Shoulder dystocia is an obstetric emergency caused by impaction of one or both fetal shoulders against the mother’s symphysis pubis after the head has been delivered, that is not relieved by gentle traction, and requires additional obstetric manoeuvres for delivery. The incidence is variable and is quoted to be 0.6-1.4% of all vaginal deliveries. In 50% of cases it is unanticipated, and although there is a recognised association with fetal macro- somia, it may occur in fetuses with a normal birth weight. Maternal risk factors include a previous history of shoulder dystocia, diabetes (gestational and pre-existing), post-dates pregnancy and cephalopelvic disproportion. It is also associated with a prolonged second stage and assisted deliveries.
It is important for obstetric anaesthetists to understand shoulder dystocia and its management, since they may be required to provide immediate assistance, and prompt intervention may be life-saving.
Problems and special considerations
Fetal brachial plexus injury, most commonly Erb’s palsy, occurs in 4-16% of cases. Most recover, usually within 6-12 months, but up to 10% of affected babies suffer some permanent damage. Humeral and clavicular fractures have also been reported.
Fetal hypoxia may occur, and if prolonged this can lead to severe fetal morbidity or even death.
Maternal soft tissue damage with extensive third- or fourth-degree tears have been reported. Uterine atony leading to massive obstetric haemorrhage, and uterine rupture, may occur.
Management options
A previous history of shoulder dystocia does not mandate induction of labour or delivery by caesarean section in subsequent pregnancies. However, measures should be taken to anticipate this obstetric emergency if the mother has any associated risk factors.
The classic sign of shoulder dystocia is described as the ‘turtle sign’, in which the head appears on the perineum with contractions and then retracts between contractions. Another is fetal facial swelling caused by venous obstruction. Manoeuvres to dislodge the impacted shoulder are described in shoulder dystocia guidelines and include the McRoberts manoeuvre, in which the mother’s legs are flexed and abducted to enable cephalad rotation of the pelvis and augmentation of uterine contractions. Suprapubic pressure applied downwards and laterally with the McRoberts manoeuvre may enable the passage of the anterior shoulder under the symphysis pubis. Other manoeuvres include internal rotation, and placing the mother on all fours to facilitate descent of the posterior shoulder.
Rarely, extreme measures such as deliberate fracture of the fetal clavicle, maternal symphysiotomy or the Zavenelli manoeuvre (attempting to push the fetal head back in the vagina and delivering the baby by caesarean section) have been attempted, though their place has been questioned. Symphysiotomy is classically done under local anaesthesia but the Zavenelli manoeuvre (a high-risk procedure for both mother and fetus) requires general anaesthesia - which must be administered in the most difficult and fraught circumstances and therefore should not be undertaken lightly.
Key points
• Shoulder dystocia is an obstetric emergency associated with significant fetal and maternal complications.
• Anticipation and preparation are paramount in cases where risk factors exist.
• The anaesthetist may be called upon to administer general anaesthesia in a situation that is stressful for all concerned.
Further reading
Dahlke JD, Bhalwal A, Chauhan SP. Obstetric emergencies: shoulder dystocia and postpartum haemorrhage. Obstet Gynecol Clin North Am 2017; 44: 231-43.
Hansen A, Chauhan SP. Shoulder dystocia: definitions and incidence. Semin Perinatol 2014; 38:184-8. Lim MN, Gale A, Debroy B. Early resort to general anaesthesia in severe shoulder dystocia. J Obstet Gynaecol 2008; 28: 436-7.
Royal College of Obstetricians and Gynaecologists. Shoulder Dystocia. Green-top Guideline 42.
London: RCOG, 2012 (updated February 2017). www.rcog.org.uk/en/guidelines-research-services/ guidelines/gtg42 (accessed December 2018).