The length of the humerus can be predicted from the biparietal diameter in a normally developing fetus.


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)



• 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.


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