Children requiring blood or other donations from their caregivers is not a normal state of affairs, so our policies in that regard are not very extensively developed. In particular, having a child as a dependent generally does not come with the assumption that you will have to donate blood to them. If it was a central part of raising children, we'd probably have different rules. As it is, the rules we do have result in the successful raising of children under almost all normal circumstances.

However, gestating a child is an essential part of creating a new person. As much as we might wish it were otherwise, the biological demands are not equal between men and women. We can try to compensate, but we can't make the two scenarios physically identical.

Let me give an example of how we create unique rules in this area because of its central importance and the constraints of biology. Normally, one person cannot force another person to pay for an expense that is their choice. However, in places where abortion is legal, a woman can choose not to get an abortion, and the man who got her pregnant is unavoidably on the hook for ~$100k child support payments (lifetime average). There is nothing he can do to get out of it. He can't give the financial responsibility up for adoption. He can't force the woman to get an abortion. Her choice, his responsibility.

Now, if you think this is financial slavery and the policy should be ended immediately, I grant that you are at least consistent in your views. But even then, it shows that we treat birth with special rules. You cannot simply find some principle that generally applies elsewhere and assume that it also applies in the case where new babies and children are involved.

So you can declare that you think bodily autonomy trumps all other concerns. But don't expect that people will agree that because you place that as the highest principle that everyone else will agree that it trumps the life of a dependent. Indeed, when it comes to intervening--and make no mistake about it, an abortion is absolutely an intervention--we can find all kinds of cases where ordinary actions (like driving down the road) are curtailed when someone's life might be in danger (you can't run over pedestrians, even if you're bleeding to death and trying to get to the hospital yourself).

Furthermore, a negative right that prevents others from doing stuff to your body is different from both a positive right to do stuff to your body (e.g. there are, in some places, laws against self-mutilation, and there are certainly laws against self-medication with certain substances).

Pregnancy is a unique situation in multiple ways. Therefore, although we can use analogies to inform the decision, it has to be made on its own merits.