Are Due Dates Miscalculated?

As pregnancy progresses, the accuracy of an ultrasound for predicting due dates decreases. Between 18 and 28 weeks of gestation, the margin of error increases to plus or minus two weeks. After 28 weeks, the ultrasound may be off by three weeks or more in predicting a due date.

Can your due date be wrong?

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 accurate are birth due dates?

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.