When people ask me how many months, i tell them how mnay months (or in my case now, weeks) I have left till bub is due... So bub is due in 2 weeks for me (mid march).... but back in say mid December, I would have called myself 6 months pregnant, and told people the baby is due in 3 months.... People dont understand the number of weeks thing, i find.
I think of a month as a calender month, rather than 4 weeks...