So then, you are an extremist. There is no other way to describe this position.
Abortion rights are based on a woman choosing not to remain pregnant, for whatever reason. They're not based specifically on some kind of inalienable moral right to end a life because it happens to be located in your uterus.
There is no physical or moral difference between a slightly premature baby (or foetus? I don't know if the terminology changes at birth or at a specific stage of development?) born around 39 weeks and a foetus in the womb at 39 weeks, and the woman in this scenario has already been pregnant for almost 9 months and will have to give birth either way.
I understand this would be an extremely unusual situation and almost zero women would choose an abortion at this gestation, although it's probably naive to think the number would be zero. But even as a thought experiment or a theoretical principle, it's harmful.
I'm pro-choice but this fundamentalist viewpoint of 'as late as necessary' just fuels the pro-life brigade who love to characterise women as morally vacuous baby killers. There is a balance in the law based on viability (and in fact other developmental markers that correspond with viability), allowing time for a woman to be aware that she is pregnant and make the choice to terminate, and acknowledging abortion as a protective measure for a woman's mental and/or physical health. None of that means there isn't another life involved, it simply means that pregnancy is a specific scenario in which that life is
a) at an early, non-viable developmental stage, absent a functioning nervous system/sentience etc.
and
b) entirely reliant on a woman's body, a woman who may be physically or psychologically unable to continue or, yes, simply not want to be pregnant anymore (although the latter reason is not given in law which I would argue it should be.)
These factors are balanced against the status of the foetus at different stages of development and the cut-off point is probably about right IMO as far as the law is concerned, and of course this does not apply in cases where the life of the mother is at risk during either pregnancy or birth.
What you're saying is, a woman's right to choose is a woman's right to end a life but actually it's her right to end a pregnancy that is the question. In a situation where the pregnancy is all but over anyway you are simply advocating for infanticide.