The Church has always maintained a position against abortion. This goes all the way back to one of the earliest non-Scriptural documents in the first-century document known as the
Didache:
“Thou shalt do no murder; thou shalt not commit adultery”; thou shalt not commit sodomy; thou shalt not commit fornication; thou shalt not steal; thou shalt not use magic; thou shalt not use philtres [love potion or aphrodisiac]; thou shalt not procure abortion, nor commit infanticide; “thou shalt not covet thy neighbor’s goods”;
No magisterial teaching has ever contradicted the immorality of abortion. No serious theological consensus has ever contradicted the immorality of abortion. The question has never been, “Is abortion evil?” but always, “How evil is abortion?” In other words, “Is abortion murder, or something less?” Popes never varied on the evil of abortion, but they made the penalty for abortion sometimes greater, sometimes less, based on their understandings of fetal ensoulment. This is perfectly normal Catholic teaching at work: while the
teachings remain the same, canonical
enforcement of them varies based on pastoral concerns and the Curia of the moment.
Aquinas is, as usual, the best exponent of high medieval Catholic thought. He concluded that the soul was not infused until quickening. Based on his understanding of pregnancy, there was no evidence of an animate force working within the foetus until the child “leapt in the womb”, as John in the womb of Elizabeth. Thus, it was at least possible that abortion was
not murder. The question was eventually settled not by advances in theology, but by advances in
medicine. Improved understanding of the process of pregnancy revealed that, in fact, the human creature is a separate, animate substance from the moment of union between sperm and egg. This proves it has a soul. That means abortion is murder, and there is not one great Catholic theologian or saint in the past two thousand years who would disagree, if they had access to the information we do. Their arguments that abortion was a lesser crime depended on a flawed understanding of human biology.
In any event, while our understanding of what abortion actually is has varied somewhat, our understanding that it is a serious evil has been continuous since the inception of Christianity. Although the question has been raised for legitimate inquiry at various points down the centuries, the Catholic Church has never at any time taught that direct abortion is ever acceptable, even if the life of the mother is in danger.
However – and this is a big however – the Church does maintain that life-saving medical procedures may be performed on the mother, even if those procedures are certain or all but certain to lead to the unintended death of the fetus. For example, a mother with cancer may take chemo therapy. A mother with an ectopic pregnancy may
not kill the child with poison or surgical abortion, but
may (and perhaps
must) have the fallopian tube removed before it kills her, even though it is
extremely unlikely that her child will survive the procedure. These are very grave circumstances, but they do arise, and life-saving procedures, with love of both mother and child in mind, are permitted.
Does that make sense?