Luke 2:3

Now in those days, a decree went out from Caesar Augustus that all the world should be enrolled.

This was the first enrollment made when Quirinius was governor of Syria.

Joseph also went up from Galilee, out of the city of Nazareth, into Judea, to David’s city, which is called Bethlehem, because he was of the house and family of David,

to enroll himself with Mary, who was pledged to be married to him as wife, being pregnant.

While they were there, the day had come for her to give birth.