Dogma says that an angel or the holy spirit visited her. My guess was that the sperm came either from bath water (Joseph washed first then Mary) or a Roman soldier (we know how that could happen, right?).
Different religions groups have different beliefs about this topic; there are basically two explanations: (1) A miracle, as mentioned in The Bible; (2) That she actually got pregnant from a man (pressumably her husband).
Roman Catholic Answer
from The Catechism of the Catholic Church, second edition, English translation 1994
Conceived by the Power of the Holy Spirit
484 The Annunciation to Mary inaugurates "the fullness of time," (Gal 4:4) the time of the fulfillment of God's promises and preparations. Mary was invited to conceive him in whom the "whole fullness of deity" would dwell "bodily." (Col2:9) The divine response to her question, "How can this be, since I know not man?" was given by the power of the Spirit: "the Holy Spirit will come upon you." (Lk 1:34-35)
485 The mission of the Holy Spirit is always conjoined and ordered to that of the Son. (Cf. Jn 16:14-15) The Holy Spirit, "the Lord, the giver of Life," is sent to sanctify the womb of the Virgin Mary and divinely fecundate it, causing her to conceive the eternal Son of the Father in a humanity drawn from her own.
485 The Father's only Son, conceived as man in the womb of the Virgin Mary, is "Christ," that is to say, anointed by the Holy Spirt, from the beginning of his human existence, though the manifestation of this fact takes place only progressively: to the shepherds, to the magi, to John the Baptist, to the disciples. (Cf. Mt 1:20; 2:1-12; Lk 1:35; 2:8-20; Jn 1:31-34; 2:11) Thus the whole life of Jesus Christ will make manifest "how God anointed Jesus of Nazareth with the Holy Spirit and with power." (Acts 10:38)
From the Gospel of St. Luke 1:35: The angel answered, 'The Holy Spirit will come upon you, and the power of the Most High will cover you with its shadow. And so the child will be holy and will be called Son of God.' This is from the King James Version.
According to the Christian traditions, the Holy Spirit comes to Mary and impregnates her. Most churches try to ignore the physical and biological method of sperm and egg, but usually Jesus is considered to be biologically a descendant of Mary. He is of her or the fruit of her womb. Thus she provided the egg and the Holy Spirit provides the necessary divine power to duplicate the action of a sperm cell.
According to Islam (in the Qur'an), God (Allah) merely wills that she is with child and through his Divine grace/power the child come to existence inside of here.
Mary gave birth to Jesus in Bethlehem, like all other babies are born. But the day and date are not certain.
Mary gave birth to Jesus as she conceived by the holy ghost.
She got pregnant through the holy spirit, though in a biological sense it's not really clear on what happened exactly. *Immaculate Conception
She was made pregnant by the power of the Holy Spirit.
Through the miracle of the Holy Spirit
According to Christian belief, Mary conceived Jesus through the Holy Spirit, not through intercourse with Joseph. This event is known as the Virgin Birth.
Mary is the mother of Jesus, Elizabeth is the mother of John the Baptist.
Some special times in Mary's life include her Annunciation, when she was told by the angel Gabriel that she would conceive Jesus; the Nativity, when Jesus was born; the Presentation of Jesus at the temple; the Wedding at Cana, where she asked Jesus to perform his first miracle; and her presence at the foot of the cross during Jesus' crucifixion.
Mary is a central figure in the Christmas story as she is the mother of Jesus. According to Christian tradition, she was visited by an angel who told her she would conceive Jesus by the Holy Spirit. Mary's faith and obedience to God's plan make her a symbol of humility and devotion in the story of Jesus' birth.
Mary was Jesus' mother.
The Annunciation mysteries refer to the event in Christian belief when the archangel Gabriel announced to the Virgin Mary that she would conceive and give birth to Jesus. These are part of the Joyful Mysteries of the Rosary and are focused on reflecting on the incarnation of Jesus.
That's why it was called a "miracle".
God was not married to Mary, the conception of Jesus Christ was not like it is for us humans, no physical contact ensued. It was an act of the Holy Spirit and happened supernaturally. For GOD nothing is impossible!
Mary is the mother of Jesus
Joeseph Answer. Joseph would have been the obvious choice as there are few who believe in the miraculous birth of Jesus. If one does then the father of Jesus would have had to have been God. It is not beyond the capability of God to plant a seed into Mary so that she would conceive. How this was done is beyond our comprehension.
The young Jewish girl Mary, betrothed to Joseph, when told she would please God to conceive the child named Jesus who would be called the Son of God, replied, "Let it be done unto me according to your word." MARY!!
At the crucifixion of Jesus, Mary, the mother of Jesus, was present along with Mary Magdalene and Mary the wife of Clopas. They stood by the cross and witnessed Jesus' suffering.