Fetuses are generally viable thanks to medical progress we've made in the past 20 years or so at roughly 5 months, just over the halfway mark. A friend of mine back in the late 90s had a child 5 months early, he's a healthy lad going on fourteen or so years old today. I'm fine with setting a limit on open access to abortion at this point, meaning any abortions after that point would require medical approval based on the premise that the child is potentially harmful to the mother's health, or the child is so severely malformed that it is not ever going to be viable outside the womb, such as the case of a child whose brain never develops. This would also give leeway for the types of anomalies in chronology that are inherent in the birthing process that Etoille is pointing out.
There's definitely a ton of grey area, the cognitive point of view is as profoundly flawed as any view on when life begins, though, because you really don't become "Self aware" until almost two years after birth, as the Journal of Medical Ethics argued, thus by that view, post partum abortions up to 2 years of age would/should be legal.
I don't think anyone in this thread would argue that we should be able to abort, say, a 1 year old child, but that argument has been legitimately made in medical ethical journals before, so we should be aware of the reductio ad absurdum inherent in the "Well if you don't have cognition of yourself, then you are not alive/a human being" argument.
Incest and rape are traumatic experiences and abortion should probably almost always be allowed in those cases, but it gets a little hairy/into a case-by-case basis when you start asking "Well if a woman is raped, and reports it, and then decides to keep the child until the 7th month, should she then be allowed to abort it at that point?" then I dunno what the answer should be, because that shit is just too complicated and too inherently based in each individual case to really build up a personal opinion on the subject.
I posted this earlier in the thread, but its a good article and worth reading and thinking about when you think about abortion and how mindset/worldview can influence how/when someone feels abortion is justified versus when it is not.
http://www.slate.com/articles/health...anticide_.html
This next link should be directly to the journal article that argued for post partum abortion, so you can read the logic behind it yourself. Note that the medical ethicists making this argument probably don't agree with it themselves, but they were making the case for academic reasons.
http://jme.bmj.com/content/early/201...11-100411.full
There's really no way to say "This is the point past which we shouldn't be allowed to abort" that won't, by necessity, be at least a bit arbitrary. And I'm not a huge fan of the government regulating behavior like abortions, but I think if everyone had to sit down at a table and discuss a compromise on the exact time past which access to abortion should be restricted to medical necessity, somewhere between month 4 and 6 of the pregnancy would be where we ended up at, and I'm okay with that.