GRose is right...the best thing to do is stick with the original due date. The further along you get, the less accurate the EDD based on ultrasound is. For example, when I was pg with my son, I was about 7 months along, and the ultrasound said I was a full six weeks further along than I really was. I knew it wasn't possible, because I had ONE conception date to choose from for several months...lol. And this time, my "real" due date is 08/05/09.