My younger sister was adopted, I am our parents' natural child, but after me they realized that they would probably not be able to have more babies "of their own". My sister always knew she was adopted. In those days there was no possibility of contact with her biological mother.
As an adult she swithered for years as to whether she should or should not try to trace her biological mother and finally decided not to. My parents made it very clear to her that they thought it entirely natural she would want to know the circumstances of her birth and meet the woman who was her natural mother and that they would not be hurt at all if she did try to trace her.
Obviously, I don't know what my parents would have chosen had contact with the biological mother been possible when they adopted my sister.
I can say that when we were children my sister never asked about her biological mother or seemed particularly interested in the fact that she was adopted. And I would have known it if she had been curious, as I would have been the first person she spoke to about it.
We children were told that her mother had loved her, but had not been able to marry her father and had known she could not, as an unmarried mother in the 1950s give her child the life she wanted her to have and that she deserved and that was why she had given her up for adoption. My sister was told that with me and my brother, who died within seven hours of his birth, our parents had to take what they got as always when you have a baby yourself, but my sister was special as they chose her among four or five other babies because she was the most adorable.
Daddy especially felt that adopted children should be brought up knowing they were adopted, as the shock of discovering it as an adult, or whenever a child poking into a drawer came across the adoption papers could do untold damage.
My sister was my sister (she died of cancer two years ago) she could not have been more my sister (or I hers) if we had been born of the same parents, and I felt hurt on her behalf, when she had to bring along the adoption papers when we were settling first Mummy's and later Daddy's estates. I felt that she was legally my sister, and at that late date the fact that physically we were born of different people should not have mattered.
Frankly, I feel contact between the adult parties to an adoption is more for the benefit of the natural mother than for either the adoptive parents or the child concerned. Most women who have lost a child, whether by given him or her up for adoption, to death or by electing for an abortion are always going to have days where they think "What if?" Knowing you have a child somewhere and not knowing how that child is, must be horrible, so I understand the suggestion of contacting the natural mother once a year or so with information. Only the woman concerned can know if that helps her or the reverse.