The legal systems of a given country need to recognize the human nature of the unborn. This means that murder involving the unborn should be treated the same as murder involving anyone else.
The current procedure is innocent until proven guilty. Obviously if the defense maintains mental insanity, manslaughter, accidental death, coersion or what have you, the burden of proof shifts to the defendent, however it should still be no different from how the murder of other human beings is prosecuted.
The same penalties should apply as with murder of any other human being, assuming the current penalties for commiting murder were sufficient.