Wouldn't it be a tiny bit inaccurate to translate this as She's seven months pregnant ? I mean, her seventh month might have only just started, and you could still use the Swedish sentence, but you can't say that she's 7 months pregnant, because she could be, say six months and one day pregnant but still technically in her seventh month.
That said, I'm sure those are just trivialities :)
You leave out the den and you don't replace for nothing? I have problems with that, I have a bad habit of insisting that when we translate something must have each word corresponding from the previous sentence. "i sjunde" is simply "in the seventh "? How will I know when put "the"