What is a dating ultrasound
This is the result of normal midgut proliferation and will resolve by 11 weeks as the fetus lengthens.This physiological occurrence should not be confused with an omphalocele.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.For more details go to the following link: The Fetal Medicine Foundation.Initially twins may be identified as 2 separate gestational sacs (ie diamniotic, dichorionic) They may be 2 fetal poles within the same gestational sac (monochorionic).These differences rarely effect gestational age dating by more than a day or two.
The Crown Rump Length (CRL) measurement in a 6 week gestation.
Failure to identify (with transvaginal ultrasound) a yolk sac when the gestational sac has grown to 12 mm is also usually indicative of a failed pregnancy.
Using a transvaginal approach the fetal heart beat can be seen flickering before the fetal pole is even identified. It may be below 100 beats per minute but this will increase to between 120- 180 beats per minute by 7 weeks.
The gestational sac(GS) is the earliest sonographic finding in pregnancy.
It will be difficult to see if the mother has a retroverted uterus or fibroids.