Matthew 1:20,21 NLV ... As he (Joseph) considered this (the things he was told by the angel), the Lord appeared to him in a dream. "Joseph, son of David", the angel said, "do not be afraid to take Mary as your wife. For the Child within her was conceived by the Holy Spirit. She will have a Son and you are to name Him Jesus, for He will save His people from their sins."
In this Scripture, the angel is speaking to Joseph, the father of Jesus, telling him to change his plan of putting Mary away because she became pregnant ourside of their marriage. He thought that she'd been unfaithful to him. Gabriel, the angel set him straight, Joseph's mind was changed, and he went back to his original plan. He was not this Baby's father ... he and Mary didn't come together outside of their marriage to conceive the Child. The Holy Spirit was the Father of Jesus.
Matthew 1:22-25 NLV ... All of this occurred to fulfill the Lord's message through His prophet: "Look! A virgin will conceive a Child! She will give birth to a Son, and they will call Him Immanuel, meaning 'God is with us'." When Joseph woke up, he did as the angel of the Lord commanded and took Mary as his wife, but he did not have sexual relations with her until her Son was born. And Joseph named Him Jesus.
They didn't have any sexual union until after Jesus was born. You may think: "virgin birth ... that's impossible." The medical profession says: "No, it's not impossible ... but if it does happen, the baby will be female, not male."
This Scripture says that the Holy Spirit fathered Jesus, a male Child. So this had to be a supernatural happening.
Reverend Robert W. & Mary C. Butler