The basic problem is that this new life is constantly and rapidly changing. At the moment of conception it's just one cell and can't be seen without a microscope. By the moment of birth almost everyone would agree that it's a little person, a protected member of the human community. The question at the heart of this great controversy is whether our moral obligations to that cell are essentially the same as they are to the little person. I find it strange to think that they are, although it is obvious that under the right conditions the cell will grow into the little person.
Many people disagree.
To them, deliberately ending the life of the cell is no different from killing the little person. Clearly, your decision about what to do about your pregnancy depends largely on which point of view you take.