The right to do what you want with your body

For many people it is obvious that when you want to have a procedure to remove a fetus from your body in order to destroy a life, you can because you control you body.

But if you want to have surgery to remove a kidney from your body in order to save a life, you can't because you aren't allowed to decide what to do with your body.

I guess it has something to do with the fact that the kidney is "part of you" and belongs inside you whereas the fetus is another person that does not. But if you're going to acknowledge that the fetus isn't part of you, then aren't you acknowledging that it isn't part of your body?