Purely from a Gospel perspective, the Virgin birth is given credence as when the Angel Gabriel announces to her that she is to become the mother of a child she asks, "How can this be, seeing I have no husband?"
She later consents, "Behold the handmaid of The Lord. Be it unto me according to thy will." Both quotes from St Luke.
St Matthew says, " Now when Joseph discovered that she was with child he was minded to put her away privily," suggesting that he was not responsible for the pregnancy.