Phew. There seem to be fewer problems associated with large babies than with small babies. Information here mainly obtained from babycentre.co.uk.
It seems the greatest risk of big baby is to mum – perineal tearing, blood loss and damage to tailbone. To baby there is less risk though there is chance of shoulder dystocia which may happen in shoulders are too large to pass through the birth canal. Related to shoulder dystocia is possible nerve damage. Baby tends to recover from both with no (or little?) long term damage. I thought I read elsewhere that there is also chance of cerebral palsy from lack of oxygen if baby has difficulty coming out.