We have known many Downs kids and others with severe cognitive issues. My wife served as a board member for the largest facility that assists adults and their families with these types of issues. That said, knowing the actual difficulties trying to take care of such a child for their entire lives is daunting. No one who has not been through this type of challenge has a clue as to how much of a burden this type of situation creates.
So, although these numbers are horrific, they are certainly no surprise if you look at the current generations that are now in their childbearing years. This is especially the case because most people in our society put off having kids until they are in their 30s and beyond. Both my wife and her sister were born when their mother was in their 40s and that was in the late 1950s. But the trend has gotten much more prevalent at least for most demographics.
The chance of having a Downs kid when the mother is in her 40s are much greater when the mother is younger. A woman aged 25 has a chance of 1 in 2500 of conceiving a downs baby. When she is 40 it is 1 in 100, by the time she is 45 the chances increase to 1 in 30.
https://www.health.state.mn.us/diseases/cy/downsyndrome.html
My wife and I have known many women who at around age 40 decided they wanted to have a baby. Even the most pi0us of those would likely to choose to have an abortion rather than facing a future of spending their elderly years trying to take care of a young adult with Down’s Syndrome.
I have grown child with a learning disability to the extent that he will never be able to live on his own. The core issue is that pre-born DS children are already human beings. When is it right to deliberately kill a helpless human being that you have conceived because they will be inconvenient to you?