I heard that sometimes if your uterus is enlarged enough, it can make the doctor suspect that you are. In which case they usually ask you to do a pregnancy test.
But I'm not completely sure on that.
From what I have read and experienced personally...yes. Your cervix and uterus change shape and colour. For both of my pregnancies my Dr could tell I was pregnant during the pap. He said everything looks as it should for being pregnant and that was when I was only 4 weeks gestation.