A news tidbit from a few months ago: an Italian doctor that helped his terminally ill patient to die was acquitted of charges of performing euthanasia. His actions were in fact qualified as stopping treatment, which is something that every patient has the right to request. It was the case here. The patient, Piergiorgio Welby, suffered from an extremely painful condition (muscular distrophy).
The story brings forth a significant dichotomy that, I think, is important to understanding the boundaries of human life. Euthanasia vs. stopping treatment: in the first case, the patient is terminally ill, and highly uncomfortable, but is not actually dying. In the second, it is the constant work of medical machines and administration of drugs which is keeping the patient alive.
If a person is still alive only through the concentrated effort of technology, his life is somewhat less sacred that normally. Certainly the person himself has the right to request his death, and not even the Catholic church will find the request unreasonable.
(Whereas euthanasia, actively administering lethal drugs to a person that would probably die soon, but not quite yet, is highly illegal - because it is not only a crime against the person, but a crime against society.)
If this dichotomy is accepted as correct, it can be extrapolated to the abortion debate. The big question there is where human life begins. If we have established that it ends when the body cannot support itself - anything beyond that is borrowed time - then wouldn't it be reasonable to say that life begins at the moment when the body can support itself? The line at which abortion is immoral is the line at which the child could survive outside the mother's womb, without incubators.
Obviously there are complications, such as weighing the life of the mother against the life of the child, and there may be cases where the deadline is not so clear-cut. This is, of course, an issue that should be judged on the merits of each individual case: this is why we have sentience, reason and the capacity for analysis.
But it's a start.