Please go to the following website and see the section on Current Scientific Views of when human life begins, which is about halfway down the site document, after the section on Historical Views.
http://biology.franklincollege.edu/Bioweb/Biology/course_p/bioethics/When does human life begin.pdf
There, you will find a review of five different current scientific views - metabolic, genetic, embryological, neurological, and ecology. All are equally biological views and they all disagree.
There are also other points against this position. Not all zygotes are capable of developing even into embryos, much less surviving members of the human species outside the bodies of the women pregnant with them. Anywhere from 50-75% of zygotes/blastocysts die before implantation in the woman, and anywhere from 15-20% of implanted embryos of which the pregnant women are aware are spontaneously aborted, so that there is probably a rate of at least 20-25% spontaneous abortion for implanted embryos.
Furthermore, a blastocyst can divide into four and from each of the four an embryo can develop, and again that a blastocyst that implants results in both a placenta and an embryo. Again, an embryo may go through histogenesis and organogenesis, yet it may prove not to reach viability.
Sorry, but as long as the embryo lives parasitically in the woman's body and cannot live independently of that body, it is part of her body and her life. If you want it to be treated as separate, you'll have to detach and remove it. Oh, wait, that's what abortion does.