By Caroline Ryan
BBC News Online health staff in Berlin
Only a third of couples who conceived their children using donor embryos plan to tell them, research suggests.
Parents fear upsetting children conceived using donor embryos
Researchers at City University, London, found many of the 21 families they asked feared revealing the information could cause distress within the family.
In contrast, 90% of 30 IVF families and 100% of 28 adoptive families surveyed said they would tell their children about their origins.
The research was presented to the European fertility meeting in Berlin.
The study looked at 21 families with a child conceived through embryo donation - where surplus embryos from IVF procedures are donated to infertile couples.
It also looked at 28 families with children adopted as babies, and 30 families with children conceived through IVF.
All parents were interviewed and completed questionnaires when the children were aged between two and five.
The research found there was no difference between the three groups in terms of parental warmth and the quality of parenting.
But couples who used donor embryos did appear to be likely to be more emotionally involved with their children.
Fiona MacCallum, a research psychologist at the Family and Child Psychology Centre, City University, London, UK, said: "The most common reasons for not telling the child about their method of creation were fears that it would upset the child or damage family relationships.
"And there was also a feeling that, since the mother carried and gave birth to the child, she was the real mother and so there was no need to tell the child anything different."
Ms MacCallum said the fact parental warmth and quality of parenting was similar in all three groups showed "it is the level of commitment to parenting that is important, and not the presence or absence of biological links between parent and children".
But she said: "Embryo donation parents obtained significantly higher scores on measures of emotional over-involvement and defensive responding than did the adoptive or IVF parents."
To assess emotional over-involvement, the researchers looked at the extent to which family life centred on the child, and whether the mother was happy to leave her child with others and whether she has interests which are not related to the child.
A spokeswoman for the charity Infertility Network UK said: "You cannot underestimate the trauma of couples who experience infertility, and especially those who may have gone down every other route before using embryo donation.
"Making a decision to tell their children about their origins can be much more difficult for couples who have conceived through embryo donation because the baby does not have either of their genetic backgrounds.
"With sperm or egg donation, 50% of the genes will belong to the mother or the father. Embryo donation couples have none of that ownership.
"We have to respect the decisions of couples about what they tell their