Embryo measurements dating
It should be noted that errors of about 10% are reported and that even at this level of accuracy it is disappointing.It is suggested that there may be an improvement in accuracy of about 5% in using three rather than two parameters.
Gestational Sac: The first element to be measurable is the gestation sac of the early pregnancy.
The abdominal circumference is measured at the level of the liver and stomach, including the left portal vein at the umbilical region.
If we assume a fetus is growing normally, biometric measurements are determined by gestational age, and we can estimate the gestational age and thus the due date.
The gestational sac is measured in three dimensions, and the average, the Mean Sac Diameter (MSD) used for estimating gestational age.
It is useful between 5 and 8 menstrual weeks with accuracy of /- 3 days .