Its funny that you posted this thread because I was just thinking about the accuracy of scan today. I was digging through the medical history I brought from the U.S. for my pregnancy file from last time and I realised how off they were. I had the same problem as you- I never had periods. In fact I'd be lucky to get them twice a year so we had no idea how pregnant I was. They did an internal scan and told us our due date was Jan 28 (of 2003). Then when I had my N/T scan at 12 weeks they readjusted because the ultrasound showed the baby was almost 2 weeks younger so my due date became Feb 9 instead. As it turns out they ended up inducing me on Jan. 27th because the amniotic fluid was low and the baby had stopped growing. Carter was fine of course but if you ask me not everyone is the same and even though they say that a scan in the early weeks is almost 100 percent accurate obviously with me it wasn't. In pregnancy because its such a long wait for such a wonderful event we tend to want to know EVERYTHING! In the end though your baby is born and everything is wonderful.