What is a dating ultrasound
The GS is not identifiable until approximately 4 1/2 weeks with a transvaginal scan.
Gestational sac size should be determined by measuring the mean of three diameters.
The CRL is a reproducible and accurate method for measuring and dating a fetus.
Early ultrasonographers used this term (CRL) because early fetuses also adopted the sitting in the chair posture in early pregnancy.
Sometimes there is difficulty distinguishing between the maternal pulse and fetal heart beat.
The Crown Rump Length (CRL) measurement in a 6 week gestation.
It is easier to determine chorionicity earlier in the pregnancy depending on the chorionicity and amnionicity.
It is a sad situation when a "vanishing twin" occurs, which is about 20% of twin pregnancies.
A mass of fetal cells, separate from the yolk sac, first becomes apparent on transvaginal ultrasound just after the 6th week of gestation. The fetal pole grows at a rate of about 1 mm a day, starting at the 6th week of gestational age.
Thus, a simple way to "date" an early pregnancy is to add the length of the fetus (in mm) to 6 weeks.