The mother knowingly bought the danger unto herself by choosing to become pregnant. Therefore, she is not acting in pure self-defence. As a result, abortions carried out to save the mother's life are not an act of self-defence and should not be permitted.
Even in cases where the mother's life is at risk, neither the parents nor the doctor should be permitted to take any measures that would deliberately end one or the other's life. The physician has the responsibility to do everything in his or her power to save both lives. If the child dies as an unintended consequence of treatment, then this is not an abortion and the physician and parents are morally justified. However, if the child is deliberately killed, this is unacceptable and there must be legal sanctions in place to punish those responsible.