Matthew 1:18, completed!

So far we have:

Mνηστευθείσης της μητρός αυτού Μαρίας τῳ Ιωσήφ,
(After/when) his mother Mary was betrothed to Joseph

πριν ή συνελθείν αυτούς
before they got married

ευρέθη εν γαστρί έχουσα εκ πνεύματος αγίου.

The first word, 'ευρέθη' is an aorist passive form of the verb 'ευρίσκω', meaning generally, 'find'.
Since it's in the passive form, we can translate it as 'was found'. Who or what was found? - Mary.

Then we have an idiom: 'εν γαστρί έχουσα'. Literally this means, 'in belly/womb having', but the idiomatic meaning is 'pregnant'.

So before they got married, Mary was found (to be) pregnant. Notice that the literal meaning of these first four words, in the same order, would not make an easily readable phrase in English:

ευρέθη εν γαστρί έχουσα
was found in womb having
(was found to be pregnant)

But the kicker is at the end of the verse. Mary was found to be pregnant

εκ πνεύματος αγίου
out of spirit holy

The adjective 'άγιος' means 'holy', and 'πνεύματος' is the genitive singular form of the word 'πνεύμα', which has various meanings centered around 'breath' or 'wind', but here is translated 'spirit' (in older terminology, 'ghost'). (See www.greekbiblestudy.org and left-click on 'πνεύματος' in Matthew 1:18. Then choose 'short definition' or 'long definition' for more information about this word.)

The word 'εκ' is a preposition taking the genitive case; it means 'out of'.

So we have

εκ πνεύματος αγίου
out of (the) holy spirit

The article ('the') is typically added in English translations; it is not present in the Greek, which literally reads 'out of a spirit holy'.

So one genitive absolute, one use of the accusative as subject of an infinitive, two participles, and a couple more verbs later, and we're done! Altogether we read:

Του δε Ιησού Χριστού η γένεσις ούτως ην.
And the birth of Jesus the Messiah was thus -

Mνηστευθείσης της μητρός αυτού Μαρίας τῳ Ιωσήφ,
After his mother was betrothed to Joseph

πριν ή συνελθείν αυτούς
before they were married

ευρέθη εν γαστρί έχουσα
she was found to be pregnant

εκ πνεύματος αγίου.
out of (by) the holy spirit.

One verse, a lot of grammar. Χαίρετε!