B'Elanna's was about 3/4 of a season, or 9 months to you and me. But that was 'Voyager'.
K'Ehleyr (Alexander's mum) must have had a much shorter pregnancy, and one of the Duras sisters was pregnant too, but I don't remember much about it. The episode where Worf meets a future Alexander would tell me, IIRC.
I think Stripe is going to give us an answer shorter than 3/4 of a season.