Fear of rejection and concerns about the reaction of the child prevent many parents from telling their children they have been conceived with donated sperm, scientists said on Wednesday.

Despite changing attitudes, a trend towards more openness and laws in some nations identifying donors, researchers at City University in London said even couples who intend to tell their children about their origins often do not manage to do it.

“Intention is not necessarily followed through,” said Dr Emma Lycett, who reported the results in the journal Human Reproduction.

“People who did not want to disclose felt it was irrelevant, or their infertility was personal to them. They wanted to protect the child,” she added in an interview. Lycett and her colleagues interviewed 46 families in England with a child up to age of 8 who had been conceived through sperm donation. Thirteen percent had already told their child and 26 percent said they intended to.

But 43 percent decided against it and 17 percent were still unsure what they would do.

“An earlier European study of parents in this age group found that fewer than 10 percent had told their child by the time they had reached early adolescence,” said Lycett.

Parents in the latest study who told their children cited honesty and a fear of accidental discovery as the main reasons. But nearly 30 percent opted for secrecy because they feared it would damage the relationship of the father and child.

In a separate study in the journal, Dr Anne Brewaeys of Leiden University Medical Centre in the Netherlands questioned 105 couples who were looking for a sperm donor.

Last June, the country made it compulsory for sperm donors to be identified. Couples at the university’s fertility centre can select an anonymous donor or one whose identity will be revealed when the child is 16 years old.

Britain will introduce a similar law later this year.

The majority of the heterosexual couples chose an identifiable donor and all but one of the lesbian couples opted to know who the donor was.

“Motives for choosing an identifiable donor were the same for heterosexual and lesbian couples,” said Brewaeys.

“The majority pointed to the right of the child to know its genetic origins. Although most parents did not want to be involved with the donor, they decided it was not for them to block the child’s access to donor information.”

Heterosexual couples with lower socioeconomic status and those who had difficulty coping with male infertility were more likely to select anonymous donors.