I don't think the pregnancy was rushed. She revealed to him that she was pregnant when he returned after saving the Chancellor. But they also both said it had been a long time since they had been together and that it would have been even longer if he hadn't gone on this mission to save Palpatine. So, obviously, the conception happened during their last meeting which could have been any amount of time prior up to nine months taking into consideration that humans in this galaxy far, far away have a nine-month pregnancy term. Who really knows. She was showing when they met up by the landing platform.