At this time, the fetus is a little larger and easier to measure. Even dating scans can be inaccurate for the due date, but they are never as inaccurate as using the menstrual period. For instance a dating scan done at 6 weeks could get the date wrong five days either way.
Are pregnancy dating ultrasounds 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.
Can scan dates be wrong pregnancy?
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.
How often are pregnancy due dates wrong?
Its the same in most developed countries. But data from the Perinatal Institute, a non-profit organisation, shows that an estimated date of delivery is rarely accurate - in fact, a baby is born on its predicted due date just 4% of the time.