FETUS IS NOT A BABY (GOOGLE THE HUMAN
DEVELOPMENT CHART), but a parasite because the classification of the biological relationship that is based on the behavior one organism (fetus) and how it relates to the woman's body.
as a zygote, it invaded the woman's uterus using its TROPHOBLAST cells, hijacked her immune system by using NEUROKININ B and HCG--- so her body doesn't kill it, steals her nutrients to survive, and causes her harm or potential death.
http://en.wikipedia.