Nine out of ten parents whose children were conceived using donor sperm have not told them the truth about their parents, research reveals.

Many parents of the 10 to 12-year-olds were too scared about how the revelation would affect their relationship with the child.

Half said they had no intention of revealing the secret even when the child was much older.

However, several countries are considering giving children born after fertility treatments the right to find out their exact genetic background, which could mean the past coming back to haunt thousands of families across Europe.

Puberty threat

The evidence suggests that telling does not have an invidious effect on the relationship

Professor Susan Golombok

The figure was revealed by a massive psychological study into the welfare of IVF and donor insemination children and their families � timed as the children arrive at puberty, a traditional time when extra conflict and anxiety about their treatment could emerge.

On the whole, the research revealed that families with an IVF child were actually noticeably closer than families with naturally-conceived children.

In fact, even the fathers of donor insemination children, who might be expected to perhaps feel a little more distant from their genetically-unrelated children, scored highly as parents in terms of the warmth, affection and involvement they displayed.

Stable and contented

Professor Susan Golombok, director of the Family and Child Psychology Research Centre at City University in London, explained why families with IVF children might be more stable and contented.

She said: "They are people who really wanted to have children against all odds - sometimes they have spent 10 years having various investigations and treatments.

"They really value being parents and are very heavily committed to their children."

Even though most parents had not told their children about donor insemination, Professor Golombok's research suggests that they have little to fear.

She said: "The evidence suggests that telling does not have an invidious effect on the relationship - it may even have a beneficial effect."

She suggested that children born through donated sperm might be told in simple terms as soon as they could broadly understand the concept, perhaps even before school-age.

Many parents who chose not to tell were concerned, she said, that they would be able to give relatively little information about the biological parent - as sperm donation is carried out on an anonymous basis.