Pace the apologetic for keeping the question of “Prenatal Adoption” open, the text of the CDF’s Dignitas Personae hews to the reasoning that forbids contraception and IVF as well as the inviolability of the life of the embryo. Inviolability of human life is the easiest reason to understand, while the most difficult is the inseparability of love and life that engenders it – the relational ontological of the human person imaging the divine Persons. This works within a distinct and higher experience, but is the most ontological, profound and realist.
This is the touch-stone of the question. Embryos cannot be inserted into the uterus of an “adopting” mother because the child will not be present as the result of an act of love, but of an act of technology. If I may assert it this way, the act of love that is life-giving trumps as moral criterion the saving of the life. Cf. #19 of DP
 Arland K. Nichols, “Prenatal Adoption: Did the CDF Close the Door on Debate?” Fellowship of Catholic Scholars Quarterly. Number 4, Winter 2011, 26-30. Nichols says no. On my reading, the answer is yes.