It has been reported that approximately one half of women accurately recall their LMP 2 3 4. In one study, 40% of the women randomized to receive first-trimester ultrasonography had their EDD adjusted because of a discrepancy of more than 5 days between ultrasound dating and LMP dating 5.

Is dating scan or LMP more accurate?

The study found that the earlier the ultrasound assessment in pregnancy (preferably between 10 and 12 weeks), the more accurate the prediction of date of birth. The results indicate that after 24 weeks of pregnancy, a reliable LMP last menstrual period provides better estimates.

Is dating pregnancy from last period accurate?

An ultrasound is actually the most accurate way to date a pregnancy because all fetuses grow at a consistent rate during the first trimester and early second. In other words, if your baby measures 9 weeks 2 days when you have your ultrasound, thats how far along you are, no matter when your last period was.

Why do LMP and ultrasound dates not match?

LMP versus early ultrasound If the ultrasound date is within seven days of your LMP date, we would stick with your LMP date. Ultrasounds done later in the pregnancy are less accurate for dating, so if your due date is set in the first trimester, it shouldnt be changed.

Can scan lie about weeks of pregnancy?

Ultrasounds performed after 22 weeks gestation cannot be used to estimate the due date of the baby because the size no longer reflects the age very well. Even average babies can differ by up to 2 to 3 weeks of growth;. These scans are only used to estimate the due date of your baby if this is all you have to go on.