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

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

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

Darby Bible Translation
to be inscribed in the census roll with Mary who was betrothed to him [as his] wife, she being great with child.

Douay-Rheims Bible
To be enrolled with Mary his espoused wife, who was with child.

English Revised Version
to enroll himself with Mary, who was betrothed to him, being great with child.

Young's Literal Translation
to enrol himself with Mary his betrothed wife, being with child.