Ultrasound Accuracy: Are Your Due Dates Reliable?

Question
how accurate do you think my ultrasounds could be i have had 3 ultra sounds now i had 1 at 7 weeks 5days anouther at 12 weeks 3 days and anouther at 21 weeks and 6 days they are all exact from each other i have been given the exact same due date each time and the exact same age of the fuetus which shows i conceived on 1 particular day do you possibly think that it could be wrong?  

Answer
An ultrasound can't be exact with the due date.  The date they give will have an error of 1 week or more.  That means the day of conception will be plus or minus 1 week.  It is very unusual that you would have 3 ultrasounds that would give the same due date.  The earliest ultrasound is the most accurate.  So I think your due date is very accurate, within 1 week.  That doesn't mean the baby will come on that date.  Babies usually come within 2 weeks of a due date, before or after.