That's funny... in my first trimester especially, I was having a lot of X-rated dreams about OTHER men! It was really alarming, as I honestly have no desire to be with anyone else, but you can't help your dreams I guess.
DH told me that he once read that when women get pregnant sometimes a biological drive kicks in that makes them want to be promiscuous... nature's logic being that if the woman is with a few different men, all of these men will think it's their child so the baby will be better protected. I'm not sure WHERE he read that as I'd never heard it before, but then when my dreams started I wondered if there was something to it. (No, I never told him about my dreams. I'm always accusing him of dream-cheating on me, so I can't fess up myself!)