Reliability of ultrasound dating
The EDD from the early dating scan is used - if the last menstrual period is not known or is unreliable, or the dating scan differs from the last menstrual period dating by more than 5 days.
As the baby gets bigger, it starts to express its individual growth potential.
These scans are only used to estimate the due date of your baby if this is all you have to go on.
For example if you a tiny sac can be seen in the uterus, but the baby and its heart beat may not be detected yet.In spite of this ongoing debate as to the feasibility and efficacy of routine ultrasound evaluation in pregnancy, one thing remains clear: ultrasound examination of the fetus provides the most precise assessment of gestational age, especially in the first trimester.This variance has evolved from years of study by several esteemed researchers who have sought the most accurate measurement parameters in determining gestational age and normal patterns of fetal growth.Sometimes a trans-vaginal examination shows that your pregnancy is less advanced than expected.The earlier the ultrasound is done, the more accurate it is at estimating the baby's due date.