Brachial plexus palsy: intrauterine onset.

A newborn had a combination of brachial plexus palsy and phrenic nerve palsy associated with a small left arm, deformed ribs on the left, and an area of subcutaneous calcification on the left side of the neck. These lesions represent a deformation syndrome due to uterine constraint in a bicornuate uterus. Appropriate diagnosis can initiate management to avoid problems in subsequent pregnancies.