The title speaks for itself. Besides the fact that it's just plain sickening to consider an unborn child as such; those who use this phrase are simply wrong. A parasite is defined as an organism that lives on or in an organism OF ANOTHER SPECIES, known as the host, from the body of which it obtains nutriment.
Unless it is humanly possible for women to give birth to something besides a human baby, your unborn child is not a parasite. So please stop using this as a means to prove your pro-choice agenda. You sound ridiculous.