Biparietal diameter (BPD) is measured from outer cortex of the near parietal bone to the inner cortex of the far parietal bone on a symmetric image, at the level of the thalami. Cerebellar hemispheres should not be seen in this plane. The biparietal plane is near-parallel to the ultrasound beam.
Head circumference (HC) is measured in this case by an elliptical tool on the same imaging plane.
Abdominal circumference (AC) is measured at the level of liver, preferentially at the confluence of the right and left portal veins and with stomach on view, from outer margin of skin.
Femur length (FL) measurement should be obtained with the femur perpendicular or near perpendicular to the ultrasound beam. Only the diaphysis is measured.