The Sages arrived at their point of view from the statement in the Book of Exodus [21:22] that if a pregnant woman is struck by someone, and her unborn child is destroyed, the person who caused the mishap must pay damages. He is not, however, considered a murderer because the unborn child is not a person. The Talmud is quite specific in describing the status of an unborn child: "If a woman is having difficulty giving birth and her life is in danger, the fetus may be removed surgically, limb by limb, because her life takes precedence over the unborn fetus. However, if the delivery of the child has already begun, and its head or the greater part of its body has already emerged, the child may not be harmed to save the mother, because one person's life may not be take to save another."
As one rabbi has said "So long as the fetus does not enter the 'atmosphere of the world' it is not considered a person." However, despite the fact that in Jewish law the unborn child is not considered a person, the law does not approve of abortion unless there is sufficient justification.