Shoulder Dystocia

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Diagnosis and reasoning

This delivery has progressed into obstructed labor - an obstetric emergency which may result in both fetal and maternal death if not treated emergently. When considering the causes of obstructed labor, the adage is that three factors should be considered: the power, the passenger, and the passage. The history of an uncomplicated vaginal delivery earlier along with the adequacy of the pelvis suggests that the 'passage' is normal. Likewise, presence of regular and strong contracts indicates a normal level of 'power'. This most likely means that there is a problem with the 'passenger' (i.e. the fetus) - but there is no evidence of fetal anomalies. However, the fetal birth weight is rather high - meaning that the baby might be too large to deliver. In such an eventuality, one would expect the shoulders (which are the widest part of the fetus) to become impacted. And indeed, this perfectly fits in with the clinical presentation. Note that the fetal head delivered easily, but retracted soon afterwards. This is known as the 'turtle sign' (as it is analogous to a turtle withdrawing it's head into it's shell) - and is pathognomonic of shoulder dystocia. Time is of essence in shoulder dystocia - management should not be delayed pending ultrasonography or other time consuming investigations. The treatment of choice is to place the mother's legs in McRobert's position (i.e. hyperflexed at the hip, with the thigh abducted and externally rotated). This will flatten the lumbar spine and facilitate delivery in over 90% of cases. Suprapubic pressure can also be applied over the posterior aspect of the anterior shoulder; this will further improve the likelihood of delivery. An emergency Cesarean Section should only be performed if the other maneuvers fail; symphysiotomy too is a solution of last resort. Note that cross matching and reservation of blood is very important in these patients, as they are at increased risk of postpartum hemorrhage. An important question we need to answer is: could this situation have been anticipated in advance ? While she did possess several risk factors for shoulder dystocia (i.e. obesity, a large baby, and prolonged gestation), none of these are a contraindication to vaginal delivery; the vast majority of such mothers go on to have an uncomplicated birth. In addition, the fact that she had delivered a very similar baby successfully in the past was strongly suggestive that a successful vaginal delivery might be possible. In retrospect, the prolonged second stage of labour and instrumental delivery were further risk factors for dystocia - but there was no way to predict this in advance. At the end of the day, shoulder dystocia is a highly unpredictable emergency; in most cases, all clinicians can do is to be vigilant. In the patient described in this vignette, the attending obstetrician performed the McRoberts maneuver and suprapubic pressure, freeing the shoulders and allowing a successful delivery.


Discussion

Shoulder dystocia is an acute obstetric emergency which requires additional obstetric maneuvers to deliver the shoulders after normal gentle downward traction has failed. The underlying cause is impaction of the anterior (or less often, posterior) fetal shoulder on the maternal symphysis or sacral promontory, resulting in obstruction of labor. The incidence of shoulder dystocia is unclear; unselected population studies in North America and the United Kingdom have estimated the condition to occur in 0.6% of all deliveries. The risk factors for shoulder dystocia can be broadly classified into prelabor factors and intrapartum factors. Prelabor factors include a history of shoulder dystocia in a previous pregnancy; macrosomia; diabetes mellitus; a maternal BMI > 30 kg/m2; and induction of labor. Intrapartum factors include a prolonged first stage or second stage of labour; secondary arrest of labor; oxytocin augmentation; and instrumental delivery. Note that the above risk factors only predict shoulder dystocia in a few patients; the condition can occur in women with no identifiable risk factors, limiting their usefulness. However, if shoulder dystocia is anticipated an experienced obstetrician should be present at the delivery. Note that even if fetal macrosomia is present, elective Cesarean section is not recommended in non-diabetic mothers. In addition, in women with a history of previous shoulder dystocia a choice between vaginal delivery or elective certain section should be offered to the mother. Clinical findings suggesting shoulder dystocia (aside from failure to delivery the shoulders with routine gentle traction) include difficulty in delivery of the face and chin; the head being tightly applied to the vulva - or retracting (turtle sign), failure of restitution, and failure of the shoulders to descend. Once shoulder dystocia has been diagnosed, systematic and timely management is of the essence. The first step should be to call for help - particularly additional midwives, an obstetrician, a neonatologist and anesthetists. Placement of the mother in McRoberts' position should be the first maneuver performed; gentle traction should be applied on the baby afterwards. In most cases this alone will result in a successful delivery with minimal complications. If the above measure alone proves to be inadequate, suprapubic pressure should be applied (or can be applied simultaneously to improve the outcome). Applying pressure to the posterior aspect of the anterior shoulder reduces the biacromial diameter and helps push the shoulder under the symphysis pubis. Suprapubic pressure should be applied for approximately 30 seconds; if unsuccessful, a rocking movement is recommended. Fundal pressure should not be applied as this is associated with a higher neonatal complication rate. If the above simple measures fail, several more advanced (internal) maneuvers should be used; these include the Rubin II maneuver, Woods corkscrew, reverse Woods screw, release of the posterior arm by flexing the shoulder, and Gaskin maneuver (rolling over onto 'all fours'). Ideally, these should be applied by an experienced clinician - the order of performance may be left to the provider's clinical discretion. Note that the mnemonic "HLEPERR" can aid in remembering the sequence of steps above (H -call for help, E-episiotomy, L-legs in McRoberts' position, P-supra pubic pressure, E-enter pelvis for internal maneuvers, R-release of posterior arm, R-roll over to 'all fours'). Maneuvers of last resort include deliberate clavicular fracture (cleidotomy), the Zavanelli maneuver (cephalic replacement followed by Cesarean delivery), and symphysiotomy. These are rarely required and associated with markedly higher morbidity and mortality. A few other points should be kept in mind - an episiotomy is often performed as it may help with internal maneuvers. However, some studies state that episiotomy is not necessary in all cases - and should be performed as and when needed. In addition, shoulder dystocia is an important medico-legal situation; proper time keeping is essential, and the timeline and sequence of events should be carefully documented. Shoulder dystocia is associated with significant fetal and maternal complications. Important fetal complications include brachial plexus injury, clavicular fracture, humeral fracture, fetal hypoxia with or without permanent neurological deficits, and fetal death. Of these, brachial plexus injuries are the most common (and have an incidence which is apparently independent of operator experience). However, permanent neurological damage is rare. Important maternal complications include postpartum hemorrhage (occurring in 11% of cases), third or fourth degree perineal tears, uterine rupture, and rectovaginal fistula formation.


Take home messages

  1. Shoulder dystocia is a highly unpredictable emergency which can occur in the absence of overt risk factors.
  2. In the majority of patients, placement in McRoberts' position allows delivery of the shoulders with minimal complications.
  3. Brachial plexus injuries are the most common complication, although permanent neurological impairment is rare.
  4. Shoulder dystocia is an important medico-legal situation - accurate and detailed record keeping is essential.

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