If you have high blood sugar levels, your baby may grow to be larger than usual. This is because she/he has to make extra insulin to control the increased blood sugar, which causes more fat and tissue to be stored. This can make delivery difficult. E. g, there is an increased risk of shoulder dystocia-your baby's head has been born but one of his or her shoulders is stuck behind your pelvic bone, preventing the body being delivered. This in turn can damage nerves in your baby's neck or result in a fracture of one of his or her arms or shoulders. Very rarely, it can cause brain damage if the blood supply to your baby's brain is blocked off for too long.
Attribution: BUPA