dystocia and brachial plexus injury be prevented?
Up until this point we have been
looking for various ways of predicting which babies and which
labors will experience shoulder dystocia and possible brachial
plexus injury. But such predictions, even if they can be made,
are useless if there is no way to alter labor and delivery
management so as to prevent shoulder dystocia and
brachial plexus injury from occurring. Thus a most important
question is this: Given what we know about shoulder dystocia
and brachial plexus injury, is there anyway to prevent them?
As with the question of the predictability of shoulder dystocia, the answer to the question as to whether or not shoulder dystocia can be prevented has changed with the work of Gudmundsoon (2005) and Mazouni (2006) linking maternal size and fetal weight with shoulder dystocia and with the development of Hamiltonís shoulder dystocia risk predictive tool. Certainly if 50% or more of shoulder dystocias can be accurately predicted with a low false positive rate (2.7%), then prophylactic cesarean section for those patients thus identified becomes a reasonable preventive strategy. As further experience with the shoulder dystocia screening tool accumulates, this may well become the standard of care for attempting to prevent shoulder dystocia.
Up until this 2006, however, this tool had not been available. Let us look, therefore, at what information obstetricians have had up till now concerning the preventability of shoulder dystocia.
From the options available to
obstetricians for intervening in pregnancy, labor and delivery, the only
possible means for preventing shoulder dystocia would be:
- To perform elective
cesarean sections for suspected macrosomia
- To induce labor in
pregnant patients before their due dates in hopes of
preventing babies from becoming macrosomic
- To attempt through diet or
blood sugar control to limit maternal weight gain
There are some authors who have always felt that shoulder dystocia could be prevented. O'Leary, in his
book on shoulder dystocia, states:
obstetrician or midwife can anticipate this problem
[shoulder dystocia] as a result of routinely identifying
those risk factors that predispose to shoulder dystocia.
Thus prevention requires identification of risk factors,
which leads to anticipation of the problem . . .
Identification of critical risk factors will lead to
anticipation, which in turn will lead to prevention.
O'Leary then boldly goes on
The presence of macrosomia
of 4500 g alone is justification for cesarean section in
nonobese women. The presence of macrosomia of 4000-4500 g
may in itself be sufficient to warrant abdominal delivery
when other risk factors, especially a platypoid (flat)
pelvis, diabetes and/or obesity, are present.
But despite the certitude of
his statements, O'Leary presents no data to support his
Other authors have also tried
to articulate guidelines for avoiding shoulder dystocia.
Anchor (1988) has said:
We advocate the abdominal
mode delivery for infants of diabetic gravidas whose best
estimated fetal weight exceeds 4000 g.
Langer (1991) stated that if
all infants of diabetic mothers who weighed 4250 g or more
were delivered by cesarean section, the overall cesarean
section rate would increase by only 0.26% while shoulder
dystocia would be reduced by 76%. He goes on to acknowledge,
however, that in the nondiabetic group there is no weight that
provides an optimal threshold for cesarean section to avoid
But statements such as these have represented the far fringe of obstetrical opinion. It has been the consensus of the vast majority of obstetricians who have studied the subject that there was no real way to figure out which babies are likely enough to have shoulder dystocia to warrant changes in the management of their labors. The basic issue is this: One can suspect shoulder dystocia all one wants. But is there some combination of factors that predicts shoulder dystocia with an accuracy great enough to make doing cesarean sections, performing early inductions, or making other changes in management a reasonable course of action? The answer up until now has been "No." Below is listed evidence that has supported this conclusion:
Basket (1995) : The profile
of risk for shoulder dystocia -- prolonged pregnancy,
prolonged second stage of labor, macrosomia, and assisted
mid-pelvic delivery -- were not clinically useful because
"the large majority of cases of shoulder dystocia occur in
patients without these risk factors"
Resnick (1980): Most babies
with shoulder dystocia do not have risk factors. "The
diagnosis will often be made only after delivery of the
Gherman (2002): "Most of
these preconception and prenatal risk factors have extremely
poor positive predictive values and therefore do not allow
the obstetrician to accurately and reliably predict the
occurrence of shoulder dystocia."
Lewis (1998): Only 25% of
shoulder dystocia cases had at least 1 significant risk
Acker's (1986) : Almost
half (47.6%) of all shoulder dysoticas occurred in babies
weighing less than 4000 g.
Cunningham, author of
Williams Obstetrics, reports that 99.5% of babies
weighing 4000-4500 gms had a safe vaginal delivery without
Al-Najashi (1989) stated
that 41% of shoulder dystocia deliveries occurred in infants
of average birth weight, that is 2500 to 3999 g.
Eckert (1997): The greatest
number of injuries occurred in nondiabetic patients with
birth weights of less than 4000 g.
It is certainly clear that
there are risk factors which do increase the odds of shoulder
dystocia and brachial plexus injury occurring. But so many
babies with each of these risk factors do not encounter
shoulder dystocia and brachial plexus injury that it is
difficult to justify changes in management of all labors on
the basis of these suspicions.
Despite his statements in his
1992 book, even O'Leary, in a 1990 paper, acknowledges the
unpredictability of shoulder dystocia: He lists multiple risk
factors for shoulder dystocia -- and then goes on to prove
that the majority of macrosomic babies do not have these
The entire issue is best
summed up in Practice Bulletin #40 "Shoulder Dystocia" (2002)
by the American College of Obstetricians and Gynecologists.
They find the preponderance of current evidence consistent
with the following positions:
3. Most cases of shoulder
dystocia cannot be predicted or prevented because there are
no accurate methods to identify which fetuses will develop
4. Ultrasonic measurement
to estimate macrosomia has limited accuracy
5. Planned cesarean section
based on suspected macrosomia is not a reasonable strategy
6. Planned cesarean section
may be reasonable for the nondiabetic with an estimated
fetal weight exceeding 5000 g or the diabetic whose fetus is
estimated over 4500 g
Up until this year, the vast bulk of the medical literature continued to support these contentions. However given the new work of Hamilton and her co-workers, these statements may have to be re-evaluated over the next several years.
Would elective cesarean section for
suspected macrosomia be a reasonable strategy for decreasing
the number of shoulder dystocias and brachial plexus injuries?
Many papers have been written
trying to assess the utility of performing cesarean sections
for suspected macrosomia in an attempt to reduce the risk of
shoulder dystocia and permanent brachial plexus injury.
Gonen (2000) studied the use
of physical examination and ultrasound during labor to
identify babies suspected of being greater than 4500 g. His
goal was to see if by performing cesarean sections in these
cases he could reduce the rate of permanent brachial plexus
injury. Macrosomia was suspected in 47 cases -- but was only
confirmed at cesarean delivery in 21 of these (45% positive
predictive value). Thus there were 26 unnecessary cesarean
sections due to a false diagnosis of macrosomia. Moreover,
over 84% of the macrosomic babies born from his subject
population were missed. Of the 115 cases of macrosomia, only
21 were correctly identified in labor -- a dismal sensitivity
rate of 18.3%. Of the 17 babies that developed brachial plexus
injuries in his study, three were macrosomic -- but they were
not identified prior to or during labor! The remaining 14
injured babies were not macrosomic. Thus, Gonen's attempt to
decrease the brachial plexus injury rate by performing
cesarean sections on suspected macrosomic babies missed most
big babies and resulted in many unnecessary cesareans. He
confirmed what is a major problem with any attempt to predict
and prevent shoulder dystocia and brachial plexus injury:
The group in which they occur most often is that of normal
Many other studies have
resulted in similar conclusions:
Rouse and Owen (1999) showed
that prophylactic cesarean section would require more than
1000 cesarean sections and millions of dollars to avert a
single permanent brachial plexus injury.
Basket (1995) stated that if
in his series of patients all mid-forceps deliveries had been
replaced by cesarean sections, 3268 cesarean section
deliveries would have been performed to prevent 16
non-permanent brachial plexus injuries. Even if cesarean
sections were performed only for babies suspected of being
greater than 4500 g, 54 cesarean sections would have to be
performed to prevent one case of non-permanent brachial plexus
Eckert, in his 1997 paper,
sums up the problem neatly:
In practice, only estimates of fetal weight, not actual
weights, are available to practitioners seeking to predict
the risk of birth injury. Weights estimated before delivery,
whether by ultrasound or clinical estimation, are
notoriously inaccurate. Even if we were able to identify a
specific fetal weight that mandated cesarean section, any
scheme that relied on estimated fetal weight to risk
patients into cesarean delivery would result in the delivery
of many infants appreciably smaller than the estimated fetal
weight assigned them.
He points out that
The greatest number of
injuries occurred in nondiabetic pregnancies with birth
weights less than 4000 g. No protocol for managing
macrosomia recommends cesarean delivery for estimated fetal
weight of less than 4000 g.
In our opinion, the number
of cesarean sections necessary to prevent a single birth
injury in a normal glycemic population precludes our
recommending mandatory cesarean delivery at any weight
Delpapa (1991) studied
nondiabetic women thought on ultrasound to have macrosomic
fetuses. He concluded that he would have to do 76 cesarean
sections to prevent five cases of shoulder dystocia:
Our study does not support
the contention that elective cesarean section is justified
in those women with fetuses suspected to be macrosomic as a
means of preventing persistent infant mortality. A very
large number of unnecessary cesarean sections would be
performed without much preventive effect.
McFarland (1986) presented
data by weight group showing how many cesarean sections would
need to be performed to prevent even temporary brachial plexus
His conclusion is that even
if a reliable means of estimating fetal weight were possible,
by performing cesarean sections for all babies estimated to be
greater than 4500 g only 32% of all shoulder dystocias would
be avoided. At any lower weight cut off, there would be far
too many cesarean sections for far too little gain.
Rouse also tried to quantify
the effectiveness of a policy of elective cesarean section for
ultrasound-diagnosed fetal macrosomia. He found that in women
without diabetes, if a cesarean section were performed for
each baby with a suspected weight of greater than 4500 g, 3695
cesarean sections would have to be performed at an additional
cost of $8.7 million for each permanent brachial plexus injury
Bryant (1998) data showed
that even assuming ultrasound diagnosis to be accurate in
predicting fetal weight, between 155 and 588 cesarean sections
would have to be performed to obviate a single case of
permanent injury, depending on the weight cut-off selected:
Our data show that a policy
of elective cesarean delivery in cases of suspected fetal
macrosomia had an insignificant effect on the incidence of
brachial plexus injury. Although the contribution of this
policy to the cesarean delivery rate was small, the number
of cesarean deliveries required to prevent a single case of
permanent brachial injury was high and probably
Gregory (1998) stated that if 5.5% of all brachial plexus
injuries were permanent -- which his data demonstrated -- only
one in 3833 macrosomic infants would have a persistent Erb
palsy. Moreover, he found that one half of all of the
shoulder dystocias in his series occurred in normal weight
Kolderup (1997) found that a policy of elective cesarean
section for macrosomia would necessitate 148 to 258 cesarean
sections to prevent a single persistent injury. He feels
that "these findings support a trial of labor and judicious
operative vaginal delivery for macrosomia infants."
Sandmire (1993) discusses the difficulty in attempting to
determine fetal size in utero:
Any approach using ultrasound would have to demonstrate that
its use improves newborn or maternal outcome without
disproportionate increases in morbidity and mortality. A barrier to achieving
this goal is the inaccuracy associated with estimation of fetal
weight. The current ultrasonic procedures for estimation of fetal weight are not
accurate enough for detecting macrosomia defined by weight criteria.
And even if clinicians could determine fetal weight
accurately, the frequency of persistent fetal injuries associated with
vaginal birth of the macrosomic fetus is so low that induction of labor or
birth is not justified on that basis. Delivery decisions
based on inaccurate
estimated fetal weights should be avoided.
He also composed a chart drawn from data in several other
studies in which he evaluated the rate of permanent brachial
plexus injuries and the number of cesarean sections that
would be necessary to avoid them:
C/S to prevent BPI injuries
C/S to prevent permanent
Sandmire (1996) concludes that a policy of employing
cesarean section for suspected macrosomia in hopes of
preventing permanent brachial plexus injury will not work
1. The inaccuracy of ultrasound in estimating fetal weight
2. The increases in morbidity and mortality that would occur
from the very large numbers of cesarean sections so
3. The many cesarean sections would have to be done to
prevent one significant fetal injury
Sandmire also takes care to distinguish minor injuries, such
as clavicular fracture and transient brachial plexus injury,
from severe persistent fetal injuries. He admonishes anyone
considering the issue of cost vs. benefit in the management
of suspected macrosomia to make decisions based only on
significant fetal injuries, such as permanent brachial
plexus injuries and severe neurologic damage.
Summarizing, the major conclusion of most of the obstetrical
literature discussing the strategy of performing cesarean
sections for suspected macrosomia is that it would not be
practical because it would require far too many unnecessary
interventions for the benefits that would be obtained.
Cesarean sections are not without risk, especially for
diabetic and/or obese women
Although cesarean section is one of the most commonly
performed operations in the United States, it still carries
much greater risk than does a vaginal delivery. These risks
include blood loss, infection, damage to other pelvic
organs, and respiratory emergencies. Moreover, the recovery
period is longer and more painful and performing one
cesarean section greatly increases the likelihood that a
woman will have her next baby by cesarean section as well.
Finally, total hospital care for women delivering a baby via
cesarean section is 50%-100% more expensive than the cost of
a vaginal delivery.
Thus in order to justify the increased risk, pain, and
expense of performing cesarean section in hopes of avoiding
shoulder dystocia and permanent brachial plexus injury,
there has to be substantial evidence that this is an
effective policy. As has been shown, such evidence has up until now been lacking. In fact, the evidence has been contrary to this supposition.
What about early inductions as a means of avoiding shoulder
dystocia and brachial plexus injury?
Many have thought that by cutting off one to two weeks of
growth of a fetus at term, a baby might be delivered small
enough to avoid shoulder dystocia and the risk of permanent
brachial plexus injury. The problem with this theory is that
there is no data to support it.
In the first place, the growth rate of babies differs
significantly, both between babies and at various points in
pregnancy for each baby. Thus it is impossible to estimate
how much additional growth is prevented by "early delivery".
Most importantly, studies looking at this means of
attempting to prevent shoulder dystocia have never been
successful in reducing the number of macrosomic babies or
showing that such a program reduces the risk of shoulder
Del Papa (1991) found that early induction did not decrease
Gonen (1997) randomized patients suspected of macrosomia
based on ultrasound examination to an early induction
group -- 134 patients -- or a routine pregnancy follow-up
group -- 139 patients. There was no statistically significant
difference in shoulder dystocia between the two groups.
Several authors -- Leaphart (1997), Friesen (1995), Combs
(1993) -- have even shown that this approach of early induction
actually increased the cesarean section rate with no
decrease in the incidence of shoulder dystocia.
So, can shoulder dystocia be prevented?
A review of the literature indicates that the answer to this question has up until this year been "No." Estimates of fetal weight are unreliable. It is impossible to accurately tell which babies will be macrosomic. And it has previously been impossible to reliably determine which babies will develop shoulder dystocia. Based on previous information available to obstetricians, a policy of prophylactic cesarean section would have required huge numbers of operations to prevent a single case of permanent brachial plexus injury. It is also the case that a policy of elective induction has not been shown to decrease the number of shoulder dystocias.
Hope for the future
As has been discussed, there is now published research, based on sophisticated statistical and mathematical analysis of a large numbers of shoulder dystocia cases, that shows that it is possible to identify 50% or more of those mothers and fetuses at highest risk for shoulder dystocia.
Dr. Emily Hamilton and her team of researchers in Montreal have developed a formula considering maternal height, maternal weight, parity, gestational age, estimation of babyís weight, and maternal history of gestational diabetes or previous shoulder dystocia that, when tested against several large independent samples of patients who had experienced shoulder dystocia with permanent injury, consistently identified 50-70% of them with a false positive rate (rate of additional cesarean sections) of only 2.7%. (Dyachenko,Hamilton 2006 and subsequent unpublished data). This tool has been commercialized into a web-based application by LMS Medical Systems and labeled the CALM Shoulder ScreenTM (patent pending) -- see
http://www.lmsmedical.com) for more information.
As this probabilistic tool becomes more widely utilized, it may well be possible to prevent a significant proportion of brachial plexus injuries by recommending prophylactic cesarean section to those women identified as being at high risk for shoulder dystocia.
Copyright © 2006 Henry Lerner