Anytime anyone is ever injured or ill, the medical establishment is faced with the job of assessing what is necessary, what is viable. They make those decisions for patients on a day to day basis. I don't see where a fetus would be any different than any other person who enters a hospital. I'm not sure where the line is that a fairly regular survival rate occurs is, but, when I was going through my pregnancies, we were often given the 20 week and 2 lb marks as the points past which we could breathe a bit easier, as a 'miscarriage' is now termed a 'premie', and survival rates are much improved. I threw out 30 weeks to be on the conservative side. I'm no doctor though, and won't pretend to be one.