I am AS, first born, not only child. My son is AS, first born and only child. There's a little truth to the difficulty encouraging parents to not have anymore. My son had pretty severe sensory integration issues. I was pregnant after him, but miscarried. Then I left his dad. Just never met anyone else that I wanted to have kids with and had so much stuff with my son, I was already worn out. Now, my husband had "the operation", and two grown children, so he was waiting for grandchildren. Just seemed silly to go back to diapers. Also, son hit puberty and I knew the chances of having another kid on the spectrum was very high, so it just didn't seem like it was important anymore. I was trying to finish my education. I guess life got in the way.
_________________
"All those things that you taught me to fear
I've got them in my garden now
And you're not welcome here" ---Poe