Is ultrasonography of any attraction contained by assessing pregnancy during the third week?what structures common?

yes. but there is no human resembling structure yet.3 weeks embryo is just about 1/12"long,the size of a pencil point. It most closely resembles a worm, long thin next to a segmented end.
Please see the webpages for more details on Pregancy ultrasound and Ultrasonography.
Week 1-4 After conception, the embryo will inaugurate to "search" for a place to attach to the woman's uterus. When it finds one and plants itself there, the connections between the woman and the embryo will set off to form, including the umbilical cord.
Scans may be performed within the first trimester (a period of three months) to:
Confirm a everyday pregnancy
Assess the baby's age
Rule out abnormalities, such as ectopic pregnancies or potential for miscarriage
Assess the baby's heart
See if within are multiple pregnancies
Identify abnormalities of the placenta, uterus, and other pelvic structures