I have to disagree about the testing bit with autism; from what I understand, that doesn't even show up until a kid is a couple years old or more. Anecdotally, I have two friends with kids, and both their kids are mildly autistic. I think, in both cases, the mothers were in their early 30s.
>I guess they'll keep the population demographics at a sustainable level by immigration or something.
Yep, that's exactly what they're doing. The people having all the kids are either immigrants (esp. Hispanic ones), or ultra-religious Christians. All the people supporting "liberal" values aren't having any kids because it's too much time and money. So I think we can look forward to something somewhat similar to what happened to the Islamic world: it used to be at the forefront of science and math, and then turned into what it is today when the clerics took over.