This might be helpful for those inquiring as to when a fetus is a life. I read this a while ago and I found it very interesting. I just thought that maybe it would be a good thing to post here.
"Life begins at conception. At that moment a new human being with a unique genetic blueprint has come into existence."
1) There is no scientific consensus as to when human life begins, a point made by such institutions as the National Academy of Sciences and the American Medical Association.1 These scientists say that the point at which a new person comes into existence cannot be scientifically discovered; it is a matter of philosophic opinion or religious belief, not scientific fact. It requires a judgment of what we consider a human being to be. For instance, does a human being consist of genetic information, or a disembodied soul, or a consciousness in a body? Or is it a separate, social being who has been born?
2) Biologists tell us that all life comes from pre-existing life. In other words, life does not begin, it is transmitted. The human egg and sperm are both living, human cells. At conception, two previously existing living things come together to form another living thing. Therefore, fertilization is not the beginning of human life, but is a significant step in its continuity.2
3) There is no "moment of conception"; conception is not a momentary event but a multi-step process which happens over a 24 hour period.3 Up to two weeks later, a twin zygote can form by breaking away from the first. Pregnancy is not considered to begin until the fertilized egg implants in the woman's uterus, approximately two weeks after fertilization.4
4) At least two-thirds of all human conceptions are spontaneously aborted by nature.2,5 In other words, most "unique genetic blueprints" stop developing naturally, and no one seems to consider these to be "human beings".
5) As the discussion document of the Canadian Medical Association's Committee on Ethics points out, the claim that a human being exists at conception equates a potential with an actual: it assumes that because a fertilized egg has the biological potential to develop into a human being, it is one already.6 This is like saying that an acorn is the same as an oak tree or a fertilized hen's egg is the same as a chicken.7 This ignores the very fundamental difference between the present material natures of the two. The difference between the potential of an early pregnancy and an actual person was traditionally recognized by the Judaeo-Christian Islamic religions.6
6) Only genetic individuality - a set of inherited tendencies or predispositions - is present at conception.4 (Genetic individuality is a characteristic not only of humans but of all living things.) A human genotype is not the same as a person; tumours that grow in the human body carry as "unique" a "genetic blueprint" as does a new conception.2
7) There does not seem to be any "blueprint" for the development of the embryo. The fertilized egg may follow many different paths; each step in its development depends upon the pattern of cells and molecules just reached in the preceding step. Identical twins, for instance, grow from the same egg, have exactly the same DNA and develop in the same womb, yet they are different - they even have different fingerprints. In rare instances a second or third embryo will start to develop one body part but not others, and end up as a cyst with remnants of body parts, such as teeth, bones or other organs.8 The fertilized egg is clearly not a prepackaged human being.9

According to embryologist Clifford Grobstein, there are five other essential aspects of individuality still to come after fertilization: developmental, functional, behavioural, psychic and social. This means that full individuality emerges in stages over time.4
9) The human brain is considered central to what it means to be human and alive. Scientists state that the nature of our cerebral cortex, or the thinking portion of our brain, is what makes human beings different from other animals.2
The Canadian Medical Association's Committee on Ethics,6 as well as many international scientists and theologians,2 have identified the birth of fetal 'brain life' as the beginning of the life of a new human person. Fetal brain life has been defined as the capacity of the cerebral cortex "to begin to develop consciousness, self-awareness, and other generally recognized cerebral functions as a consequence of the formation of nerve cell circuits".10 This process is usually defined as occurring sometime after the 24-26th week of pregnancy,2,4,10 although the Canadian Medical Association's discussion paper sets a more conservative date of 20 weeks.6
Also, 23-24 weeks is about the same stage at which a fetus may potentially survive outside the womb if born prematurely.11,12 Scientists say that the threshold of survivability has stabilized and will not change in the foreseeable future (despite a massive increase in medical capability), due to the timetable of fetal development.12
10) The transition of childbirth is different in quality from previous stages of development. The fetus leaves the woman's body in a multi-stage process, enters the world, breathes for the first time, uses new senses and organs, and exists independent of its mother. When a baby is born its voice is heard, and within hours of being born there is a necessity to communicate.
Birth marks a critical point in the biography of an individual; it is the moment of social membership into the family, community, culture, and, ultimately, history. Professor Thelma McCormack points out that the difference between "unborn" and born is not a slight developmental change, but an enormous existential one. This is true for both infant and mother. "Life truly begins."13
11) Even if it could be shown that human life begins at conception, that finding would not entail the further moral judgment that life at that stage ethically merits full protection. When human life begins and when human life, once begun, merits or requires full respect are two different questions.
http://www.caral.ca/facts/responses.php