I believe that one of the central scriptures to this point is Jeremiah !:5
Before I formed you in the womb I knew you, and before you were born I consecrated you.
I think this is pretty explicit that the material is blessed before birth (consecration is uniting material to spiritual gift). However it also leads me to believe that the soul existed before the material.... I believe the most widely accepted theological theory, immediate ensoulment, presupposes the soul to be invested when sperm and egg unite because that is when it actively begins to develop by its 'own' power. I think a lot of this can be reasoned out by looking at end of life issues similar, where even missing several faculties the potential for humanity still exists.....
umm... immediate creation of the rational soul by God is a dogma
(immediate, not meaning necessarily at the fertilization of the egg, but that God directly creates the soul at the conception of the person, which is either at the same time or after fertilization)
And I would say, even missing several faculties, humanity, not its potential, still exists. Its potential would allow for killing that thing which is not human but only potentially so. Just as we do not call it murder when we kill eggs and sperm before fertilization at least.
That said, Jeremiah 1:5 is literally referring to Jeremiah. Traditionally, this is taken both with regard to his predestinated role, and to his being cleansed from original sin while in the womb. We need only look at a fuller context
And the word of the Lord came to me, saying: Before I formed thee in the bowels of thy mother, I knew thee: and before thou camest forth out of the womb, I sanctified thee, and made thee a prophet unto the nations.
I quote the DR for two reasons. One the thee and thou, meaning a singular, not a plural you. Jeremiah is being addressed personally. Second, the translation sanctified rather than consecrated. I don't know Hebrew that well, but it is singular there and the verb can mean sanctify or consecrate. In any case the "and made thee a prophet" clearly does not apply to all!