Various risk factors have been described in association with NBPP. They include fetal malposition, labor induction, labor abnormalities, operative vaginal delivery, fetal macrosomia, and shoulder dystocia. Overall, except for shoulder dystocia, these risk factors have not been shown to be statistically significant or clinically useful predictors for the occurrence of NBPP. Most NBPP cases (greater than 80%) occur in women without known risk factors. Risk factors for shoulder dystocia are not reliable predictors for its occurrence or the occurrence of NBPP. Thus, no intervention has been identified that will prevent all or even most cases of NBPP or clinically apparent shoulder dystocia.
Notwithstanding the unreliability of specific risk factors to predict NBPP or clinically apparent shoulder dystocia in a specific case, there are three clinical situations of concern to practitioners in which an alteration of usual obstetric management might be considered to reduce the risk of shoulder dystocia and brachial plexus injury: 1) suspected fetal macrosomia with estimated fetal weight exceeding 5,000 g in women without diabetes or 4,500 g in women with diabetes; 2) prior recognized shoulder dystocia, especially with a severe neonatal injury; and 3) midpelvic operative vaginal delivery with fetal birth weight more than 4,000 g. Even in these circumstances, the occurrence of NBPP is relatively low, and with proper informed consent, numerous clinical situations exist in which these risk factors alone should not dictate a particular course of management. Chapter 2 discusses risk factors in more depth.
Chapter 3 delves into the pathophysiology and biomechanics of NBPP. Uterine contractions and maternal pushing efforts produce pressure within the uterus that is transmitted by direct contact and through amniotic fluid. This pressure produces a force that moves the fetus into and through the pelvis. Both maternal (endogenous) forces and clinician-applied (exogenous) forces have a direct effect on the fetus as a whole and on its discrete anatomic structures. Maternal forces alone are an accepted cause of at least transient NBPP by most investigators. In addition, NBPP can be caused by downward lateral traction applied by the birth attendant. Downward lateral traction (bending of the fetus’ neck away from the anterior shoulder, toward the posterior shoulder or floor) has been shown to place greater strain on the brachial plexus than downward axial traction, wherein the applied forces are parallel to the fetus’ cervicothoracic spine. Nonetheless, even properly applied axial traction can result in NBPP, as discussed further in Chapter 3.
Neither high-quality nor consistent data exist to suggest that NBPP can be caused only by a specific amount of applied force beyond that typically used by health care providers during any delivery. Instead, available data suggest that the occurrence of NBPP is a complex event, dependent not only on the forces applied at the moment of delivery, but also on the constellation of forces (eg, vector and rate of application) that have been acting on the fetus during the labor and delivery process, as well as individual fetal tissue characteristics (eg, in situ strain and acid–base balance). In addition to research within the obstetric community, the pediatric, orthopedic, and neurologic literature now stress that the existence of NBPP following birth does not a priori indicate that exogenous forces are the cause of this injury.
Shoulder Dystocia and Neonatal Brachial Plexus Palsy
Chapter 4 addresses the association of shoulder dystocia and NBPP. A commonly accepted definition of shoulder dystocia is a delivery that requires additional obstetric maneuvers following failure of gentle downward traction on the fetal head to effect delivery of the shoulders. Clinically, shoulder dystocia is diagnosed after delivery of the fetal head when the anterior shoulder fails to emerge under the pubic rami as a result of impaction of the fetus’ anterior shoulder behind the pubic symphysis. Although in most cases, a combination of factors raises suspicion that shoulder impaction against the pubic symphysis has occurred, shoulder dystocia is not formally diagnosed until a trial of downward axial traction has been unsuccessful in delivering the anterior shoulder. Recognized shoulder dystocia occurs infrequently, with an incidence ranging from 0.2% to 3.0% of all vaginal deliveries. It appears that the incidence of clinically evident shoulder dystocia has been increasing over the past several decades. Nonetheless, the incidence of NBPP has remained relatively constant over time. Current and emerging approaches to the management of shoulder dystocia also are discussed in Chapter 4 and further detailed in the appendixes.
Anatomy, Presentation, and Assessment
The brachial plexus is a very complex structure that connects the spinal nerves to their terminal branches in the upper extremity. Understanding the schematic anatomy of the nerves and the muscles they innervate provides a critical foundation from which to understand the clinical presentation of NBPP. Anatomic variation of the plexus can occur among the spinal roots that contribute to the brachial plexus and can subsequently affect the clinical presentation. Chapter 5 describes factors affecting the clinical presentation of NBPP and gives a detailed summary of anatomic considerations.
Determining when an injury to the neonatal brachial plexus occurred may have prognostic as well as medicolegal implications; therefore, the timing should be assessed whenever possible and relevant events and findings thoroughly documented. Birth attendants may suspect NBPP on the basis of initial observations of the neonate. However, the ultimate diagnosis is best achieved by the combined efforts of neonatologists, neurologists, pediatricians, physiatrists, and occupational and physical therapists. If NBPP is suspected, the treating clinician should assess the infant for skeletal injuries and fractures by clinical and radiographic examination because some musculoskeletal injuries preclude early therapy for NBPP. Components of the physical examination and assessments are described in Chapter 5. Assessment scales in NBPP are used to gauge the extent of injury, prognosticate potential recovery, and determine further treatment, as well as evaluate overall function.
Patterns and Early Intervention
Chapter 6 describes patterns of NBPP. In NBPP, the upper plexus is affected more frequently (Erb palsy) than either the lower plexus alone (classic Klumpke palsy) or the complete nerve complex. The natural history of NBPP, around which the determination of optimal treatment revolves, remains the subject of debate in many published reports. The complete potential scope of NBPP is difficult to define because of the various combinations of lesions within the elements of the brachial plexus. Further difficulties include the definition of recovery and the potential bias introduced by the referral patterns of reporting physicians because many patients with Erb palsy recover spontaneously and are not referred to the specialists who publish most reports. Whereas early clinical improvement is ultimately associated with favorable outcomes, most practitioners agree that as an absence of spontaneous clinical improvement persists, the potential for recovery diminishes.
Chapter 6 goes on to address indications for surgery for NBPP. The indications for surgical nerve reconstruction in NBPP vary widely among different practitioners. However, most agree that early nerve reconstruction should be recommended for panplexopathy and preganglionic nerve root lesions. Overall, infants who sustain NBPP have a good prognosis, with the majority recovering adequate functional use of the affected arm without surgical intervention. Early occupational and physical therapy can support spontaneous recovery of function and minimize musculoskeletal comorbidities. Given recent and continuing improvements in surgical and conservative treatments, early referral to a specialty care center can improve overall outcomes after NBPP.
The report reviews the peer-reviewed and other pertinent literature on NBPP with special emphasis on its pathophysiology and causation. Some strategies that demonstrate either a reduction in NBPP or an increased rate of successful resolution of shoulder dystocia are included, but the work does not present comprehensive management strategies. Moreover, no single management strategy is viewed as preferable.
The primary objective in the presence of clinically recognizable shoulder dystocia continues to be the delivery of the fetus before the fetal brain experiences hypoxic–ischemic injury. Any intervention to effect delivery must necessarily balance the risk of using ancillary maneuvers, which will increase strain on the fetus’ brachial plexus, against the risk of hypoxic–ischemic brain injury. The birth attendant is the individual best equipped to assess this balance and decide on the type and degree of intervention.
Significant advances have been made in the science of biomedical engineering that have informed this document and that will continue to increase the understanding of the mechanical forces that affect the fetus during labor and delivery. In the years to come, the greater sophistication of physical and computer models will enhance the ability to assess the effects of both endogenous forces of labor and delivery and exogenous forces generated by the birth attendant in facilitating an obstructed delivery.
The task force recognizes that knowledge about NBPP is continually evolving. What is known at this time with reasonable medical certainty is that NBPP occurs infrequently and can be caused by maternal (endogenous) forces or clinician-applied (exogenous) forces or a combination of both. Similarly, NBPP can occur with or without associated, clinically recognizable shoulder dystocia. Finally, in the presence of shoulder dystocia, all intervention by way of ancillary maneuvers—no matter how expertly performed—will necessarily increase strain on the brachial plexus.