A Dutch fertility doctor, Jan Karbaat, has fathered 49 children by tricking couples who visited his Rotterdam clinic into believing they had chosen other sperm donors for insemination while in fact he used his own sperm, an NGO revealed.

"The results of DNA tests confirm serious suspicions that Karbaat used his own sperm at his clinic," Defense for Children affirmed.

Before his death in 2017, the 89-year old doctor had confessed to having fathered about 60 children in his time at the discredited clinic which closed in 2009 amid reports of irregularities and to mixing sperm from various donors and issuing fraudulent donor documentation, the Dutch daily newspaper NRC reported.

The Karbaat family's lawyers argued that their clients' right to privacy must be respected.

"However, with the judges agreeing to the paternity test, the judge placed the children's rights above those of Karbaat and his family. Now, after years of uncertainty the plaintiffs can finally close a chapter and start processing the fact that they are one of Karbaat's many descendants," Defense for Children advisor Iara de Witte said.

"Sperm belonging to the late doctor was also distributed to other clinics," Dutch news agency ANP quoted the organization as saying, highlighting the possibility of him having fathered even more children.