Re: How off could my due date be based on early utrasound? I know it's wrong.
Well, babies grow at such different rates later in pregnancy (hence why you have a 7 lb baby and I have a 10 lb baby at 40 weeks, for instance) that I don't think a later u/s is going to be more reliable. Statistically, early u/s is just more accurate for dating--though it can definitely be off.
This may ultimately be an unresolvable mystery--all these tools are just going to yield good estimates (some better than others). Even LMP is just going to give you an estimate.
Maybe your best bet is to talk to your doctor about what the consequences might be if you go into labor at a certain point and see if you can come to some compromise about how you and your doctor will handle the birth, depending on when you go into labor.
Catherine, mama to Preschooler Girl 9/08, Toddler Boy 3/11, and Twin Girls 2/14!