A lot of the family planning people agree that a baby is not a human until the fertilised egg has been implanted when it's about 6 days old.
So the fertilised egg alone is not enough to be a human. It has to be established as a pregnancy with the prospect of life.
Most medical people (including me) think that an abortion can be considered even when the baby is older than this if the mother's life or health is threatened by continuing with the pregnancy. But exactly how old the baby is before abortion cannot be considered is hard to decide.
Right to Life people think that abortion should never happen because it's wrong to put an end to the life of any human, no matter how young or old. There's no doubt that most Right to Life people have a great concern for life and living creatures. If every one respected life as much as they did people would be more careful and less unwanted pregnancies would occur.