Luke 2:3-6

So everyone went to be registered, each to his own town. And Joseph also went up from the town of Nazareth in Galilee, to Judea, to the city of David, which is called Bethlehem, because he was of the house and family line of David, to be registered along with Mary, who was engaged to him and was pregnant. While they were there, the time came for her to give birth.