This is a good measurement of the abdominal circumference. It satisfies a number of criteria:
- the abdomen is not foreshortened (true axial measurement)
- the full circumference of the abdominal wall is visible
- the calipers are placed at the level of the skin (not deep to the ribs)
- the gastric bubble can be seen
The other landmarks, the umbilical vein and portal sinus, could not be seen in this fetus, presumably due to early age. At the standard 18-20 week exam, these structures would have to be identified.