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 ultrasounds be off by a few days?

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.

Is two weeks too early for an ultrasound?

Most practitioners wait until at least 6 weeks to perform the first pregnancy ultrasound. However, a gestational sac can be seen as early as 4 1/2 weeks after your last period, and a fetal heartbeat can be detected at 5 to 6 weeks (though that isnt always the case).

What is the percentage of an ultrasound being wrong?

The chances of an error with ultrasound are up to 5 percent, says Schaffir. An ultrasound can be between 95 to 99 percent accurate in determining sex, depending on when its done, how skilled the sonographer is and whether baby is in a position that shows the area between their legs. Mistakes can also be made.