Help me understand...

If a man kills a woman and her unborn child, he is guilty of a double homicide, because the unborn child is a person and the definition of homicide is the killing of a person by another person.

If a man shoots a pregnant woman and she lives but her child dies, he is guilty of homicide because the unborn child is a person.

If a woman kills her unborn child it is not a crime at all.

If a woman allows a medical doctor to partially deliver and then kill the full-term but unborn child, there is no crime. Why then could not the doctor completely deliver the baby and then kill it? Would it then be homicide because it occurred seconds later than the partial-birth abortion?

Why can't the mother take the baby home and kill it without committing a crime (which was the practice for centuries in China, particularly if the child were a girl? And is it criminal to selectively abort girl babies (as is now commonly done in China)?

Can anybody help me understand these things?