In 1999 a white American woman gave birth to one white and one black boy after an IVF mix-up.

The fertility clinic in New York where Donna Fasano was treated accidentally implanted her with fertilised embryos belonging to another couple as well as her own.

As a court case loomed Mrs Fasano, then 37, agreed to return the black child to his biological parents.

Both Mrs Fasano and Deborah Perry-Rogers, 34, had tried for years to have children before they visited the fertility clinic in Manhattan and received fertilised eggs on the same day. A month later Mrs Perry-Rogers, who is black, was upset to discover that she was still not pregnant.

But Mrs Fasano was delighted to be told that she was carrying twins. Before the children were born, however, doctors had to break the news that she may have been implanted with up to three embryos belonging to another couple.

DNA tests confirmed she was carrying one child who was not biologically related to her but she went ahead with the pregnancy. Meanwhile, the Rogers learned that Mrs Fasano might be carrying what they considered to be their child and sued for custody.

The twin pregnancy could have produced two black babies, two white babies or - as happened - one of each. For three months after the children's birth, the Fasanos refused to hand over the black child, or even to tell the Rogers if one of the children was black.

But as the court case approached, they decided to hand over the black child after DNA tests confirmed he was the Rogers' biological son.

The Fasanos' lawyer, Ivan Tantleff, said: "The Fasanos have reared, loved and cared for both children as their own. Mrs Fasano doesn't look at them as white and black. She looks at them as her sons. She is torn apart by this. But at the same time she doesn't want to deprive her son of being with his biological mother."

Mrs Fasano said: "We want what's in the interest of the child. We're giving him up because we love him."

A woman in Holland, Wilma Stuart, was also the victim of an IVF mix-up. She also had twins but was suspicious that one of them had much darker skin than herself and the other child. DNA tests later proved a hospital mixed sperm from Mrs Stuart's husband with sperm from a black man.

In 1993 two British women took legal action after having abortions when they discovered that they had been implanted with the wrong embryos.

Two years ago the disappearance of frozen embryos from a clinic in Basingstoke, Hampshire, led to fears that women may have given birth to the "wrong" babies.