Like I said before, a miscarriage is unintentional. In ivf we know for sure that not all are going to stick. Intent is the key word. A rough analogy would be knowingly sending 5 people into a situation you created where only one or none survive (if you’re lucky, 2 or 3) vs a natural situation where one person might die depending on his/her luck, lol. For the former, we are certain that lives will be lost. In reference to IVF, they’re creating people who will die. For the latter, it’s not in our control and we didn’t create that situation. In reference to sex, we are not consciously ‘creating’ someone (ie we are not consciously fertilizing) and it’s all left to chance.
Kind of like how the Church allows medical treatments that the mother needs that may result in the death of her unborn kiddo, but a direct abortion would not be permitted.
But you know this already. Your root issue is that you don’t believe that the embryo has the same value as a born human??