I don't believe anyone in the scientific community is saying that. I think people who are debating prochoice sometimes get frustrated and make poor arguments like this in a desperate attempt to get people to understand. A human fetus in indeed human and also alive, but it's not "viable" until over halfway into the pregnancy, which by then is where elective abortions have already ceased to legal and only rare late term abortions are done in extreme life-threatening medical situations.(1)