According to Benacerraf et al (note the use of millimeters):
expected humerus length in mm =
= (0.8492 * (biparietal diameter in mm)) - 7.9494
In Figure 3 of Rodis et al, the middle line of humerus vs biparietal diameter in cm can be modeled by the equation:
expected humerus length in cm =
= (0.7309 * (biparietal diameter in cm)) - 0.3745
ratio of observed to predicted humerus length =
= (length observed) / length predicted)
Limitations:
• Good ultrasonographic images with accurate measurement using electronic calipers are required.
NOTE: On page 1053 Rodis et al give the following equation
expected humerus length in cm =
= (1.146 * (biparietal diameter in cm)) + 1.14
but this gives results that do not match any of the data in the paper.
