Late-term abortion: the life of the other twin
To add to Anna L's info, one point that is consistently left out of statements like Feddie's (and most lists of "permissable reasons to have abortions, maybe, if you beg hard") is, "the life of the other twin."
Intact dilation & extraction (mis-named "partial birth abortion"), for instance, is generally the best way to get a dead or dying twin out of the uterus while leaving the other twin safely in the warm for a few more months. Without such procedures, the death of one twin late in pregnancy would normally mean the death of both.
Of course late-term abortions make you queasy. Medical procedures often do. The reason they probably don't make me as queasy as they do you is that I've read 19th-century obstetric manuals and seen their medical instruments, and you have *no idea* how queasy you can get.
If the fetus is viable by that time, and the mother's life is at stake,Not usually, because:
wouldn't an emergency caesarean address both problems?
1) often the fetus is not viable -- it may have no brain, for instance.
2) even when it is, "viable" means "50% chance of dying, 50% chance of living with major medical problems." You aren't generally going to get a healthy baby out.
3) a Caesarian is itself life-threatening. If the woman's life is at stake, one reason may be that a Caesarian will likely kill her. Caesarians are *major* surgery, with all the risks that entails -- blood loss, general anaesthesia, cutting muscles apart.
4) what about the cases with twins?
No-one is having late-term abortions because they *like* killing babies. They're doing it because it's a way of maximizing the number of healthy people you'll have by the end.