If my first son had a brachial plexus injury at birth, what are the chances that my next child will as well?

Variable: In general, brachial plexus injury is not felt to be hereditary. However, depending on the cause of the injury, there may be increased risk with subsequent pregnancies. For example, if the woman has an unusually small pelvis, or tendency to have unusually large babies (e.g., due to diabetes) the chance for difficulty during vaginal delivery, and subsequent brachial plexus injury, is increased.

Significant.: Large infants, maternal obesity and diabetes mellitus all conspire to a high recurrence risk for shoulder dystocia; this has been found to be as much as 1 to 25% in retrospective studies (probably an underestimation of the true recurrence risk as most mothers and clinicians choose an abdominal delivery in pregnancies subsequent to an episode of shoulder dystocia). Pre-labor c-section recommended!

See below: Brachial plexus injuries usually occur during a difficult pregnancy. Essentially the shoulder gets trapped and stretches these nerves during delivery. Talk to you obstetrician about what can be done to avoid this problems. This might include c-section, epidurals or other techniques.