There seem to be some misconceptions about the Annunciation. It is said that she became pregnant with the Incarnate Word before marriage; school children are even taught that she wasn't sure if she could look after a baby.
Yes, the Archangel Gabriel descended from Heaven in corporeal form, with a multitude of blessed spirits to make the announcement to the Blessed Virgin Mary. It is also written in The Divine Life of the Most Holy Virgin which was communicated by the Blessed Virgin herself to the Venerable Mary of Agreda (whose body remains incorrupted in Agreda, Spain, for the last four hundred years and the Catholic Church is working on canonizing), that she was fourteen years, six months and seventeen days old. She had also been married for six months, having been espoused to St. Joseph on her fourteenth birthday.
She was completely absorbed in contemplation of the mysteries she had learnt and been shown over the previous nine days regarding all of Creation with its minute details and of her transportations both body and soul into Heaven. She earnestly wished to serve the woman who would become the Mother of the Messias. The Archangel Gabriel entered her chamber with the many spirits, bowed and gave homage to the Blessed Virgin; not the other way round as is often depicted in images of the Annunciation, where she is kneeling or the Archangel is hovering above her.
As we know, the Archangel Gabriel saluted her with the words, 'Ave Maria! Gratia plena!' - Hail Mary, full of grace! She was troubled as she believed herself to be the least of all creatures and had doubts on how she could become a mother and preserve her chastity at the same time. The Archangel explained how this would occur and she humbly gave her consent, 'Ecce ancilla Domini; fiat mihi secundum verbum tuum' - Behold the handmaid of the Lord; be it done unto me according to Thy word.
At that moment, her chaste heart distilled three drops of blood which fell into her virginal womb. From these, the Holy Spirit formed the Body of Our Lord and in the same instant, his most holy Soul was created and infused into his Body.
As we celebrate the Annunciation on May 25, let us remember how it really happened.
Fr. Bonaventure Amedeo de Caesarea, M.C. 1997. The Divine Life of the Most Holy Virgin. (An abridgement of the Mystical City of God by Ven. Mary of Agreda). Tan Books and Publishers, Rockford, Illinois, pp 42-53.