From the Editor
Transfer to the hospital for women planning a home birth: A high-risk obstetrics problem
Do you have a written clinical guideline for pregnant women planning a home birth who are transferred to your hospital?
The ACOG report acknowledges that may cases of NBPP do occur in conjunction with shoulder dystocia and that the same biomechanical factors that predispose a fetus to develop NBPP are associated with shoulder dystocia as well. However, the report takes pains to point out that the frequent conjunction of these two entities—NBPP and shoulder dystocia—may lead to an “erroneous retrospective inference of causation.”
Risk and predictive factors
The ACOG report states: “Various risk factors have been described in association with NBPP. Overall, however, these risk factors have not been shown to be statistically reliable or clinically useful predictors for...NBPP.”
For example, fetal macrosomia, defined as a birth weight of 4,000 g or more, has been reported as a risk factor for NBPP either alone or in conjunction with maternal diabetes. Although NBPP does occur more frequently as birth weight increases, seven studies over the past 20 years have shown that most cases of NBPP occur in infants of mothers without diabetes and in infants who weigh less than 4,000 g.
Other studies have shown that, if cesarean delivery were performed in cases of suspected macrosomia, it would have only a limited effect on reducing the incidence of NBPP. Specifically, in women with diabetes who have an estimated fetal weight of more than 4,500 g, the positive predictive value for NBPP is only 5%. Without maternal diabetes, that figure is less than 2%.
Estimating fetal weight by ultrasound does not significantly enhance our ability to predict NBPP. Ultrasound estimates of birth weight usually fall within 15% to 20% of actual birth weight, and the sensitivity of ultrasound in detecting birth weights more than 4,500 g is only 40%.
Therefore, ultrasound estimates of birth weight are of limited utility for contemporaneous clinical management. Furthermore, no data exist to support the claim that estimated fetal weight can be used prophylactically to reduce the incidence of NBPP.
Recurrent shoulder dystocia may be predictive of future NBPP
Whether studied alone or with NBPP, risk factors for shoulder dystocia are not reliable predictors of its occurrence. This is not the case, however, for recurrent shoulder dystocia, where the risk of neonatal brachial plexus palsy can be as high as 4.5%, compared with 1% to 2% for a first episode of shoulder dystocia.
NBPP is a rare phenomenon
C5 and C6 roots merge to form the upper trunk, C7 root forms the middle trunk, and C8 and T1 roots merge to form the lower trunk.
Trunks and cords of the brachial plexus
The frequency of NBPP is “rare,” according to the ACOG report, which cites a rate of 1.5 cases for every 1,000 births. Favorable outcomes with complete recovery are estimated to range from 50% to 80%.3
Brachial plexus injuries are classically defined as Erb’s palsy—involving C5 and C6 nerve roots—or Klumpke’s palsy, in which there is damage to the C8 and T1 nerve roots.
Erb’s palsy is recognizable by the characteristic “waiter’s tip” position of the hand, which is caused by muscle imbalance in the shoulder and upper arm. Most NBPP injuries are Erb’s palsy, which affect 1.2 infants in every 1,000 births.
Klumpke’s palsy results in weakness of the hand and medial forearm muscles. It affects 0.05 infants in every 1,000 births. The remaining cases involve a combination of the two types of palsy.
These injuries can be temporary, resolving by 12 months after birth, or permanent. The rate of persistence of NBPP at 12 months ranges from 3% to 33%.
Can clinician maneuvers increase the likelihood of NBPP?
The ACOG report addresses the direction and angle of clinician traction at delivery. The report confirms what clinicians generally have been taught: The application of fundal pressure during a delivery in which shoulder dystocia is recognized can exacerbate shoulder impaction and can lead to an increased risk of NBPP.
Traction applied by the clinician and lateral bending of the fetal neck often are implicated as causative factors of NBPP. However, ACOG presents evidence that NBPP can occur entirely unrelated to clinician traction. The report cites studies involving both transient and persistent NBPP in fetuses delivered vaginally without evident shoulder dystocia. The same types of injury are sometimes seen in fetuses delivered by cesarean, as has been mentioned.
The report goes on to state:
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.
