Mary was over shadowed by the Spirit of God and became "with child." The assumption has been that God's Spirit caused the child to form in Mary. Since God created humans to have a birth mother and a birth father, I would assume that Mary being the birth mother was fully a birth mother in that her egg was used and her blood flowed through the newly formed child - Jesus.
Not knowing the mind of God on this, and I don't believe I have ever heard a discussion on the place of Mary's egg in the birth of the Son of God as Son of Man, I don't believe we can say that we know for a certainty how Jesus was actually formed inside his birth mother, Mary.