Luke 2:5

To be taxed with Mary his espoused wife, being great with child.

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

to enrol himself with Mary, who was betrothed to him, being great with child.

to enroll himself with Mary his betrothed wife, being with child.

He went there to register with Mary, who was pledged to him in marriage and was expecting a child.