To be taxed with Mary his espoused wife, being great with child.
Berean Study Bible (BSB) - Luke 2:5 >He went there to register with Mary, who was pledged to him in marriage and was expecting a child.
Textus Receptus (TR) - Luke 2:5 >ἀπογράψασθαι σὺν Μαριὰμ τῇ μεμνηστευμένῃ αὐτῷ γυναικί, οὔσῃ ἐγκύῳ.