From Instruction on Respect for Human Life in Its Origin and on the Dignity of Procreation Replies to Certain Questions of the Day (Donum Vitae).
February 22, 1987, Congregation for the Doctrine of the Faith
5.I.1. What respect is due to the human embryo, taking into account his nature and identity?
The human being must be respected – as a person – from the very first moment of his existence.
Thus the fruit of human generation, from the first moment of its existence, that is to say from the moment the zygote has formed, demands the unconditional respect that is morally due to the human being in his bodily and spiritual totality.