{To enrol himself with Mary} (apograpsasthai sun Mariam).
Direct middle. "With Mary" is naturally taken with the infinitive
as here. If so, that means that Mary's family register was in
Bethlehem also and that she also belonged to the house of David.
It is possible to connect "with Mary" far back with "went up"
(aneb(885c)) in verse  4 , but it is unnatural to do so. There is no
real reason for doubting that Mary herself was a descendant of
David and that is the obvious way to understand Luke's genealogy
of Jesus in  Lu 3:23-38 ). The Syriac Sinaitic expressly says
that both Joseph and Mary were of the house and city of David.
{Betrothed} (emn(8873)teumen(886e)). Same verb as in  1:27 , but here
it really means "married" or "espoused" as  Mt 1:24f.  shows.
Otherwise she could not have travelled with Joseph. {Great with
child} (enku(9369)). Only here in N.T. Common Greek word.