A woman has a right to bodily autonomy, but she does not have the right to kill a fetus. She does, however, have the right to remove the fetus from her body. There's a very real difference, and the fact that the fetus can't survive outside her is irrelevant
I've heard Libertarians make this argument before. They choose to base it in property rights. They say the fetus is a trespasser, and therefore the woman has the right to evict it, even if eviction results in death. In my view, this is nonsense. You cannot separate the performance of an action from its inevitable result. If you stow away in my plane, and I don't find you until after I take off, do I have the right to say, "You're trespassing on my plane. I have a right to remove you from my property, so you must disembark immediately. The fact that you will fall 30,000 feet to your death as a result is not my problem." No, of course not. I have to wait until the plane lands (the point of fetal viability) before I can evict the trespasser.
If the inevitable result of your action is death, the victim's right to life supercedes your right to take that action, unless failure to take that action will result in someone else's death. This is why even anti-abortion advocates generally support abortion in cases where the mother's life is at risk. If nobody's life is at risk, then everybody should have the chance to live. If both people's lives are at risk, the one who was there first (the mother) gets priority.
Even if we say the fetus has a right to bodily autonomy, you don't seem to know what bodily autonomy is. Bodily autonomy doesn't give you the right to another person's body. Per my analogy, I have a right to bodily autonomy, but that does not give me a right to your kidney. Even if a fetus has a right to bodily autonomy, that does not give it a right to the woman's body.
A fetus is an independent organism with its own DNA. It has a body, although that body is not fully formed. The topic of bodily autonomy becomes much more complex when one person has another person's body inside her own, but that doesn't mean a fetus doesn't have a right to bodily autonomy, as murder is the ultimate violation of bodily autonomy. The question is not whether a fetus has bodily autonomy, but rather at what point in the pregnancy does it gain that right, if the right is not created at conception.
Your example is comparing apples to oranges. You have no obligation to save the life of a stranger, but you surely have a higher level of obligation to your own offspring, and that obligation may supercede your right to bodily autonomy under certain circumstances.
Furthermore, comparing a pregnancy to a kidney (as I believe you've stated was your intent) doesn't work, because they're not equivalent. A person only has two kidneys, and while you can survive with only one, you will die if you lose both. A woman can complete a pregnancy without giving up any internal organs, and she can become pregnant multiple times during her life.
The entire abortion debate revolves around how to weigh the bodily autonomy right of a woman against the right of a fetus to live. Your position seems to be, "A woman has a right to bodily autonomy, therefore there are no other considerations." You have failed to demonstrate why a fetus's right to live is less important than a woman's right to bodily autonomy; you're just saying that it is, as if it's an obvious fact. It isn't, at least to people who oppose abortion. They would tell you that a fetus's right to live is more important than a woman's right to bodily autonomy, and your analogy doesn't explain why your position should be viewed as correct.