Let's say the first few weeks of pregnancy you were told a certain due date and a conception date based on that. Now don't they base alot of that on when the mother says her last period was? I mean, if the mother gave incorrect information, couldn't that affect the dates? I know ultrasound, hormone levels, etc. also play into setting a date....but I know those can sometimes be misleading depending on alot of things.

My question is this.....if a doctor a few months in moves the due date up from where it was originally.....does that mean that technically the conception date also had to be earlier than first thought? I know conception dates are hard to exactly pinpoint at any point in a pregnancy, but is it at least possible?

I was with a girl when she got pregnant the first time we had sex, which was 5 days after we started dating. I have been told the original due date possibly has been moved up now.....I am not sure how much. However, if the new due date is a week or 10 days earlier than first thought, wouldn't that put the conception date 7-10 days earlier, too, or before I even knew her......meaning it very well may be someone else's baby?