I honestly hope the baby is not born; a baby would jump Dexter over the shark.
Even a girl baby? I'm not afraid of this baby like a sitcom baby. I don't think it's a death knell.
As for the obvious that turns out not to be so, I can't think of what the obvious might be. But I am totally seeing attraction between Deb and Anton, and I'm not sure if I'm looking for it or if it's really there.
How did he meet Dexter's sister?
At the hospital for the guy whose legs he chopped off. But he was clearly just using Deb to get to Dexter, so he would have found a way to do it somehow. It probably wasn't too hard to get the victim to a place that the cops would be visiting and that he would have reason to frequent.