During the normal process of delivery, when the baby’s head is out, the leading shoulder of the baby rests just behind the pubic bone. Any delay in the prompt delivery of the baby at this point is termed shoulder dystocia. This problem occurs in about 1 to 2% of all vaginal births.
There are two major risks of shoulder dystocia: brain damage and brachial plexus injury. A shoulder dystocia taking longer than five minutes to relieve may result in damage to the baby’s brain from lack of oxygen, due to compression of the umbilical cord and lack of blood flow to the baby during the dystocia. After ten minutes, brain damage is likely. Fortunately, most shoulder dystocias can be relieved within one minute, and brain injury due to shoulder dystocia is very rare.
Brachial Plexus Injury
The brachial plexus is a cluster of nerves coming out of the neck and running down the arm. These nerves may be compressed or stretched during a shoulder dystocia, resulting in weakness or paralysis of the newborn’s arm and hand. This type of injury during shoulder dystocia is more common than brain damage but still quite rare, found in about 15% of shoulder dystocia cases.
The most common type of brachial plexus injury found at birth is called Erb’s palsy. Approximately 90% of Erb’s palsies completely resolve spontaneously or by physical therapy before the baby reaches six months. The chance of a permanent brachial plexus injury, one that will cause a lifelong disability in the arm is around one in every 10,000 births overall, and one in every 100 shoulder dystocias. It is now known that some brachial plexus injuries can occur in-utero, before the onset of labor and delivery. These types of injuries, though less common, can also result in Erb’s palsies and are unrelated to shoulder dystocia.
Other injuries sustained during shoulder dystocia include:
- fracture of the clavicle or humerus; and
- bruising of the shoulder and chest.
These problems almost always heal completely without any long-term complications.