Mormon Doctrine, pg. 822; “Our Lord is the only mortal person ever born to a virgin, because he is the only person who ever had an immortal Father. Mary, his mother, “was carried away in the Spirit” (1 Ne. 11:13-21), was “overshadowed” by the Holy Ghost, and the conception which took place “by the power of the Holy Ghost” resulted in the bringing forth of the literal and personal Son of God the Father. (Alma 7:10; 2 Ne. 17:14; Isa. 7:14; Matt. 1:18-25; Luke 1:26-38.) Christ is not the Son of the Holy Ghost, but of the Father.”
Luke 1:26-28; “And in the sixth month the angel Gabriel was sent from God unto a city of Galilee, named Nazareth, 27 To a virgin espoused to a man whose name was Joseph, of the house of David; and the virgin’s name was Mary. 28 And the angel came in unto her, and said, Hail, thou that art highly favoured, the Lord is with thee: blessed art thou among women.” (See entire passage Luke 1:26-56)
Contrary to popular Mormon belief, God did not have sex with Mary.