distocia de homrbo

1. Shoulder Dystocia:
Incidence and Risk
Factors
JOSEPH G. OUZOUNIAN, MD
University of Southern California, Keck School of Medicine,
Los Angeles, California
Abstract: Shoulder dystocia complicates B1% of
vaginal births. Although fetal macrosomia and ma-
ternal diabetes are risk factors for shoulder dystocia,
for the most part its occurrence remains largely
unpredictable and unpreventable.
Key words: macrosomia, shoulder dystocia, gesta-
tional diabetes
The most common definition for should-
er dystocia is a delivery that requires
additional obstetric maneuvers after gen-
tle downward traction on the fetal head is
unsuccessful in delivery of the shoulders.1
Careful review of 29 peer-reviewed stud-
ies published from 1985 to 2016 demon-
strates an incidence of shoulder dystocia
ranging from 0.1% to 3.0% of all deliv-
eries, with a clinically useful average
incidence of about 1%.1–29
This wide
range may be attributable to variations
in the study populations analyzed, incon-
sistencies in shoulder dystocia diagnosis,
and methodologic variation (eg, reliance
on medical record coding vs. direct med-
ical record review, etc.).
Although the majority of shoulder
dystocia cases occur in infants with birth-
weight less than 4000 g, fetal macrosomia
increases the risk for shoulder dysto-
cia.1,18
In 2013, Ouzounian et al18
studied
221 cases of shoulder dystocia from a
cohort of 13,277 vaginal deliveries, and
demonstrated that more than half
(50.7%) occurred in infants that weighed
<4000 g. However, the mean birthweight
in the shoulder dystocia group was
4011 ± 452 versus 3390 ± 447 g in the
no shoulder dystocia group (P<0.001).
Furthermore, <1% of the nonshoulder
dystocia patients had a birthweight
>4500 g, compared with 14.5% in the
shoulder dystocia group (P<0.001). Oth-
er investigators have demonstrated sim-
ilar trends. For example, at least 2 studies
showed that the incidence of shoulder
dystocia increases with every 500 g of
birthweight, with a 10-fold increased
incidence when birthweight was over
4500 g.30,31
In fact, in Stotland’s
study, the incidence of shoulder dystocia
was 23% when birthweight was over
5000 g.31
Although the association of high birth-
weight and shoulder dystocia is indeedThe author declares that they have nothing to disclose.
Correspondence: Joseph G. Ouzounian, MD, Univer-
sity of Southern California, Keck School of Medicine,
Los Angeles, CA. E-mail: joseph.ouzounian@med.
usc.edu
CLINICAL OBSTETRICS AND GYNECOLOGY / VOLUME 59 / NUMBER 4 / DECEMBER 2016
www.clinicalobgyn.com | 791
CLINICAL OBSTETRICS AND GYNECOLOGY
Volume 59, Number 4, 791–794
Copyright r 2016 Wolters Kluwer Health, Inc. All rights reserved.
Copyright r 2016 Wolters Kluwer Health, Inc. All rights reserved.

2. compelling, it remains a clinical conun-
drum for contemporaneous patient man-
agement, in light of our continued
inability to predict birthweight accurately
using either ultrasound or clinical meth-
ods. Typically, ultrasound estimates of
fetal weight are within 20% of the actual
birthweight in 95% of cases. In the
remaining 5%, the estimate will have an
error rate >20%.32,33
Clinical estimates
using abdominal palpation, fundal height,
or maternal estimation do not perform
any better. In a recent study evaluating
the effects of suspected macrosomia on
outcome, King and colleagues demon-
strated that the sensitivity of ultrasound
and abdominal palpation for identifying
macrosomia before delivery was 40.2%
and 15.1%, respectively. Furthermore,
most studies evaluating the relationship
between fetal macrosomia and birth-
weight use actual birthweight to describe
the association.
To help clarify this matter further, in
2016 Ouzounian et al2
studied clinical
risk factors for shoulder dystocia and
compared risk factor prediction models
using estimated fetal weight versus actual
birthweight. The risk factor models were
analyzed rigorously using multivariable
logistic regression techniques, and neither
model demonstrated clinically useful sen-
sitivity or positive predictive value for
unequivocal prediction of shoulder dys-
tocia before delivery.2
Even with these
limitations in mind, it is generally helpful
to have a good faith estimate of fetal
weight before delivery to assist with
patient counseling, delivery planning,
and intrapartum management. The
American College of Obstetricians and
Gynecologists has set forth clinical
thresholds of 4500 and 5000 g (for dia-
betics and nondiabetics, respectively).34
Thus, in a hypothetical example where a
patient has a clinical fetal weight estimate
of 4400 g, after appropriate counseling
vaginal delivery might still be attempted,
but the estimate may trigger an informed
consent discussion before delivery, and
may also preclude an attempt at opera-
tive vaginal delivery with forceps or
vacuum intrapartum.
Maternal diabetes is another risk fac-
tor for shoulder dystocia.35
Maternal
diabetes, whether gestational or pregesta-
tional, can result in fetal macrosomia,
which is a risk factor for shoulder dysto-
cia in and of itself as discussed above. In
addition, when compared side by side,
infants of diabetic mothers have an in-
creased risk for shoulder dystocia even
with normal birthweight, due to the
potential dysmorphic features often seen
in these infants. Physiologically, infants
of diabetic mothers have thicker upper
extremity skinfolds, higher body fat, and
broader shoulders. They also have an
increased incidence of asymmetric growth
patterns. These findings, taken together,
can result in an increased risk for should-
er dystocia.36–41
Although the diagnosis
of maternal diabetes does not preclude
vaginal delivery in and of itself, it may
warrant careful fetal weight estimation,
informed consent, and individualized
delivery planning.
A history of prior shoulder dystocia is
an important risk factor for recurrence.
Studies of recurrent shoulder dystocia
consistently have demonstrated increased
rates of shoulder dystocia in subsequent
pregnancies. The rate may be even higher
than reported, given that many patients
who had shoulder dystocia in a prior
pregnancy may not have additional chil-
dren, or may deliver through cesarean
section in a subsequent pregnancy. Thus,
while the true rate for recurrence may not
be completely evident, studies have dem-
onstrated a range from 1% to 17%, with
most studies citing an incidence of at least
10%.42,43
Although a history of prior
shoulder dystocia is not an absolute
contraindication to subsequent vaginal
delivery, these patients must be evaluated
carefully, taking into account patient
autonomy, prior pregnancy history, and
792 Ouzounian
www.clinicalobgyn.com
Copyright r 2016 Wolters Kluwer Health, Inc. All rights reserved.

3. future reproductive plans, and providing
thorough informed consent counseling
before delivery.
Other purported obstetric risk factors
for shoulder dystocia include excessive
maternal weight or weight gain, operative
vaginal delivery, oxytocin use, multipar-
ity, epidural use, and abnormal labor.1
Most of these factors may lead to or
actually result from excess fetal weight.
Moreover, while many of them have been
described in conjunction with shoulder
dystocia, that association cannot be
equated as a causative link. For example,
the rate of epidural use for pain relief in
labor continues to increase in the United
States, but the rate of shoulder dystocia
has remained essentially constant. Equally
important, recent studies that have ana-
lyzed these risk factors alone or in com-
bination have shown that they are poor
predictors for the occurrence of shoulder
dystocia.44,45
For example, in a 2005
study of over 1600 cases of shoulder
dystocia, Ouzounian and Gherman45
showed that the clinical triad of labor
induction, oxytocin use, and birthweight
greater than 4500 g had a sensitivity and
positive predictive value of 12.4% and
3.4%, respectively, for the occurrence of
shoulder dystocia.
For the most part, shoulder dystocia
remains an unpredictable and unprevent-
able event. Although prophylactic cesar-
ean section to avoid shoulder dystocia
may be an option in some cases, policies
of planned cesarean section for suspected
macrosomia have not been practical, and
can result in unnecessary cost as well as
increased maternal morbidity.46
Patients
with one or more risk factors should be
counseled, monitored and managed care-
fully, however, to maximize maternal and
neonatal outcomes.
References
1. Gherman RB, Chauhan S, Ouzounian JG, et al.
Shoulder dystocia: the unpreventable obstetric
emergency with empiric management guidelines.
Am J Obstet Gynecol. 2006;195:657–672.
2. Ouzounian JG, Korst LM, Sanchez M, et al.
Clinical risk factors do not predict shoulder
dystocia. J Reprod Med. 2016. (In press).
3. Soni AL, Mir NA, Kishan J, et al. Brachial
plexus injuries in babies born in hospital: an
appraisal of risk factors in a developing country.
Ann Trop Paediatr. 1985;5:69–71.
4. Jennett RJ, Tarby TJ, Kreinick CJ. Brachial
plexus palsy: an old problem revisited. Am J
Obstet Gynecol. 1992;166:1673–1676. Discussion
1676–1677.
5. Nocon JJ, McKenzie DK, Thomas LJ, et al.
Shoulder dystocia: an analysis of risks and
obstetric maneuvers. Am J Obstet Gynecol.
1993;168:1732–1737. Discussion 1737–1739].
6. Gonen R, Spiegel D, Abend M. Is macrosomia
predictable, and are shoulder dystocia and birth
trauma preventable? Obstet Gynecol. 1996;88:
526–529.
7. Bahar AM. Risk factors and fetal outcome in
cases of shoulder dystocia compared with normal
deliveries of a similar birth-weight. Br J Obstet
Gynaecol. 1996;103:868–872.
8. Gherman RB, Goodwin TM, Ouzounian JG,
et al. Brachial plexus palsy associated with
cesarean section: an in utero injury? Am J Obstet
Gynecol. 1997;177:1162–1164.
9. Ecker JL, Greenberg JA, Norwitz ER, et al. Birth
weight as a predictor of brachial plexus injury.
Obstet Gynecol. 1997;89:643–647.
10. Gherman RB, Ouzounian JG, Goodwin TM.
Obstetric maneuvers for shoulder dystocia and
associated fetal morbidity. Am J Obstet Gynecol.
1998;178:1126–1130.
11. Draycott TJ, Crofts JF, Ash JP, et al. Improving
neonatal outcome through practical shoulder
dystocia training. Obstet Gynecol. 2008;112:
14–20.
12. Foad SL, Mehlman CT, Ying J. The epidemiol-
ogy of neonatal brachial plexus palsy in the
United States. J Bone Joint Surg Am. 2008;90:
1258–1264.
13. Melendez J, Bhatia R, Callis L, et al. Severe
shoulder dystocia leading to neonatal injury: a
case control study. Arch Gynecol Obstet. 2009;
279:47–51.
14. Grobman WA, Miller D, Burke C, et al. Out-
comes associated with introduction of a shoulder
dystocia protocol. Am J Obstet Gynecol. 2011;
205:513–517.
15. Inglis SR, Feier N, Chetiyaar JB, et al. Effects of
shoulder dystocia training on the incidence of
brachial plexus injury. Am J Obstet Gynecol.
2011;204:e1–e6.
16. Walsh JM, Kandamany N, Ni Shuibhne N, et al.
Neonatal brachial plexus injury: comparison of
Shoulder Dystocia 793
www.clinicalobgyn.com
Copyright r 2016 Wolters Kluwer Health, Inc. All rights reserved.

4. incidence and antecedents between 2 decades. Am
J Obstet Gynecol. 2011;204:e1–e6.
17. Paris AE, Greenberg JA, Ecker JL, et al. Is an
episiotomy necessary with a shoulder dystocia?
Am J Obstet Gynecol. 2011;205:e1–e3.
18. Ouzounian JG, Korst LM, Miller DA, et al.
Brachial plexus palsy and shoulder dystocia:
obstetric risk factors remain elusive. Am J Peri-
natol. 2013;30:303–307.
19. Tsur A, Sergienko R, Wiznitzer A, et al. Critical
analysis of risk factors for shoulder dystocia.
Arch Gynecol Obstet. 2012;285:1225–1229.
20. Overland EA, Vatten LJ, Eskild A. Risk of
shoulder dystocia: associations with parity and
offspring birthweight. A popu-lation study of
1,914,544 deliveries. Acta Obstet Gynecol Scand.
2012;91:483–488.
21. Turrentine MA, Ramirez MM. Adverse perinatal
events and subsequent cesarean rate. Obstet
Gynecol. 1999;94:185–188.
22. Olugbile A, Mascarenhas L. Review of shoulder
dystocia at the Birmingham Women’s Hospital.
J Obstet Gynaecol. 2000;20:267–270.
23. Kees S, Margalit V, Schiff E, et al. Features of
shoulder dystocia in a busy obstetric unit.
J Reprod Med. 2001;46:583–588.
24. Gudmundsson S, Henningsson AC, Lindqvist P.
Correlation of birth injury with maternal height
and birthweight. BJOG. 2005;112:764–767.
25. Mollberg M, Hagberg H, Bager B, et al. High
birthweight and shoulder dystocia: the strongest
risk factors for obstetrical brachial plexus palsy
in a Swedish population-based study. Acta Obstet
Gynecol Scand. 2005;84:654–659.
26. Gurewitsch ED, Johnson E, Hamzehzadeh S,
et al. Risk factors for brachial plexus injury with
and without shoulder dystocia. Am J Obstet
Gynecol. 2006;194:486–492.
27. MacKenzie IZ, Shah M, Lean K, et al. Manage-
ment of shoulder dystocia: trends in incidence
and maternal and neonatal morbidity. Obstet
Gynecol. 2007;110:1059–1068.
28. Ford AA, Bateman BT, Simpson LL, et al.
Nationwide data confirms absence of ‘‘July phe-
nomenon’’ in obstetrics: it’ssafe to deliver in July.
J Perinatol. 2007;27:73–76.
29. Backe B, Magnussen EB, Johansen OJ, et al.
Obstetric brachial plexus palsy: a birth injury not
explained by the known risk factors. Acta Obstet
Gynecol Scand. 2008;87:1027–1032.
30. Acker DB, Sachs BP, Friedman EA. Risk factors
for shoulder dystocia. Obstet Gynecol. 1985;66:
762–768.
31. Stotland NE, Caughey AB, Breed EM, et al. Risk
factors and obstetric complications associated
with macrosomia. Int J Gynaecol Obstet. 2004;
87:200–206.
32. Dudley NJ. A systematic review of the ultra-
sound estimation of fetal weight. Ultrasound
Obstet Gynecol. 2005;25:80–89.
33. American College of Obstetricians and Gynecol-
ogists. Practice Bulletin 134, Intrauterine Growth
Restriction. Washington DC: Lippincott & Wil-
liams; 2013.
34. American College of Obstetricians and Gynecol-
ogists. Practice Bulletin 40, Shoulder Dystocia.
Washington DC: Lippincott & Williams; 2010.
35. Langer O, Berkus MD, Huff RW, et al. Shoulder
dystocia: should the fetus weighing greater than
or equal to 4000 grams be delivered by cesarean
section? Am J Obstet Gynecol. 1991;165:831–837.
36. Cohen B, Penning S, Major C, et al. Sonographic
prediction of shoulder dystocia in infants of
diabetic mothers. Obstet Gynecol. 1996;88:10–13.
37. Cohen BF, Penning S, Ansley D, et al. The
incidence and severity of shoulder dystocia cor-
relates with a songraphic measurement of asym-
metry in patients with diabetes. Am J Perinatol.
1999;16:197–201.
38. Modanlou HD, Komatsu G, Dorchester W, et al.
Large-for-gestational age neonates; anthropo-
metric rea-sons for shoulder dystocia. Obstet
Gynecol. 1982;60:417–423.
39. McFarland MB, Trylovich CG, Langer O.
Anthropometric differences in macrosomic in-
fants of diabetic and nondiabetic mothers.
J Maternal Fetal Med. 1998;7:292–295.
40. Casey BM, Lucas MJ, Mcintire DD, et al. Preg-
nancy outcomes in women with gestational dia-
betes compared with the general obstetric
population. Obstet Gynecol. 1997;90:869–873.
41. Keller JD, Lopez-Zeno JA, Dooley SL, et al.
Shoulder dystocia and birth trauma in gesta-
tional diabetes: a five-year experience. Am J
Obstet Gynecol. 1991;165:928–930.
42. Bingham J, Chauhan SP, Hayes E, et al. Recur-
rent shoulder dystocia: A review. Obstet Gynecol
Surv. 2010;65:183–188.
43. Ouzounian JG, Gherman RB, Chauhan S, et al.
Recurrent shoulder dystocia: analysis of inci-
dence and risk factors. Am J Perinatol. 2012;29:
515–518.
44. Revicky V, Mukhopadhyay S, Morris EP, et al.
Can we predict shoulder dystocia? Arch Gynecol
Obstet. 2012;285:291–295.
45. Ouzounian JG, Gherman RB. Shoulder dystocia:
are historic risk factors reliable predictors? Am J
Obstet Gynecol. 2005;192:1933–1938.
46. Rouse DJ, Sonography Owen J. suspected macro-
somia, and prophylactic cesarean: a limited part-
nership. Clin Obstet Gynecol. 2000;43:326–334.
794 Ouzounian
www.clinicalobgyn.com
Copyright r 2016 Wolters Kluwer Health, Inc. All rights reserved.