Of course many Catholic thinkers hold that view, and others see it differently. But as to the statement, "The Church teaches..."  I have looked, and so far been unable to find a magisterial statement that the soul comes at any particular point. If there was, I'd think it would be in the catechism, frequently cited and easily found, given current disputes. But it doesn't seem to be there, or elsewhere. Absent such a statement, it is available to think otherwise, and the Church's arguments against abortion treat the possible absence of a soul as immaterial. As always, I crave correction on factual matters -- just let me know where to look.