Exegesis:

pōs estai touto lit. ‘how will this be’; touto refers to what is announced in v. 31, and the clause expresses Mary’s astonishment, rather than curiosity or unbelief.

pōs ‘how,’ inquires after the way in which something happens, but also after the possibility as in 20.41, 44; Jn. 12.34; hence the translation ‘how can this be?’

epei andra ou ginōskō ‘since I have no sexual relationship with a man’; andra means ‘any man’ including Joseph. The phrase does not refer to marriage (cf. on v. 27). The present tense implies that Mary expects the angel’s prophecy to be fulfilled shortly. ginōskō denoting sexual intercourse is Hebrew usage, cf. e.g. Gen. 4.1, 17.

epei ‘because,’ ‘since.’

Translation:

How can this be, or, ‘how will this be possible’ (Bible en français courant), or “how will this be brought about” (The Four Gospels – a New Translation), or more explicitly, ‘how can I become pregnant’ (Cuyono).

I have no husband, lit. ‘I do not know a man.’ In several other languages besides Hebrew and Greek the verb ‘to know’ can be used with reference to sexual intercourse (or especially to the first intercourse a person has), e.g. in Marathi, Sranan Tongo, Balinese, Uab Meto, Mossi , where necessary slightly adjusting the clause, e.g. ‘there is no man that knows my body’ (Tae’). In the many languages, however, where ‘to know’ cannot have this metaphorical meaning, another current expression for cohabitation must be used, which should be clear without being vulgar, cf. “I have not lain with any man” (The Four Gospels – a New Translation), “I am a virgin” (Good News Translation), ‘I live with no man’ (Bolivian, Quechua), the dual form of the verb ‘to stay/be-present’ (Ekari), ‘I have not been/joined with a man’ (Kituba, Thai). In some languages a speaker has to use a specific negative particle when he knows, or supposes, that the event he is denying for the present will happen in the future. As it is normal for a betrothed girl to suppose sexual relationship in the future, several versions use ‘not-yet’ here, e.g. Apache, Navajo, Tboli, Sranan Tongo, Bahasa Indonesia, Balinese, also Thai, Kituba (see above). To demonstrate the importance of this point Navajo may be cited, in which language the rendering ‘my-husband yet being-lacking’ conveys the intended meaning, whereas without ‘yet’ the phrase would suggest either, ‘I have no husband,’ or, ‘my husband is not here just now,’ or, ‘my husband is dead.’

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.