I remember a while back there was "something" (I say something because it could have been fact but it could have been a rumor) going around that Nick wanted biological children and Jessica wanted to adopt. Well one could assume her logic behind that was not wanting to gain the weight and "ruin her body".
Again, who knows if this is true or not.
As for the pregnancy rumor, could be true, could be not. Remember when Tom and Nicole split up, it was all over the news and then like a month later Nicole miscarried. And that was all over the news. If she hadn't miscarried, she would have announced she was pregnant after the split.