The fetus can’t be given rights to the mother’s blood or use of her body, otherwise that sets a pretty dangerous precedent. If abortions can be outlawed, why not vasectomies? Or chemotherapy?
My point is it doesn’t matter the status of the fetus. It’s about the right of pregnant women to have autonomy over their body.
The thing is that a lot of people think that a fetus is a person with rights. If a fetus is a person with rights then bodily autonomy doesn't quite apply. The bodily autonomy angle seems more of an escape hatch to sidestep the subjective and unsolvable issue of whether or not fetuses are people and have rights.
I'm pro-choice btw
Your knife example has nothing to do with your bodily autonomy. It’s why you can’t be forced to donate a kidney or why you can choose to get a vasectomy.