How to tell our parents?

My husband and I are considering adoption. We are choosing adoption instead of having a biological child. I am an adult adoptee myself. Both of us have always felt strongly about adoption and I have never felt the urge to carry a child biologically as a paramount part of becoming a mother. As I mentioned, I am adoptee. I was adopted at birth, in a closed adoption. My parents adopted me as a last resort, however, after several failed IVF treatments. I was well loved, supported, and had a wonderful upbringing. However, my parents would've wanted to have a biological child if they could've, and only considered adoption when that wasn't possible.I think that, for that reason, they won't understand why my husband and I would chose adoption as first choice, rather than adoption as a last resort choice. I have brought it up in passing, and I have gotten the sense that they would wonder why I wouldn't want to have "my own." My husband's family doesn't have adopted members in it. My husband's sister has 3 biological children, and his brother is expecting his first biological child. I anticipate that they, too, will have questions and doubts about our decision. How can we handle these conversations with our parents? How can we steer the conversations in a positive manner? We would like our families to be on board, without having to justify our decision in detail (after all, if we had made the decision to have a biological child, we wouldn't be questioned or have to justify it or tell them about every pros/cons debate). Any guidance, thoughts, or suggestions would be appreciated. I am open to hearing your experiences with similar situations. Many thanks