Just received a new job

Hey everyone I just received a new job and go in tomorrow to fill out the hire paperwork. I am currently 23 weeks pregnant and am showing but at my interview I had a loose shirt on so it was a little harder to tell so I am not sure if the guy who hired me noticed or not but I was still hired that same day. I thought it would be weird to say oh and by the way I am pregnant. My boyfriend told me that I should have said something but why should I? Would it matter if I didn't say anything and he notices tomorrow when I go in to fill out my paperwork? I already put in my two weeks at my current job so I could take this new job. At the interview he said that his employees stay busy and are on their feet. I don't know what to do. Can he change his mind about hiring me once he notices? I am really nervous and don't know what to do.