And could lead to faking by women who didn't want to have any more kids, maybe...

I've read this before, and I always wonder how many people really believed it to be infallible, even if it was considered a valid medical fact. The same way some people now don't really believe that tanning booths and smoking cause cancer, no matter how many times their doctor tells them. Or, for that matter, the fact that we "know" you won't get pregnant if you use birth control, and yet everybody also knows there's a chance you will. I guess in a larger sense I'm wondering what impact not having the scientific method or statistics or probability had on the strength which with people held beliefs about things being possible/impossible.

It could explain a lot about Leontes' irrational jealousy in The Winter's Tale, though. I wonder if anyone's thought of that before?