How accurate is the early pregnancy scan dating? The dating is most accurate when the scan is performed between 7-11 weeks. The Estimated Date of Delivery (EDD) is accurate to within 3 days and is calculated from measuring the length of the embryo (Crown Rump Length).

Is dating ultrasound 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.