its not that blurred. there's two definite defining points we can work from, conception and birth. there's only a lot of grey if one doesn't accept the latter, and the acceptance of the former is not credible. for majority of the gestation the embryo/fetus is not remote viable outside the womb, we have only pushed that back some weeks with modern medical intervention.
Except tonnes of people believe all different parts inbetween, as to when is acceptable to abort. It's a huge grey area hence the endless debates.