Shoulder Dystocia

Shoulder dystocia was first described in 1730 and is an obstetric complication of cephalic vaginal deliveries during which the fetal shoulders do not deliver after the head has emerged from the mother’s introitus. It occurs when one or both shoulders become(s) impacted against the bones of the maternal pelvis (symphysis pubis and possibly the sacral promontory), as shown in the image below. ^[1]

Since this phenomenon occurs because of a relative size or positional discrepancy between the fetal and pelvic bony dimensions, it nearly always occurs in parturients undergoing cephalic vaginal delivery after 34 weeks’ gestation.

Shoulder dystocia occurs for mechanical reasons. ^{[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 arrive in the most accommodating dimension of the pelvic outlet, its oblique diameter. If either the fetal shoulder dimensions are too large or the maternal pelvis is too narrow, or both, to permit shoulder rotation to the oblique pelvic diameter, persistent anteroposterior orientation of the fetal shoulders may result in the anterior shoulder being obstructed behind the symphysis pubis impeding delivery and leading to shoulder dystocia. If the sacral promontory also obstructs the posterior shoulder, bilateral (and more difficult) shoulder dystocia occurs.

Direct antenatal risk factors for shoulder dystocia are listed below in order from greatest to least risk:

• 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]

Risk factors for macrosomia, which are indirect markers for shoulder dystocia, are delineated below:

• Excessive weight gain (>35 lb) during pregnancy ^[7]

• Maternal obesity (body mass index >30 kg/m²) ^{[7, 8]}

• Asymmetric accelerated fetal growth in nondiabetic patients ^[9]

• Postterm pregnancy ^[6]

• Parity ^[10]

Intrapartum risk factors are as follows:

• Precipitous second stage (< 20 min) ^{[11, 12]}

• Operative vaginal delivery (vacuum, forceps, or both) ^[5]

• Prolonged second stage ^[5]

  • Without regional anesthesia (>2 h for nulliparous patients, or >1 h for multiparous patients)

  • With regional anesthesia (>3 h for nulliparous patient, >2 h for others)

• Induction of labor for impending macrosomia ^{[13, 14]}

As a preventive measure, induction of labor for impending macrosomia does not decrease shoulder dystocia incidence. ^[13] Despite these well-defined risk factors, shoulder dystocia is impossible to predict before delivery of the head because most patients with multiple risk factors do not experience it, and many shoulder dystocia deliveries occur in patients with no risk factors. ^{[14, 15]}  Third trimester ultrasound screening that indicated a higher estimated fetal weight (>4000 g) had only 22% sensitivity in predicting shoulder dystocia. ^[16] Severe shoulder dystocia can occur during delivery of a small-for-gestational-age infant. ^[17] The poor predictability relates to shoulder dystocia being caused by a dynamic and evolving mechanical event, rather than by simply the presence of specific antenatal or intrapartum clinical risk factors.

Although shoulder dystocia is virtually impossible to predict or prevent in an individual patient, it has 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 100-g oral glucose-tolerance test, but with a glucose fasting level < 95 mg/dL). Treating these patients with self-monitoring of blood glucose, diet, and insulin therapy, as needed, resulted in a significant decrease in large-for-gestational-age (LGA) infants, cesarean deliveries, and shoulder dystocia (by 60%). ^[18]  Whether changing the criteria for diabetic diagnosis, thereby increasing the diabetic rate from 5% to 18% of pregnancies, is an overall effective management strategy or not, is under considerable obstetric debate. ^{[19, 20]}

In a prospective randomized trial, the incidence of shoulder dystocia was significantly reduced with a push-back maneuver in the final stages of the second stage. ^[21]  The push-back maneuver is a preventive obstetric maneuver that is performed gently on the fetal head, with the aim of helping the anterior shoulder slip behind the symphysis pubis, to give the shoulders more time to enter the pelvic cavity.

Considered an obstetric emergency, shoulder dystocia can result in significant fetal and maternal harm if not resolved in a competent and expedient manner. Cord pH drops with increasing head-to-body delivery interval, but the drop does not become clinically significant for about 5 minutes. ^{[22, 23]}  For an otherwise healthy fetus, a head-to-body delivery interval less than or equal to 6 minutes has been demonstrated not to be a risk factor for hypoxic ischemic encephalopathy (HIE). ^[24] Beyond that time, however, there is increased risk of neonatal depression, acidosis, asphyxia, central nervous system damage, and death. ^{[25, 26]}

Incidence

Shoulder dystocia incidence ranges cited by the American College of Obstetricians and Gynecologists (ACOG) and the Royal College of Obstetricians and Gynaecologists (RCOG) are 0.2%-3.0% and 0.58-0.70%, respectively. ^{[27, 28]}  However, the incidence of clinically diagnosed shoulder dystocia varies in the literature by a factor of 30, from 1 in 769 vaginal to 1 in 25 deliveries. ^{[29, 30]} One reason for this wide variation is, in part, the variation in the denominator (eg, all births vs only vaginal births vs only term vaginal births) used to calculate incidence. However, the primary reasons for the variation are (1) difficulty in diagnosis (see diagnosis below) and (2) time to diagnosis.

Based on a host of retrospective studies, most cited incidences range from 0.5-3% of deliveries. ^[31] Although few in number, prospective studies examining shoulder dystocia incidence among vaginal deliveries in the United States generally report higher values, from 3.4-7.0%. ^{[30, 32, 33, 34, 35]}  These higher values among more than 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) with the current standard of care in most places.

Diagnosis

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

• There are no objective standardized diagnostic criteria for shoulder dystocia. ^[36]

• Milder forms of the condition are difficult to diagnose, or are uneventful and sometimes not recognized or coded or both. ^{[37, 38]}

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

1. More than customary traction needed to deliver the fetal trunk. ^[39]

2.  Shoulder dystocia is the inability to deliver shoulders with gentle downward traction on the head, requiring additional maneuvers to effectuate delivery. ^[27]

3. A head to body interval longer than 60 seconds. ^[30]

While the majority of shoulder dystocia deliveries do take longer that 60 seconds to resolve, a sizeable minority do not. ^{[32, 35, 40]}  Since "customary traction" varies from clinician to clinician, the diagnosis is inherently subjective (as demonstrated in the following video).

In locations where the standard of care is to wait for a contraction before attempting delivery of the trunk in all vaginal deliveries, the incidence of shoulder dystocia is well below 1%. ^{[41, 42, 43]} While waiting for a contraction after the head has delivered increases the head-to-body interval, there is no significant risk of neonatal depression, neonatal acidosis, or birth asphyxia. ^{[23, 44]}

In high-volume practices, shoulder dystocia is not consistently coded when it is uneventful. ^[29] 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. The turtle sign may also occur in non–shoulder dystocia deliveries. 

Fundal pressure should not be used in the management of shoulder dystocia, as it is counterproductive. Pressure directed from behind the fetus only further impacts the anterior shoulder, making the shoulder dystocia more difficult to resolve and increasing the risk of brachial plexus injury. ^{[45, 46]}

Strong lateral traction (more than 20 lb, which is more than 4 times the traction typically used in routine delivery) should also be avoided, as increased lateral traction increases the risk of both transient and permanent brachial plexus injury. ^{[32, 46, 47]}  The greater the traction, the greater the severity of brachial plexus injury. ^{[48, 49]}

Finally, head rotation beyond 90°, as shown in the image below, is to be avoided because it increases the risk of neck and brachial plexus injury. ^[50]

Because of the time constraints during shoulder dystocia, anesthesia normally has a limited role. If cephalic replacement is necessary, uterine relaxants such as intravenous nitroglycerine or halogenated inhalational agents should be administered to decrease the risk of uterine rupture.

No specialized equipment is required. Obstetric skill, team coordination, and detailed documentation are essential.

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

Proper management of shoulder dystocia is critical to avoid untoward outcomes. About a dozen techniques can be broadly divided into two categories: fetal maneuvers (during which the manipulation is directly upon the fetus) and maternal maneuvers (during which the primary manipulation is on the mother, often done by ancillary personnel). See the Table below.

         Table. Shoulder Dystocia Maneuvers (Open Table in a new window)

Episiotomy is not listed as a separate maneuver because it offers no mechanical or clinical benefit when fetal maneuvers are not used. Studies have demonstrated that episiotomy does not decrease risk of brachial plexus injury and increases the risk of perineal trauma. ^{[60, 61, 62]} The only reason to perform an episiotomy in the setting of shoulder dystocia is to eliminate soft tissue resistance that is interfering with the ability to insert the whole hand into the hollow of the sacrum posteriorly to perform fetal maneuvers.

Six maneuvers (Rubin, posterior arm, shoulder shrug, Woods, and McRoberts maneuvers, and suprapubic pressure), either singly or in combination, accomplish delivery nearly 100% of the time. The Gaskin maneuver is primarily used by midwives; although effective, obstetricians have not generally adopted it, in part due to the overwhelming use of epidural anesthesia in the United States. The others are used less commonly or resorted to only after primary ones have failed. Multiple research studies have demonstrated there are fewer brachial plexus injuries when fetal maneuvers are used initially. ^{[45, 63, 64, 47]}  The reason for this is because fetal maneuvers are mechanically superior to maternal maneuvers. ^{[3, 65, 66]}

Prior to initiating any maneuvers, once shoulder dystocia is suspected, it is essential to assess shoulder orientation. Using the protocol below has been shown to reduce untoward outcomes associated with shoulder dystocia. ^[64]

Rubin maneuver

The Rubin maneuver involves inserting one hand in the vagina posteriorly or anteriorly along the dorsal aspect of the fetal shoulder and rotating the shoulder inward (adduction) about 30° until the shoulders lie in the oblique diameter of the pelvis.

By applying pressure to the dorsal aspect of the shoulder, the pressure adducts the fetal shoulders, thereby reducing the bisacromial diameter. Along with a rotation, this increases the clearance between the shoulders and the pelvis by about 20 mm. ^[65] Another advantage is that it ensures the clinician knows the correct orientation of the shoulders, which is not always obvious. Ensuring the correct orientation of the shoulders avoids the rotation of the head beyond 90°, which can cause fetal injury. If the Rubin rotation can be accomplished, the anterior shoulder should emerge from below the symphysis with little or no additional traction. Using rotation as an initial maneuver decreases brachial plexus stetch and the risk of brachial plexus injury. ^{[64, 66]}

See the image below.

Posterior arm delivery (Jacquemier maneuver)

In this maneuver, the clinician’s hand (including the thumb) is inserted in the vagina 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 must be 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 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 humerus fracture from attempting to flex it laterally against the vaginal sidewall.

See the image below.

If the elbow is extended, the forearm is difficult to reach and deliver. The operator should attempt to flex it by applying pressure with his or her finger to the dorsal aspect of the forearm and, if needed, simultaneously press 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 the Woods screw maneuver. Once the posterior arm is delivered, the fetal trunk almost always follows because of the additional 20 mm of clearance. ^[65]  If not, the delivered arm can be used to help rotate the trunk (as in the Woods screw maneuver) so that the remaining anterior shoulder is brought to occupy the oblique plane of the pelvis, anterior to the pubic symphysis.

If the posterior shoulder too far back to reach the arm, grab the shoulder and advance it into the hollow of the sacrum.  

Woods screw maneuver

The Woods screw maneuver is an extension of the posterior Rubin maneuver. The fetal trunk is rotated at least 180° 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. The winding motion, similar to the way a screw advances by turning it, 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, which used abduction and simultaneous application of fundal pressure, both of which are counterproductive.

Because the intent is to rotate 180°, the clinician should use the left hand when the fetus’s 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 the arm without having to substitute the opposite hand mid procedure.

See the video below.

Shoulder shrug maneuver

This maneuver is specifically geared toward severe shoulder dystocia, often when the posterior shoulder is back near the sacral promontory. The thumb and index finger are clamped around the posterior shoulder. Move the posterior shoulder forward into the hollow of the sacrum. Align  the head toward the body’s axis to form the head–shoulder unit and rotate this as a unit 180° in the direction of the chest. On rotation, the anterior shoulder has become posterior and has advanced in the pelvis. Delivery now proceeds with minimal forward traction and delivery of the neonate. ^[21]  Axillary traction has been used as the first internal maneuver for a large number of women, with a higher success rate than other internal maneuvers without increase in maternal or neonatal morbidity. ^[59]

McRoberts maneuver

The de facto first line of treatment for shoulder dystocia in the United States is McRoberts maneuver (see image below), in which two assistants hyperflex the mother’s thighs against her abdomen. ^[39]  This raises the symphysis pubis about 9 mm, which may provide sufficient clearance to release the anterior shoulder from behind the symphysis. ^[65] By flattening the lumbosacral spine, McRoberts positioning may also advance the posterior fetal shoulder into the hollow of the sacrum.

McRoberts maneuver alone resolves about 42% of shoulder dystocia deliveries with little additional traction required. ^[67] However, the introduction of the maneuver does not decrease the rate of injury if proper force training is not done. ^[68] Providers trained in using the maneuver itself raised awareness and diagnosis of shoulder dystocia; however, it did not decrease the rate of injury. ^[69]  Obstetric providers must maintain conscious awareness of the natural tendency to increase traction after McRoberts maneuver or suprapubic pressure is performed, or both are performed simultaneously. Care should be taken to limit to at most moderate traction and to avoid repeated or extended attempts. Failure to resolve shoulder dystocia at this point should prompt progression to fetal maneuvers. McRoberts positioning can be continued during the performance of additional maneuvers as it improves operator access to the posterior shoulder.

See the image below.

Suprapubic pressure

Suprapubic pressure is usually performed 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 nurse is positioned. The effects of this are 2-fold: (1) to help rotate the anterior shoulder away from the symphysis pubis and into the diagonal conjugate of the maternal pelvis, and (2) to compress soft tissue, which may be making the impaction more severe.

Suprapubic pressure is often used concomitantly with the 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 the McRoberts maneuver should be observed. When suprapubic pressure is used to assist manual rotation of the fetal shoulders (as in Woods screw or Rubin maneuver), then the direction of the suprapubic pressure should be directed 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.

See the image below.

As shown in the figure below, insert fingers prior to attempting delivery to ensure proper assessment of the shoulder orientation. This is good practice for all cephalic vaginal deliveries.

Wait for a contraction after suspecting a shoulder dystocia or observing a turtle sign. In most instances, the shoulders deliver spontaneously. The additional 1-2 minutes on the perineum does not increase the risk of neonatal depression, acidosis, or birth asphyxia.

Use fetal maneuvers early in the management of shoulder dystocia deliveries to become adroit and remain competent and facile with them.

During posterior arm delivery, insert your whole hand. Do not hold your inserting hand with the thumb away from the fingers. This not uncommon error makes it difficult or impossible to insert the entire hand into the vagina.

During the 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.

McRoberts maneuver and suprapubic pressure are less effective in patients who are obese because the additional soft tissue prevents full abduction of the thighs against the abdomen and limits 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, shoulder dystocia simulations should be conducted to assess and improve communication, documentation, and, most importantly, clinical management. Practitioners trained with effective shoulder dystocia simulation drills experience better clinical outcomes and fewer shoulder dystocia-associated injuries after training than before. ^{[70, 64, 71, 72, 73, 74]}  In one study, repeated shoulder dystocia training eliminated permanent brachial plexus injuries altogether. ^[75]

Standardized forms are helpful in clear and consistent documentation, and quality assurance. Use of a mandatory shoulder dystocia documentation form is associated with significant improvement in the comprehensiveness of delivering provider narrative notes and may encourage more complete and accurate charting. Such improvements can allow for more complete and accurate explanation of events to patients and better demonstrate adherence to standards of care in the management of shoulder dystocia. However, using forms does not necessarily improve outcomes without concomitant training. ^{[73, 76]}

There are many complications associated with shoulder dystocia. Postpartum hemorrhage can result from uterine atony caused by either overdistention from fetal macrosomia or dysfunctional contractility caused by mechanical obstruction. Third- or fourth-degree perineal laceration or episiotomy extension can also occur. Since episiotomy is not necessary for most shoulder dystocia deliveries, this complication may be avoidable. However, fetal size alone may cause these extensive lacerations. Potential long-term consequences include wound breakdown, fistula formation, dyspareunia, and fecal incontinence.

Neonatal clavicle fracture is associated with shoulder dystocia, although not uncommon among mechanically difficult deliveries or deliveries without recorded or recognized shoulder dystocia. ^[37] It is a recognized complication of shoulder dystocia and is most often not preventable because of the compression of the acromial aspect of the shoulder from the symphysis pubis or the posterior clavicle the sacral promontory. Some clavicle fractures can result from direct downward application of suprapubic pressure, but this often resolves the shoulder dystocia and is therefore useful. Fortunately, clavicle fracture usually resolves without intervention or sequelae within the neonatal period.

Fractured humerus can occur with a posterior arm delivery if the operator forces the arm against resistance encountered while sweeping it. This too may be unavoidable in successful resolution of shoulder dystocia. Humeral fractures are treated with immobilization and generally fully heal within the neonatal period.

Brachial plexus injury to the newborn is the most common complication of shoulder dystocia. Most of these injuries resolve before discharge from the hospital. However, some last longer and take weeks or up to 18 months to resolve and a few can be permanent, with varying levels of limited motion depending on the nature and extent of the injury. This injury is caused by deviation 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 and ensuring the head is not rotated. Traction should be directed in line with the axis of the fetal spine. Axial traction poses virtually no risk to the brachial plexus, whereas lateral traction (downward or upward) does. ^{[3, 77]}

As less-experienced obstetricians are more likely to encounter shoulder dystocia-related brachial plexus injury, ^[11]  simulation training can provide experience in management. Residencies with effective training programs have demonstrated decreased brachial plexus injury incidence by a factor of six, and increase in clear and consistent documentation by a factor of seven. Effective training results in improved clinical outcome with fewer adverse outcomes. ^{[70, 72, 75, 73]}

Infants of women who experience a shoulder dystocia complication following a second stage length of 1-3 hours are five times more likely to have a brachial plexus injury than those whose shoulder dystocia complication followed a second stage of less than 1 hour. ^[78] Among infants with permanent shoulder dystocia–associated brachial plexus injuries, an antecedent precipitous second stage is three times more common than a prolonged second stage. ^[12] Given these associations, consideration of preexistent risk factors for shoulder dystocia prior to use of operative vaginal delivery for treatment of a prolonged second stage is prudent. In those circumstances in which a second-stage length is not modifiable by the provider (ie, precipitous second stage), deliberate and conscious awaiting of the next contraction prior to the application of traction has been associated with a lower incidence of shoulder dystocia. ^{[44, 43]}

Although rare, devastating complications of catastrophic shoulder dystocia include neonatal hypoxic ischemic encephalopathy (HIE) and death. ^{[1, 25]} However, the risk of HIE in an otherwise healthy fetus for a head to body time of < 5 minutes is nil. ^[22] The mechanism for oxygen deprivation is usually attributed to variable compression of the umbilical cord during the obstructed delivery. To help prevent this complication, the cord should never be clamped until at least the anterior shoulder has been successfully delivered.

Sudden fetal circulatory collapse can result from a precipitous drop in neonatal blood pressure following delivery after shoulder dystocia. This can occur with the sudden release of the partial (venous greater than arterial) compression of the umbilical cord immediately upon delivery. If unrecognized, improper resuscitation may lead to asphyxia or death. Pediatricians should consider volume resuscitation when a fetus is suddenly more depressed or born with no heart rate immediately following shoulder dystocia. ^[79]

Clinician injury has also been reported. One provider ruptured tendons between the third and fourth fingers from a pincer grasp of the head with those two fingers. ^[80] Another sustained a mallet finger deformity in delivering the posterior arm. ^[81]