The study also found that people who were unaware that they were conceived using a donor have discovered the truth through finding unexpected family links on ancestry sites.
Professor R贸is铆n Ryan-Flood, of the 糖心Vlog, spoke to 22 donors, recipient parents and children finding that while the revelations could be surprising, they can also lead to positive new relationships.
Professor Ryan-Flood looked at how people who donated before 2005 could expect lifelong anonymity if they chose this, as their donor conceived children were able to see general information about them but not their identity.
But when these donor conceived children took DNA tests through ancestry sites, these revealed unexpected links to the donors鈥 relatives, who had also taken and uploaded tests. By using these results, and further research on social media, the donor鈥檚 identity could be revealed.
Professor Ryan-Flood told the in Manchester that 鈥渋ncreasingly donor conceived people are accessing information about their biological roots, either through genetic testing or social media sites.
鈥淐ontemporary technologies challenge the privacy traditionally associated with donation by providing donor conceived people with the possibility of identifying donors. Anonymity can no longer be guaranteed for donors.鈥
In her study all the donors except one had been traced by DNA testing, Professor Ryan-Flood said. All of the children conceived via a donor traced their donors via DNA testing and in some cases a mixture of DNA tests and social media.
She said: "As DNA testing became more popular, so the numbers of donors revealed was likely to increase."
One donor his sixties told Professor Ryan-Flood that he was traced by his donor-conceived daughter because of DNA profiles on websites which linked her and his relatives.
鈥淢y wife knew that I鈥檇 been a sperm donor. Her first thought was, 鈥榳hat happened to anonymity?鈥. That wasn鈥檛 my first thought. In my head I accepted that the technology had moved on and the agreement to anonymity had become redundant really, because time had got ahead of that.鈥
He established a relationship with his daughter. 鈥淲e quickly sort of struck up a regular correspondence and agreed to meet. This was nearly five years ago, and it was the start of a very positive relationship.鈥
One man found out he had been conceived using a sperm donor when he was told by the parents that if he took a DNA test this would reveal what they had kept from him until then.
鈥淚t was a monumental shock,鈥 he said. 鈥淚 can divide my life up into all the time up until that moment and then all the time since then. The past four years have been this extraordinary journey of me trying to rebuild a sense of identity.
鈥淚 didn鈥檛 know who half of me was at that point. You have such a sense of how nature and nurture works from who your mum and dad are. And suddenly, none of that. I was missing half of the equation.鈥
He spent time on the web to try and trace his donor parent. 鈥淭he internet is full of these anonymous people who are kind of going through all your details and looking for my biological father turned me into one of those people a bit. And I kind of resent it. I resent feeling like I have to become this voyeuristic person prying into other people鈥檚 information, other people鈥檚 lives.鈥
Another man in his sixties told Professor Ryan-Flood that he was contacted by a 19-year-old man who DNA testing revealed as his half-nephew because the young man鈥檚 mother had been donor conceived.
鈥淗e was a 19-year-old kid from the Middle East. And it was just so weird. I thought, 鈥榟ow can that possibly be right?鈥 He messaged me and said, 鈥楬ey, you know, how is it possible that we鈥檙e related?鈥欌
Some of these new connections turned into positive relationships, including between donor conceived siblings.
While donors from April 2005 onwards were informed that their identities would be revealed legally to children when they reached the age of 18 if the children requested this, the anonymity of those donating before 2005 are not required to be divulged officially.