The earlier the ultrasound is done, the more accurate it is at estimating the babys due date. Ultrasounds performed during the first 12 weeks of pregnancy are generally within 3 - 5 days of accuracy. The most accurate time is between 8 and 11 weeks gestation.

Can early pregnancy scan dates be wrong?

It is very common when scanning an early pregnancy to find that the due date does not match the menstrual history. Sometimes the dates can be more than a week off and sometimes even as much as 4 weeks.