My preferred system is similar to Canada's, where a national healthcare system pays for any abortion a woman has, at any time, on request, anywhere. Most of the debate on third term sentience comes from scientists who are already established in their belief that abortion is wrong and they simply search for data and interpret results in a manner that favors their own point of view. Even if we can't answer the question with absolute certainty, that doesn't mean something we're reasonably sure of shouldn't be the basis of our own policy. Many of Einstein's theories can't be verified with absolute certainty,  yet we still use his work as the basis of many modern scientific fields. Even if only a few women get third trimester abortions, these women obviously feel that they need to get these abortions, and whether they do or not is something I believe should be left solely to a woman, not some judge or bureaucrat in a hospital, business or government office. Whether she chose to have sex or not shouldn't play into it either. The entire idea of judging women, or indeed anyone, based on their sexual choices is absurd and simply an attempt at social engineering to limit freedom. The data I posted shows that there is reasonably conclusive evidence on the sentience of a fetus in third trimester, and that most women who get late abortions do so because they honestly do not know whether they are pregnant or not. Stating the opposite means nothing without data to back you up.

As for the source of my data, a history of reading, and some quality Google and Wikipedia-fu.

Second:

Why do you believe a woman under 18, who is already considered responsible enough to make sexual choices (at least if you're not living in some backwater state with an age of consent set at 18), should have to ask her parents to get an abortion? She already decides what goes in her body when she eats and drinks, shouldn't she have the ability to decide whether a fetus should stay in her body too? Imagine you were pregnant, and your parents were hyper religious nutjobs who hated people who got abortions. Wouldn't you feel discriminated against?

The major reason clinics don't do it is because of the threats to the lives of people who do do it and because of the restrictions by law on these sorts of abortions. It has little to do with whether the procedure is safe or not. Anyways, shouldn't we live the choice of whether to go through with a risky procedure or not up to the patient? Are they not the only people who should have control over their own lives? And, as the data shows, a majority of woman get late term abortions because they do not know they're pregnant. This is obviously a problem among women, and simply denying that it exists without any supporting data does nothing to further your cause.

How the fetus looks quite literally means very little. As they say, looks can be deceiving. There is a case for banning the killing of a creature that is intelligent and sentient, that can use tools, that can understand language and count, that can feel pain and understand the pain of others, like a cetacean. A fetus can do none of these. It doesn't think, it doesn't feel, it doesn't understand, it doesn't experience, because it is unconscious. It is no different than the microbes you likely kill every day, even though it doesn't look like any of them. Feeling and look and other feeble emotions matter nothing in this; only scientific data should be taken into account.