Your philosophical distinction is clear enough, but in practice it can't hold any weight until we perfect the practice of mind-reading. If the right to choose is the woman's, obviously as science increases its capacity to reveal more about the fetus, this information informs, or deforms, the decision to proceed to pregnancy.
The odiousness of birth selection according to sex, disability, etc. is a social one, but it has no concrete expression unless the fetus has some autonomy. Suppose there was incontrovertible proof that Ms. X planned to abort because the fetus had been determined to be unsatisfactory to her in some way stemming from prejudices we would all see as venal. The law can either ratify or protect this act, or seek to sanction it. If the latter, then choice or rights must be less than absolute.
mbs