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More than 10 years after meeting their birth mothers, adopted children are still "walking on eggshells" around them.
That's the finding of research by Massey University student Julee Browning, who has made what she believes is the first study of the long-term consequences of reuniting adopted children with their birth families in adulthood.
New Zealand was the first Western country to allow adopted children to contact their birth parents, under a law passed in 1985. Since then, 31,186 adoptees have used the law to get their original birth certificates, and 8648 birth parents have obtained identifying information about their adopted children.
Ms Browning interviewed 16 women and four men, aged between 26 and 71, who had been in contact with their birth parents for at least a decade.
She found that, even after many years, adults who had been adopted out as children almost never felt completely at home in the families of their birth parents.
"People struggled to communicate their needs to each other. That did surprise me," she said.
"There is this walking on eggshells to some degree. Even after 20 years, people are still careful not to disrupt the relationship. Although people can be upset by each other, they are more likely to retreat from a fight and come back rather than confront any problems."
In four cases, both birth parents of the people Ms Browning interviewed were still living together when they were reunited with their adopted children as adults.
But even in those cases, the adopted children did not feel fully included in their birth families.
"I think you are always on the outer," said one adoptee, "Sarah" (names changed for anonymity).
"You probably get this idea of how it could have been because they [birth siblings] connect so much better than I do. It's that whole history thing. It leaves me feeling dissatisfied all the time, like you are part of the family but not really."
The adoptees sometimes wanted to be included in their birth families' family events such as Christmas and funerals, but often that was not possible because birth parents did not want the child's existence widely known.
One adoptee who was not invited to her birth grandfather's funeral was "deeply hurt and confused".
Another went to her grandfather's funeral but was not invited to give a eulogy along with her birth brothers and sisters.
"She found that very difficult because she was not able to join in."
On the other hand, some of the same adoptees who felt excluded from some family events felt compelled to go to others which they did not really want to go to, because otherwise the invitations might stop coming.
Christmas Day was a challenge for some because "one mother would be disappointed".
"There is this oscillation backwards and forwards as to do they become family members?" Ms Browning said.
"There isn't a relationship model, so it has been found that it is most like aunt/niece, aunt/nephew, uncle/niece or uncle/nephew in that there is that connection but it's not going to the degree of mother/child or father/child."
Usually the first connection was to the birth mother, although in one case the mother had died by the time the contact was made. Many never made contact with their birth fathers.
"The birth father's details are generally not held because he is the 'alleged father'," Ms Browning said.
"Finding the birth father has not been a priority and has a 'maybe-sometime-in-the-future' or 'I don't have sufficient information right now'."
Women were also much more likely than men to make contact.
Sixty per cent of adopted children contacting their birth parents in the past 20 years, and 89 per cent of birth parents contacting their adopted children, were women.
Ms Browning said that many adopted children found their birth mothers needed a lot of emotional support.
Many never saw their babies before they were taken away for adoption in the era when unmarried mothers were regarded as sinful, and met them for the first time as adults after the law was changed in 1985.
"Many of them feel the birth mother needs more from them, and others are saying they don't get enough from her. Some feel the birth mother is too needy and they pull back."
Adoptions have become much less common since the domestic purposes benefit was introduced in the 1970s.
* In 1985, New Zealand became the first Western country to allow adopted children to contact birth parents.
* Since then, 31,186 adoptees have used the law to get their original birth certificates, and 8648 birth parents have obtained identifying information about their adopted children.
* Adoptions have dropped from a peak of 4000 a year about 1970 to 323 last year.