Evidence suggests that ultrasounds more accurately predict your due date than using your last menstrual period—but only in the first trimester and early second trimester (until roughly 20 weeks). 3 Early ultrasound due dates have a margin of error of roughly 1.2 weeks.

How accurate is ultrasound dating of fetus?

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.