Sydney: Hundreds of young Australians who were conceived with donor sperm but never told of their genetic heritage may soon receive a letter breaking the bombshell news of their conception.

An unparalleled and highly contentious legal provision makes the state of Victoria, in southern Australia, the only place in the world where donors of sperm or eggs used in IVF have the right to seek out their biological offspring.

This month, a group of donor-conceived teenagers will become the first to reach adulthood since the state parliament passed the Infertility Act in 1988.

The legislation allows for such children, on reaching 18, to seek contact with the strangers who helped create them. But, in a twist that has caused uproar among infertility experts, it also contains a clause giving donors the same right.

While their offspring have the right to refuse contact, they must still be informed that a request has been made.

Thus, one way or the other, the circumstances of their conception will have to be revealed.

Research shows that as few as 30 per cent of affected children have been told the truth of their biological origins, and doctors are appalled at the predicament that awaits unsuspecting teenagers.

Prof Gab Kovacs, medical director of Australia's largest fertility operation, Monash IVF, said the legislation created an ethical minefield that had the potential to damage hundreds of families.

He recently surveyed more than 100 patients who had used donors and discovered that only one in three had told their children the whole story.

"Even though young people have the option of refusing to meet their donors, the secret of their conception, and it is a secret in two out of three cases, would still have to be released," Kovacs said.

"It's a stupid situation and I think it is going to cause a lot of problems."

Critics believe that the law, while addressing issues of donors' rights, does not have sufficient regard for the long-term consequences.

Yet for many sperm donors and offspring, the legislation marks a step towards greater openness in an area that has long been cloaked in secrecy and shame.

Victoria's Infertility Treatment Authority (ITA), which is managing the legislation, has mounted an extraordinary campaign in recent weeks, urging parents who have conceived with donor sperm or eggs to tell their children the truth.

Louise Johnson, the ITA's chief executive, said: "We are in a unique position... because there isn't another situation anywhere in the world that we could learn from."