Shoulder Dystocia 

First described in 1730, shoulder dystocia is an uncommon obstetric complication of cephalic vaginal deliveries whereby the fetal shoulders do not deliver as they would routinely after the head has emerged from the mother’s introitus. This occurs when one or both shoulders become impacted against the bones of the maternal pelvis.^[1]

Since this phenomenon depends on a relative size and/or positional discrepancy between the fetal and pelvic bony dimensions, the at-risk patients are nearly always parturients undergoing cephalic vaginal delivery after 34 weeks’ gestation.

The reason shoulder dystocia occurs is a mechanical one.^{[2, 3]} During the fetal head’s cardinal movements of descent, flexion, and internal rotation within the bony pelvis, the shoulders descend to reach the pelvic inlet. During the head’s subsequent extension, delivery, and external rotation, prior to final expulsion, the shoulders need to rotate within the bony pelvis in a winding fashion to end in the most accommodating dimension of the pelvis, its oblique diameter. If either the fetal shoulder dimensions are too large or the maternal pelvis is too narrow to permit shoulder rotation to the oblique pelvic diameter, or both, persistent anterior-posterior orientation of the fetal shoulders may result in the anterior shoulder being obstructed behind the symphysis pubis, impeding delivery. This leads to shoulder dystocia. If the sacral promontory also obstructs the posterior shoulder, bilateral (and more difficult) shoulder dystocia occurs.

Antepartum risk factors for shoulder dystocia are listed below in order of importance:

• History of shoulder dystocia in a prior vaginal delivery^[4]
• Fetal macrosomia (having a disproportionately large body compared to head)^[5]
• Diabetes/impaired glucose tolerance (false positive glucose challenge test)^[6]
• Excessive weight gain (>35 lb) during pregnancy^[7]
• Obesity (body mass index >25)^[5]
• Postterm pregnancy^[6]

Intrapartum risk factors are as follows:

• Precipitous second stage (< 20 min)^[6]
• Operative vaginal delivery (vacuum, forceps, or both)^[5]
• Prolonged second stage^[5]

  • Without regional anesthesia (>2 h for nulliparous patients, or > h for multiparous patients)
  • With regional anesthesia (>3 h for nulliparous patient, >2 h for others)
• Induction of labor for impending macrosomia^[8]

In spite of these risk factors, shoulder dystocia is impossible to predict in a specific patient because many patients with multiple risk factors will not experience it, whereas many shoulder dystocia events will occur in patients with no risk factors, including even patients who experience severe shoulder dystocia delivering a small-for-gestational-age infant.^[9] The reason for this is that the condition is caused by a dynamic or evolving mechanical event, rather than by the presence of a specific preexisting or intrapartum clinical risk factor or use of a particular intervention.

Although shoulder dystocia is impossible to predict or prevent in a individual patient, it has recently been shown prospectively that the incidence of shoulder dystocia can be reduced in a population by diagnosing and treating mild gestational diabetes mellitus (defined as 2 or more abnormal values after a 3-hour 100g oral glucose-tolerance test, but with a glucose fasting level < 95 mg per deciliter). Treating these patients with self-monitoring of blood glucose, diet, and insulin therapy as needed results in a significant decrease in large-for-gestational-age (LGA) infants, cesarean sections, and shoulder dystocia (by 60%).^[10]

Considered an obstetric emergency, shoulder dystocia can result in significant fetal and maternal harm if not resolved in a competent and expedient manner. A 6-minute head-to-body interval has been demonstrated to be safe.^[11] Beyond that time, there is increased risk of neonatal depression, acidosis, asphyxia, central nervous system damage, or even death.^{[12, 13, 14]}

Incidence

Although the incidence range promulgated by ACOG is 0.6-1.4%, the incidence of shoulder dystocia varies in the literature by a factor of 50, from 1 in 750 to 1 in 15 deliveries.^{[15, 16, 17]} One reason for this wide variation is in part the variation in denominator or specific patient population (eg, all births vs only vaginal births vs only term vaginal births) used to calculate incidence. However, the primary reasons for incidence variation are difficulty in diagnosis (see Diagnosis below) and underreporting because the condition is most often mild and resolved without untoward outcome.

Based on a host of retrospective studies, most incidence ranges vary from 1-2% of cephalic vaginal deliveries. Although few in number, prospective studies examining shoulder dystocia incidence among vaginal deliveries generally report higher values, from 3.3-7%.^{[14, 16, 18, 19, 20]} These higher values among 2100 vaginal cephalic deliveries within the few prospective studies likely reflect the more accurate incidence among the at-risk population (vaginal, cephalic deliveries of at least 34 weeks’ gestation).

Diagnosis

The 2 principal reasons for the wide variation in incidence are as follows:

1. There is no objective diagnosis for shoulder dystocia.^[21]
2. Milder forms of the condition are difficult to diagnose, or are often uneventful and uncoded.^{[22, 23]}

Although the textbook definition is clear, the obstetric provider cannot visualize the obstruction clinically. Two commonly accepted diagnoses are as follows:

1. More than customary traction needed to deliver the fetal trunk^[1]
2. The need to perform ancillary maneuvers to complete delivery^{[15, 24]}

Since “customary traction” varies from clinician to clinician, the diagnosis is inherently subjective (see following video).

In high volume practices, for example, shoulder dystocia is not consistently coded because it is uneventful.^[17] One objective clinical indication that occurs in a minority of shoulder dystocia deliveries is known as the turtle sign, where the fetal head, after it delivers, retracts against the perineum, as shown in the following image.

Fundal pressure should not be used in attempts to overcome or treat shoulder dystocia, as its use is actually counterproductive. The reason for this is that pressure directed from behind the fetus only further impacts the anterior shoulder, making the shoulder dystocia more difficult to resolve and thereby increasing the risk of permanent brachial plexus injury.^{[25, 26]}

Strong lateral traction (more than 20 pounds – 2 to >4 times the traction typically utilized in routine delivery) should also be avoided, as increased lateral traction increases the risk of both transient and permanent brachial plexus injury.{Ref9}^[26] The greater the traction, the greater the severity of brachial plexus injury.^[27]

Finally, head rotation beyond 90 degrees is to be avoided, because it increases the risk of transient and permanent brachial injury.^[28]

Because of the time constraints during shoulder dystocia, anesthetic considerations have a limited role. The rare exception would be if cephalic replacement is necessary, when uterine relaxants such as intravenous nitroglycerine or halogenated inhalational agents should be administered to decrease the risk of uterine rupture from the procedure.

When an obstetric provider diagnoses shoulder dystocia, no specialized equipment is required. Only obstetric skill and team coordination are needed at this point.

Management of shoulder dystocia primarily involves repositioning the laboring patient or repositioning the fetus. These are discussed in detail in the Technique section.

Proper management of shoulder dystocia is the key to solving the impaction problem without untoward outcome. About a dozen techniques can be broadly divided into 2 categories–fetal maneuvers (where the manipulation is directly upon the fetus within the birth canal) and maternal maneuvers (where the primary manipulation is on the mother–often done by ancillary personnel). These 2 categories of shoulder dystocia maneuvers are listed below.

Table #1. Shoulder dystocia maneuvers (Open Table in a new window)

Episiotomy is not listed as a maneuver in its own right, because it offers no mechanical and no clinical benefit to resolve the shoulder dystocia when fetal maneuvers are not used. Recent research has demonstrated that episiotomy does not decrease risk of brachial plexus injury and increases the risk of perineal trauma.^{[39, 40]} The only reason to perform an episiotomy after a shoulder dystocia is diagnosed is to eliminate soft tissue resistance that is interfering with the ability to insert the whole hand into the hollow of the sacrum posteriorly in order to perform fetal maneuvers.

Five maneuvers (Rubin, Jacquemier, Woods, and McRoberts maneuvers, and suprapubic pressure), either singly or in combination, accomplish delivery nearly 100% of the time. The others are used less commonly or resorted to only after primary ones have not accomplished delivery. Each of the main 5 is briefly described below. Recent research has demonstrated there are fewer brachial plexus injuries when fetal maneuvers are employed as the initial maneuver.^{[41, 42, 43]} Therefore, we begin with the more effective fetal maneuvers:^{[44, 45, 46, 47, 48]}

Rubin maneuver

The Rubin maneuver (see image below) involves inserting one hand in the birth canal posteriorly or anteriorly, on the dorsal aspect of the fetal shoulders and rotating the shoulder inward (adduction) about 30° such that the shoulders come to lie in the oblique diameter of the pelvis.

By applying pressure to the dorsal aspect of the shoulder, the rotation itself adducts the fetal shoulders, thereby reducing their bisacromial diameter. The principal effect of this is to increase the clearance between the shoulders and the pelvis by about 20 mm.^[2] Another advantage of this method is the ability for the clinician to know the correct orientation of the shoulders, especially when the head emerges in direct occipitoanterior and fails to restitute spontaneously as a result of tight retraction against the perineum (turtle sign), or restitutes incompletely leaving some uncertainty about the relative head-shoulder position. Ensuring the correct orientation of the shoulders avoids the injury producing rotation of the head beyond 90°. If the Rubin's rotation can be accomplished, the anterior shoulder should emerge from below the symphysis with little or no additional traction required. Research has demonstrated that using rotation as an initial maneuver in an attempttoresolveshoulderdystocia decreases the risk of brachial plexus injury.^{[40, 43]}

Posterior arm delivery (Jacquemier maneuver)

Depicted in the image below, the clinician’s hand (including the thumb) is inserted in the birth canal in an effort to deliver the posterior arm (not just the shoulder) first. (When the left shoulder is anterior, the operator’s right hand is used; if the right shoulder is anterior, the operator’s left hand is used). Sliding the hand along the dorsal aspect of the humerus and pressing it against the fetal chest, the clinician then palpates the elbow. If the elbow is already flexed, the operator’s hand grasps the fetal forearm and wrist and sweeps the forearm over the chest and across the infant’s face, extending the arm at the elbow and shoulder to deliver it first.

Movements should be directed only medially toward and then across the fetal chest, supporting and continually pressing the humerus against the chest to avoid possible humeral fracture from attempting to flex it laterally against resistance from the vaginal sidewall.

If the elbow is extended, making the forearm difficult to reach and deliver, the operator should attempt to flex it by applying finger pressure to the dorsal aspect of the forearm, and, if needed, simultaneously pressing on the ventral aspect of the elbow crease to cause it to bend. After flexion of the elbow, the operator grasps and sweeps the forearm and wrist as described above. If the elbow will not flex, the operator should continue directly into Woods screw maneuver (see below). Once the posterior arm is delivered, the fetal trunk almost always follows because of the additional 20 mm of clearance.^[46] If not, the delivered arm can be used to help rotate the trunk (as in Woods screw) so that the remaining anterior shoulder is brought to occupy the oblique plane of the pelvis, anterior to the pubic symphysis.

Woods screw maneuver

The Woods screw maneuver (see following video) is an extension of the posterior Rubin maneuver. At least a 180° rotation of the fetal trunk is achieved using pressure on the dorsal aspect of the posterior shoulder to help adduct the shoulders. The rotation is skew rather than planar and directed toward the operator (ie, caudad relative to the mother). The winding motion, similar to the way a screw advances by turning it, thus furthers the descent and expulsion of the trunk of the fetus. This 180° rotation is usually successful at delivering the trunk. If not, the rotation and forward motion is repeated. Care should be used here to rotate inward toward the opposite shoulder (ie, achieving shoulder adduction) as the opposite rotation necessarily abducts the fetal shoulders, thereby increasing the bisacromial diameter. This is a modification of the original Woods maneuver that had employed abduction and simultaneous application of fundal pressure, both of which are counterproductiveowingtothebiomechanical considerations discussed previously.

Because the intent is to rotate 180°, the clinician should use the left hand when the fetus’ right shoulder is anterior and the right hand for a left anterior shoulder. Although initially awkward and counterintuitive, this allows the clinician’s arm to sweep in a natural direction that supinates his/her arm without having to substitute the opposite hand mid procedure.

McRoberts maneuver

The de facto first line of treatment for shoulder dystocia in the United States is McRoberts maneuver (see image below), in which 2 assistants hyperflex the mother’s thighs against her abdomen.^[15] By doing so, the symphysis pubis is raised about 9 mm, which may provide sufficient clearance to release the anterior shoulder from behind the symphysis.^[46] By flattening the lumbosacral spine, McRoberts positioning may also advance the posterior fetal shoulder into the hollow of the sacrum.^[44]

McRoberts’ maneuver alone resolves up to 50% of shoulder dystocia deliveries with little or no additional traction required.^[45] Providers must maintain conscious awareness of the natural tendency to increase traction in this circumstance. Care should be taken to limit the traction to, at most, moderate, and avoid repeated or extended attempts. Failure to resolve shoulder dystocia at this point should prompt progression to additional maneuvers. McRoberts’ positioning can be continued^[44] during the performance of additional maneuvers as it improves operator access to the posterior shoulder for these maneuvers.

Suprapubic pressure

Suprapubic pressure (see image below) is a maneuver performed usually by a nurse who applies stout directional (45° downward) pressure to the maternal abdomen just above the pubic symphysis. This pressure should be applied to the posterior aspect of the anterior shoulder pushing toward the opposite side from where the attendant is positioned as shown. The effects of this are 2-fold: (1) to compress soft tissue that may be making the impaction worse and (2) to help rotate the anterior shoulder away from the symphysis pubis and into the diagonal conjugate of the maternal pelvis.

Suprapubic pressure is often used concomitantly with McRoberts maneuver. Since both maneuvers ultimately rely on clinician traction to the head to accomplish delivery of the fetal trunk, the same caution in applying traction following suprapubic pressure should be observed as when following McRoberts maneuver. If and when suprapubic pressure is used to assist an operator’s manual rotation of the fetal shoulders (as in Woods screw or Rubin maneuver), then the direction of the suprapubic pressure should be reversed to encourage rotation of the anterior shoulder in the same rotational direction (clockwise or counterclockwise as determined by initial fetal shoulder position) as the operator is guiding the posterior shoulder.

• Insert fingers prior to attempting delivery to ensure proper assessment of the shoulder orientation.
• Use fetal maneuvers as the initial management of some shoulder dystocia deliveries to become adroit and remain competent and facile at them.
• During McRoberts maneuver, suprapubic pressure, or both, keep traction to the head limited in magnitude and directed axially as much as possible.
• Avoid repeating attempts at traction, as they are likely to increase in magnitude and increase the risk for brachial plexus injury.
• Be aware that McRoberts maneuver and suprapubic pressure are less effective in patients who are obese because of additional soft tissue preventing full abduction of the thighs against the abdomen and transmission of pressure applied by ancillary personnel to the anterior shoulder.
• Unless room is needed posteriorly to perform fetal maneuvers, an episiotomy is not needed and is potentially damaging to the patient’s perineum.
• As part of training and continuing medical education, conduct shoulder dystocia simulations to assess and improve communication, documentation, and most importantly, clinical management. Practitioners trained with shoulder dystocia simulation drills experience better clinical outcomes and fewer shoulder dystocia-associated injuries after training than before.^{[49, 43]}

Complications from shoulder dystocia are many. Maternally, postpartum hemorrhage can result from uterine atony caused either by overdistention from fetal macrosomia and/or dysfunctional contractility caused by mechanical obstruction. Another complication is third or fourth degree perineal laceration or extension of episiotomy. Since episiotomy is not necessary for most shoulder dystocia deliveries, this complication may be avoidable; however, fetal size alone may cause these extensive lacerations. Although immediately reparable in the delivery room, potential long-term maternal consequences include wound breakdown, fistula formation, dyspareunia, and fecal incontinence.

Although not uncommon among deliveries without shoulder dystocia, neonatal clavicle fracture, when it occurs following shoulder dystocia, is most often not preventable because the compression of the acromial aspect of the shoulder from the symphysis pubis. Some clavicle fractures can result from direct downward application of suprapubic pressure; however, this often resolves the shoulder dystocia and is therefore useful. Fortunately, a clavicle fracture complication usually resolves without intervention within the neonatal period.

One complication of a posterior arm delivery is a fractured humerus, which can occur if the operator forces the arm against resistance encountered in sweeping the arm. This too may be unavoidable in successful resolution of shoulder dystocia. Humeral fractures are treated with immobilization and also generally heal within the neonatal period.

Brachial plexus injury to the newborn is the most notorious complication of shoulder dystocia. Most of these injuries resolve before discharge from the hospital; however, some last longer and some are permanent and cause varying levels of limited motion of the affected upper extremity depending on the nature and extent of the injury. Since this injury is caused by deviation and/or rotation of the fetal head from the shoulder, the best way to reduce the likelihood of this complication is by using, at most, moderate traction on the head during maternal maneuvers. To the extent possible, traction should be directed in line with the axis of the fetal spine. Axial traction poses much less risk to the brachial plexus than lateral (downward or upward) traction^[2] As residents are more likely to experience shoulder dystocia-related brachial plexus injury^[41] , simulation training can provide experience in shoulder dystocia management, which results in improved clinical outcome withfeweradverseoutcomes.^{[49, 43]}

Although rare, one devastating complication of catastrophic shoulder dystocia is neonatal hypoxic ischemic encephalopathy and/or death. The mechanism for oxygen deprivation is usually attributed to variable compression of the umbilical cord within the birth canal during the obstructed delivery. To help prevent this complication, especially in the presence of a nuchal cord (even when nonreducible), the delivering clinician should never clamp and sever the cord until at least the anterior shoulder has been successfully delivered.

One other neonatal complication from shoulder dystocia is sudden fetal circulatory collapse that can result from a precipitous drop in neonatal blood pressure following delivery. This can occur with the sudden release of the partial (venous greater than arterial) compression of the umbilical cord immediately upon delivery. If unrecognized as a cause, improper resuscitation may lead to asphyxia or death. Pediatricians in attendance should consider volume resuscitation when a fetus is suddenly more depressed or born with no heart rate immediately following shoulder dystocia.^[50]