Is it rue that Pro-Choice allows a pregnant woman to abort the fetus any time she wants to?

Since the fetuses health also depends on the health of the mother, based on the fact that a mother can do anything with her body, what's her resonsibility towards the fetus if she decides to abuse her body such as doing drugs? If a pregnant woman gets killed, why is the law charging the perpetrator for double murder, the mother and the fetus, since I suppose the fetus was not a person?