Exegesis:

egeneto de marks the approach of the climax of a narrative, cf. on 1.8.

en tō einai autous ekei ‘during their being there’; for the construction cf. on 1.8.

eplēsthēsan hai hēmerai tou tekein autēn ‘the days of her giving-birth (i.e. for her to give birth) were fulfilled,’ cf. on 1.23; eplēsthēsan continues the sentence introduced by egeneto.

Translation:

They, i.e. the two of them, which is made explicit where a dual form is obligatory, but also in some other languages, e.g. ‘the two’ (Malay, Toraja-Sa’dan), ‘they two together’ (Thai).

The time came for her to be delivered, see on 1.57.

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.