This suggests that in general ultrasound dating is more accurate in predicting the birth date than counting from the last monthly period1,2 but it is still only an estimate and may not always be accurate.

Is dating scan more accurate than LMP?

A dating scan is more accurate. If the scan date differs from your last period dates, the scan date will be used. The scan will usually show that your pregnancy is less far along than suggested by your LMP.

Can ultrasound scan dates be wrong?

3 Early ultrasound due dates have a margin of error of roughly 1.2 weeks. After 20 weeks of pregnancy, your estimated due date shouldnt change based on an ultrasound because it will be less accurate. And remember: Its an estimated due date; the vast majority of women dont deliver their babies the day theyre due.

How accurate are ultrasound dating scans?

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.