In the case of an ectopic preganancy (this is where the embryo implants itself somepalce other than in the uterine wall, usually the wall of the uterine tube) there is never a chance the developing child will live, it will always die. Also, if the embryo is not removed, i.e. aborted, the mother faces serious health risks, even death, if the uterine tube ruptures. In this situation what is the Churchs teaching on the proper course of action?
Abortion is always evil - it intends to directly kill a child. It is never allowed even to save the life of the mother. The Church clearly teaches that “One may never do evil so that good may result from it” (Catechism, 1789).
However, in the case you describe, the mother’s malfunctioning organ (fallopian tube, or a portion of it), may be morally removed to eliminate the risk to the mother. The intent here is to remove an organ that is about to rupture (no different than if a tumor was there). To not do so would be life threatening to the mother. It is unfortunate that the threat happens to be caused by an abnormal pregnancy. If the child dies his or her death is not directly intended but is tolerated as an unintended consequence. (In the future it might be possible to implant such a child into the uterus. Until such time, however, the procedure is still moral.)
For consultation in such matters contact the National Catholic Bioethics Center.