A British man may have fathered 600 children by repeatedly using his own sperm in a fertility clinic he ran, it has emerged.
Bertold Wiesner and his wife Mary Barton founded a fertility clinic in London in the 1940s and helped women conceive 1,500 babies.
It was thought that the clinic used a small number of highly intelligent friends as sperm donors but it has now emerged that around 600 of the babies were conceived using sperm from Mr Wiesner himself.
Two men conceived at the clinic, Barry Stevens a film-maker from Canada and David Gollancz, a barrister in London, have researched the centre and DNA tests suggest Mr Wiesner, an Austrian biologist, provided two thirds of the donated sperm.
Such a practice is outlawed now but at the time it was not known that Mr Wiesner was providing the majority of the samples.
The same sperm donor should not be used to create so many children because of the risk that two of the offpsring will unwittingly meet and start a family of their own, which could cause serious genetic problems in their children.
DNA tests were conducted on 18 people conceived at the clinic between 1943 and 1962. The results showed that two thirds of them were fathered by Mr Wiesner.
Extrapolating this to the rest of the children conceived at the clinic it would suggest around 600 of the children were Mr Wiesner’s.
Mr Gollancz told the Sunday Times: “A conservative estimate is that he would have been making 20 donations a year.
“Using standard figures for the number of live births which result, including allowances for twins and miscarriages, I estimate that he is responsible for between 300 and 600 children.”
Allan Pacey, chairman of the British Fertility Society and expert in male fertility, said a healthy man could make that many donations a year if it were legal.
In 1990 the Human Fertilisation and Embryology Act set up a regulator of fertility clinics and limits were set on the number of families a sperm or egg donor could provide.
Sperm donors can provide samples for the creation of up to ten families.
The limit is set as families, rather than the number of children, so parents can choose the same donor for a second or third sibling without being told that donor has reached his limit.
Around 2,000 children are born every year in Britain using donated eggs, sperm or embryos.
All sperm donors used by regulated clinics should be between the age of 18 and 41 and all samples are tested for diseases.
Information about the donor is kept so the children can apply to find out the identity of their biological father and any half brothers or sisters once they turn 18.