Mesomelia refers to abnormal shortening of the mid segment bones of the limbs
(radius and ulna in upper and tibia
in lower limb). This is often associated with several syndromes, some of which can even be fatal. There is no mention of upper limb mesomelia in the upper limbs. Iolated mesomelia has a better prognosis especially when not syndromic and the babies may do well health-wise but will remain dwarfed.
It would be advisable to meet your obstretician for further advise and management. Also, since it is a grave condition, it may help to get another anomaly USG scan done by a different radiologist
for confirmation before taking any major decision.