In Luke 1:26-38 the angel Gabriel comes to Mary and announces to her that she has found favor with God and that she will become pregnant with the Son of God. Mary does not understand how this could be as she was virgin and asks the angel to explain how this could happen. Gabriel tells her that The Holy Spirit will come upon you and the power of the Highest will overshadow you and that Holy One who is to be born will be called the Son of God. He also said that with God, nothing is impossible! Her response was,  "Behold, the bondslave of the Lord; be it done to me according to your word."

The angel answered, "The Holy Spirit will come upon you, and the power of the Most High will overshadow you. So the holy one to be born will be called the Son of God.

We, at salvation, are all impregnated with the Word of God - Jesus - by The Holy Spirit. As the baby Jesus began to take over Mary's body and told her when to lay down; when to sit down; when and what to eat; how to walk (when you are pregnant with the Word, you begin to walk funny - at least those who are not pregnant think so!), He was preparing her for her future - to give birth to the Word of God!