"Abortion where allowing the pregnancy to proceed puts the mother at risk of serious harm or death, and no medical alternative exists, then abortion becomes a special case of self-defense, and almost nobody denies that the taking of another human life, which abortion does, is justified in that case"
This is not Catholic teaching. Active abortion is always wrong. The loss of a child as a side-effect of treatment received by the mother is not abortion, though, because the death of the child is not the intention. Hundreds of doctors have repeatedly certified that there are no medical conditions that require active abortion to save the life of the mother. Look it up.