Obstetric Brachial Plexus Injury

Factors Increasing Risk of Shoulder Dystocia

What factors must doctors and expecting parents consider when assessing the risk of an obstetric brachial plexus injury?

Brachial Plexus Birth Injuries (OBPI)
Brachial plexus birth injuries are a regular part of pediatric practice both in the delivery room and newborn surgery. Unlike other birth injuries of the nervous system, their prognosis is better.

The incidence of birth injury of the plexus has been reported as between 0.13 and 3.6 cases per 1,000 live births. Recent, prospective studies report incidences clustering around 1 per 1,000 live births or somewhat lower if only severe injuries are counted. Many have expressed the hope that improved obstetric techniques, including the more frequent use of caesarian section, might lower this figure but recent data have not substantiated this. Elective cesarean section provides some protection but does not completely eliminate the risk of brachial plexus injury.

Brachial Plexus Problems: Old and New
In practical terms shoulder dystocia is not a difficult diagnosis to make. After the baby’s head is delivered over the mother’s perineum, it appears to snap back against her vulva. The head becomes congested and cyanotic. It becomes clear that the shoulders are stuck in the pelvic area.

The first thing an obstetrician does is apply downward pressure to the head – sometimes forcefully. The gentle downward tug is a standard maneuver, however, just because it is done frequently doesn’t mean that it’s the correct thing to do.

Experts recommend that when shoulder dystocia is evident, one must not touch the head even gently until after the shoulder impaction is corrected. Pulling on the head – even gently – increases the risk of brachial plexus injury.

Fifty percent of the babies who have shoulder dystocia problems weigh less than 8 pounds 14 oz. The vast majority of these babies recover with no permanent brachial injuries. Five to 25 percent of shoulder dystocia may result in brachial plexus injuries. The key to avoiding brachial injury is gentle traction not excessive or medium force.

Healthcare providers whether they are midwives or specialists must have expertise to manage shoulder dystocia because the condition is not known until it appears. Inappropriate excessive tractions can deliver 50 to 75 pounds of pressure to the fetal head as compared to 2 to 3 pounds of pressure from gentle traction.

Erb’s Palsy is not an impact injury in labor; it is a stretch injury. The shoulder doesn’t reach the pubic bone until the head is out. Damage to the brachial plexus will only occur after the nerves have been stretched 25 percent. Such stretching doesn’t occur in labor.

Risk Factors and Causes
Maternal diabetes, large birth weight for other reasons, prolongation of the second stage of labor, the use of forceps, shoulder dystocia, and older maternal age are all risk factors.

Early doctrines held that plexus injury was caused by clavicular compression, by fracture of the proximal humerus, or by the neurotoxic effects of effusions escaping from the torn capsule of an injured glenohumeral joint.

The anterior shoulder becomes impacted against the pubic bone and a downward force applied to the head to dislodge the shoulder puts the brachial plexus on the stretch. Shoulder dystocia is noted in the obstetric record in about 50 percent of brachial plexus injuries incurred in the course of vertex vaginal deliveries. One possibility is that shoulder dystocia actually occurs in these cases but that the attendants fail to record it.

Without known reason, the authors concluded that shoulder dystocia had been under- recorded, but logic and subsequent commentators agree that the correct conclusion is that the injury-without-dystocia births were different phenomena from the dystocia-with-injury births; likewise, obstetric factors such as birth weight, maternal age, and parity distinguished injuries associated with shoulder dystocia from injuries not associated with shoulder dystocia. Injuries without dystocia were more severe, took longer to resolve, were more frequently associated with a clavicular fracture, and more frequently affected the posterior arm. They concluded that injuries with and without associated dystocia were qualitatively different. Thus the obstetrician’s efforts to relieve shoulder dystocia are not the whole explanation for brachial plexus birth injuries. The last word on the brachial plexus injury matter has not been spoken.

Sources:
Joseph H. Piatt, St. Christopher’s Hospital for Children, Philadelphia, PA & Textbook of Pediatrics, Chapter 7, the Newborn Infant