A fifth fertility doctor who has been found to have used his own sperm to father children says the discovery came ‘as a total surprise’, the Volkskrant reported on Friday.

The man, Henk Ruis (71), agreed to cooperate with a dna investigation following the discovery by one donor child that he was his biological father, according to donor children association Stichting FION. The organisation then decided to publish the doctor’s name in case more cases would come to light.

Ruis fathered at least three children at the end of the 1980s and the beginning of the 1990s. In one case the agreement was not to use donor sperm but the the sperm of the woman’s husband.

Ruis claims his sperm must have been mixed or exchanged with donor sperm pointing to ‘the primitive lab facilities’ at the time. The fact that his sperm was present in the clinic at all had to do with the testing of freezing equipment, he said.

The Nij Geertgen clinic in Noord-Brabant where the man worked said it would have been unacceptable if he had donated his own sperm, even if the rules at the time meant men could do so anonymously.

‘There were no rules for donor conception but then, as now, it was considered unethical for a doctor to use his own sperm whithout consulting the parents and asking their permission,’ a spokesperson fort he clinic told the paper.

The case brings the number of fertility doctors who used their own sperm without the permission of the mothers to five.

More donor children are asking for information to find out who their biological father is, partly prompted by the news about the doctors.

Before June 2004  sperm donors had the option to remain anonymous but from that date all data surrounding artificial insemination must be registered and made available on request, including anything on record from before 2004.