5 in order to be registred with Mary, his espoused wife, who was then big with child.
Luke 2:5 Cross References - Mace
Matthew 1:18-19
18 Now the manner of Christ's birth was this: his mother Mary being promised in marriage to Joseph, before they came together, she became pregnant by the holy Spirit.
19 but Joseph her husband, being a good-natur'd man, and unwilling to expose her to publick shame, he designed to put her away privately.