Exegesis:

apograpsasthai sun Mariam tē emnēsteumenē autō ‘to have himself registered with Mary who was betrothed to him’; apograpsasthai depends upon anebē and the aorist tense refers to the specific act of Joseph’s registering as contrasted with the present tense in v. 1 and v. 3, referring to the registering of ‘the whole world’ and of ‘everyone.’

sun Mariam ‘with Mary,’ goes either with apograpsasthai (Revised Standard Version) or with anebē (New English Bible), preferably the latter.

ousē egkuō ‘being pregnant,’ a second apposition to Mariam, best taken as preparing for the subsequent verse which describes the birth of Mary’s child, the main objective of the whole narrative. But this should not be overstressed by making it the opening phrase of the next verses, cf. on v. 6.

egkuos ‘pregnant.’

Translation:

To be enrolled is separated by several phrases from its immediate constituent “went up”. Where this would be confusing or unidiomatic, one may have to change the word order, bringing the two verbs closer together in v. 4, e.g. ‘he went up to have himself registered, (going) from…,’ cf. “he travelled up for this purpose from…” (The Four Gospels – a New Translation), or to make v. 5 into a separate clause or sentence, repeating the reference to the journey, e.g. ‘he went up there (or, he did so) in order to have himself enrolled.’

With Mary. To make it clear that this phrase goes with ‘went up’ (see Exegesis) one may have to change the word order again, cf. ‘he went up with M., …, in order to be enrolled’ (Thai), or to render the phrase as a clause or sentence, e.g. “and he took with him Mary” (The Four Gospels – a New Translation).

His betrothed, who was with child, two qualifications, both going with “Mary”, the former mentioning a fact already known to the reader, the latter giving new information. Where both would have to be rendered as relative clauses it may be preferable to make the second one into an independent sentence, cf. ‘Mary who was betrothed to him. She was pregnant.’ For his betrothed see on 1.27. — Who was with child, or, ‘was pregnant.’ Often the rendering differs from that of ‘to conceive’ (1.24) only by its being without indication of the ingressive aspect, cf. ‘to be pregnant’ with ‘to become pregnant’ (Dutch versions), or ‘to be with belly’ with ‘to receive belly’ (Sranan Tongo).

Quoted with permission from Reiling, J. and Swellengrebel, J.L. A Handbook on the Gospel of Luke. (UBS Handbook Series). New York: UBS, 1971. For this and other handbooks for translators see here . Make sure to also consult the Handbook on the Gospel of Mark for parallel or similar verses.