knew the truth. “It means that there is finally clarity for the children who are matched,” he said.

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Iara de Witte, a Defence for Children advisor, said: “The judge placed the interests of the child above the right to privacy of Mr Karbaat and his family. This is a great asset, after years of uncertainty, the plaintiffs can finally close a chapter and they can start processing the fact that they are one of Karbaat’s many descendants.”