Researchers surveyed 72 parents of 66 children who had been conceived using donor eggs. The children, from 46 families, ranged in age from 7 to 19 years old at the time of the survey.

Previous studies have focused on parental intentions to disclose but not on what actually occurred in the disclosure process, the researchers note in the journal Human Reproduction.

Twenty of the 46 families had disclosed to their children that an egg donor was used in their conception. The average age of the children when they heard the news was five and a half, but ages at disclosure ranged from 1 to 13 years.

"Families disclosing to children by the age of 8 reported the lowest levels of conflict regarding the disclosure process and the highest levels of satisfaction at having disclosed early," the authors write.

They also found that parents reported feeling more anxious about disclosure the longer they waited.

"Waiting for the `right` time to disclose can inadvertently lead to prolonged/unintended delays and heightened parental anxiety as children get older and they are faced with disclosing to adolescents or even older children," coauthor Nancy Kaufman, a licensed clinical social worker in private practice in New York City, told Reuters Health by email.

"We were most surprised by the number of parents who despite wanting to be open and honest with their children have delayed disclosure," said lead author Linda Applegarth of Weill Cornell Medical College in New York City.

Of the 26 families that had yet to disclose the information, 18 still planned to do so. The average age of the children in this group was 11 years old. At this age, they are "close to the teen years where there might be more resentment about not being told earlier, and parents worry about this," Applegarth said.

Primary reasons for disclosure were the child`s right to know, the desire to be open and honest and the notion that family secrets are harmful. For families who still intended to disclose, primary reasons for delayed disclosure included never finding the right time and uncertainty about how to disclose.

Half of the families that had already disclosed the information had sought mental health assistance, compared to only two of the 18 families that still planned to disclose but hadn`t yet accomplished it.

The study had limitations. For example, only 12 percent of those who were invited to participate actually did. The researchers had originally mailed invitations to 459 families to attend a seminar on disclosure in egg donation at which the survey was administered, but only 46 families sent representatives.

In many cases, the addresses may not have been up to date, Applegarth said.

The investigators clearly state that this is a preliminary study, said Patricia Hershberger of the College of Nursing at the University of Illinois at Chicago. Still, Hershberger said, the seminar might have affected the parents` attitudes and perceptions about disclosure.

Nevertheless, the study "provides much needed insight into understanding how parents in the U.S. approach disclosing the true conceptual origins to their donor-egg conceived children," Hershberger said.

"The findings have implications for both parents and healthcare practitioners," she added. "For parents, the findings encourage early disclosure and for practitioners, the findings suggest that follow-up is important, especially for some parents. Which parents can best be helped by follow-up is yet to be determined and an area for future research."

Applegarth said parents who attended the seminar felt it was helpful to meet other families in the same situation. She hopes reproductive clinics will focus more on support services for families.

Parents should also seek out clinics that will help them with future conversations, Applegarth said.

"Families are very attached to where they got their children," and there`s comfort in returning to the clinic for help with difficult conversations, she said.

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