The results showed that in over 50% of cases the estimated date of delivery derived from the ultrasound scan was more accurate than that derived from the last menstrual period, whatever the discrepancy between the two predictions.

Is scan due date always accurate?

How accurate is the ultrasound examination? 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.