On successfully completing this topic, you will be able to:
understand the aetiology and complications of shoulder dystocia
understand the risk factors for shoulder dystocia
be aware of strategies that can be tried to prevent shoulder dystocia
be confident in understanding the variety of obstetric manoeuvres used to overcome shoulder dystocia
appreciate the benefits of formal skills/drills training on maternal and fetal outcomes in cases of shoulder dystocia.
Introduction
Shoulder dystocia remains one of the most dreaded obstetric complications and one that is often unanticipated. It is associated with significant perinatal mortality and morbidity, maternal morbidity and is a costly source of litigation. In this chapter, a number of matters will be addressed.
Definition and incidence
Shoulder dystocia describes difficulties encountered with delivering the shoulders after the fetal head is born. Discrepancies in the definition have resulted in differences in the reported incidence of this obstetric emergency from 0.15% to 2% of all vaginal deliveries. MOET considers shoulder dystocia to be a condition requiring special manoeuvres to deliver the shoulders that have been arrested due to impaction of the anterior shoulder above the symphysis pubis.
Clinical risks and outcomes
Fetal mortality and morbidity
Shoulder dystocia is still a significant cause of term fetal mortality. In the CESDI annual report for 1993,1 shoulder dystocia was responsible for 8% of all intrapartum fetal deaths.A later, focused report (1998) critically reviewed 56 cases of death associated with shoulder dystocia: 47% had died despite delivery within 5 minutes and, in 37 (66%) cases, the level of substandard care offered by professionals was graded at ‘level 3’ (i.e. a different management would have likely resulted in an improved outcome). The babies were delivered by both midwives and medical staff, emphasising the need for all professionals involved in delivery to be aware of appropriate drills.
Fetal morbidity:
cerebral hypoxia
cerebral palsy
fracture clavicle and/or humerus
brachial plexus injuries.
Following delivery of the head, the umbilical cord pH falls by 0.04 unit/minute, in addition, cranial venous congestion occurs, which exacerbates the fetal insult. As a result, delay in completing the delivery may result in asphyxia and, if the interval between head and trunk delivery is prolonged, permanent neurological deficit may occur. Delivery should occur within 5 minutes and permanent injury is progressively more likely with delays above 10 minutes.
Brachial plexus injuries can occur in shoulder dystocia due to downward traction with excessive lateral flexion of the neck, which stretches its soft tissues. Erb’s palsy is the most common of these. A study in 2000 found 62 cases of brachial plexus injury in 13 366 deliveries (incidence 0.46%): 22 recovered completely within a month, while a further 23 had delayed but complete recovery.2 Of 17 with residual paresis, 11 underwent surgery but only three had severe paresis. The most significant marker to predict the likelihood of ‘nonrecovery’ was birthweight greater than 4000 g (OR 51).
It has been suggested that intrauterine maladaptation may play a role in brachial plexus impairment, implying that brachial plexus impairment should not be taken as prima facie evidence of birth-process injury. The mechanism of damage may not always be clear, as brachial plexus injury has also been reported in the opposite arm to the trapped shoulder and also without any recorded dystocia. Furthermore, it has also been reported after delivery by CS, although clearly injudicious traction on the fetal head and neck can also occur during this delivery.
Bony injuries in the form of fractured clavicle or humerus can also occur. These fractures usually heal quickly and have a good prognosis.
Antenatal risk factors
Antenatal risk factors are so common that they lack sensitivity and specificity, and the majority of cases of shoulder dystocia occur without any risk factors. There is a strong correlation between fetal weight and shoulder dystocia. Increasing obesity, diabetes and gestational diabetes all increase the likelihood of macrosomia; however, shoulder dystocia occurs with a normal fetal weight therefore all professionals need to be prepared for unexpected shoulder dystocia at all deliveries.
Intrapartum risk factors
Secondary arrest and slow progress in the first stage of labour can be associated with increased incidence of shoulder dystocia, but many studies have shown labour abnormalities to be similar in both the shoulder dystocia and the control groups, making clinical predictors for subsequent development of shoulder dystocia imprecise.
Shoulder dystocia is more frequently encountered in assisted vaginal deliveries. Boekhuizen et al. analysed 256 vacuum extractions and 300 forceps deliveries.3 They found an incidence of 4.6% of shoulder dystocia compared with 0.17% of all cephalic vaginal deliveries. This emphasises the importance of particularly careful abdominal and vaginal assessment before performing assisted deliveries for clinically macrosomic babies.
How does shoulder dystocia happen?
The posterior shoulder usually enters the pelvic cavity, while the anterior shoulder remains hooked above the symphysis pubis. In the more severe forms of shoulder dystocia, both shoulders do not cross the pelvic brim.
Strategies suggested for prevention and management of shoulder dystocia
Identifying risk factors
Identify the risk of shoulder dystocia antenatally and recommend clearly in the mother’s notes that an experienced obstetrician should be available for the second stage.
Training and teaching
In the CESDI report 1993 it is stated that: ‘There should be regular rehearsals of emergency procedures and training sessions in the management of rare or troublesome complications for obstetricians and midwives involved in care.’ Such complications include obstructed delivery… and shoulder dystocia.
There is now clear evidence of benefit from the work of the research team led by Draycott and Crofts. In a randomised trial of 450 clinicians, formal skills/drills training in SD resulted in an increase in successful delivery rate (72% prior to training versus 94% post-training), with a reduction in total force applied.4 Of even greater importance is the improvement in neonatal outcomes following the introduction of training.5 In an analysis of >29 000 births, the use of correct manoeuvres was significantly increased. This resulted in a significant reduction in neonatal injury at birth after shoulder dystocia: 30/324 (9.3%) to 6/262 (2.3%) (relative risk [RR] 0.25 [CI 0.11–0.57]).
Clinical approach
Prevention
Prevention by performing CS for macrosomic infants is not recommended from the evidence available.
Estimates of fetal weight antenatally are notoriously unreliable (especially at the extremes). Many cases of shoulder dystocia occur in babies of average weight, and most macrosomic fetuses delivered vaginally do not suffer from shoulder dystocia. Most cases of shoulder dystocia can be overcome without trauma to mother or baby if proper precautions are taken. Abdominal delivery is not 100% safe to the baby and causes morbidity to the mother. Thus, a policy of elective CS for all clinically big babies will not be effective in reducing the incidence of shoulder dystocia and subsequent brachial plexus injuries.
Prevention by induction of labour for suspected macrosomia
Induction of labour has been considered as an option for managing mothers with suspected macrosomic babies to try to reduce the incidence of shoulder dystocia and subsequent birth trauma. A 1995 study reviewed 186 mothers with suspected macrosomic fetuses at term.6 Labour was induced in 46 cases, 23.9% of them needed CS while, with spontaneous onset of labour in 140 cases, the CS rate was 14%. This difference was statistically significant, regardless of parity or gestational age. The frequencies of shoulder dystocia, 1 minute Apgar score less than 7 and abnormal umbilical blood gas were not different. They concluded that spontaneous labour is associated with a lower chance of CS than induced labour when the birthweight is 4000g and above.
The situation in women with diabetes is different, for reasons mentioned earlier. Various authorities recommended CS for babies with estimated fetal weight 4000g or above. Induction of labour is also recommended for women with diabetes at 38 weeks, especially if their diabetic control has not been ideal, not only to avoid intrauterine death but also shoulder dystocia and birth trauma.
Documentation
Risk factors should be documented in the notes, especially if they are multiple. It is also recommended that an experienced clinician is present during the second stage. It is strongly recommended that events, manoeuvres and accurate times are documented in the notes. Using a proforma for this ensures all important facts are noted.
Early detection
Have a plan of action
As shoulder dystocia is infrequently predictable, every clinician should be armed with a plan of action; that is, a sequence of manoeuvres. All manoeuvres result from one (or a combination of) the following three mechanisms:
increase in the available pelvic diameter
narrowing of the transverse (bisacromial) diameter of the shoulders by adduction
movement of the bisacromial diameter into a more favourable angle relative to the pelvic inlet (oblique diameter is larger than the anteroposterior pelvic diameter).
Plan of action
1 Call for help.
2 Draw buttocks to edge of bed.
3 Consider episiotomy.
4 McRoberts’ manoeuvre + moderate traction.
5 Suprapubic pressure + moderate traction.
6 Episiotomy (if not already cut) to allow space to insert hand for internal manoeuvres.
7 Deliver posterior arm and shoulder or internal rotational manoeuvres (including Woods’ screw manoeuvre).
8 Repeat manoeuvres or try:
(a) Digital axillary traction
(b) PAST (posterior axillary sling).
9 Change of position (‘All fours’ or ‘Gaskin’ manoeuvre).
11 Ensure comprehensive and contemporaneous written records.
Call for help
This includes calling the most experienced obstetrician available, a paediatrician and an anaesthetist, and other nursing and ancillary staff as available.
Episiotomy
Episiotomy is recommended to allow more room for manoeuvres, such as delivering the posterior arm or internal rotation of the shoulders. Although it has been suggested that episiotomy does not affect the outcome of shoulder dystocia, there is strong evidence to suggest that the incidence of vaginal lacerations with shoulder dystocia is high and performing an episiotomy to reduce the chance of having severe lacerations is recommended. The main reason for recommending an episiotomy is to allow the operator more space to use the hollow of the sacrum to perform the different internal manoeuvres.
McRoberts’ manoeuvre (with or without moderate traction)
Both thighs are sharply flexed, abducted and rotated outwards (knees to shoulders). The bed should be flat and legs should not be in lithotomy poles, as this would limit the amount of flexion obtained. This position serves to straighten the sacrum relative to the lumbar vertebrae and causes cephalic rotation of the pelvis to occur, which helps to free the impacted shoulder. One study tested McRoberts’ position with laboratory maternal pelvic and fetal models. Their findings showed that this manoeuvre reduced the amount of traction needed and the likelihood of subsequent brachial plexus injuries or fractured clavicle. For this reason, patients should be put in McRoberts’ before applying appropriate traction on the fetal neck. Lurie et al. reviewed 76 cases of shoulder dystocia and found that McRoberts’ manoeuvre was sufficient to achieve delivery of the impacted shoulder in 67 cases (88%).7 McRoberts’ manoeuvre is associated with the least neonatal trauma.
The traction applied during delivery can be measured objectively using the PROMPT Trainer with studies showing a mean maximum applied traction force of 106Newtons, but a range varying from 6 to >250N. Computer modelling suggests that maximum traction force should not exceed 100N in order to reduce the risk of neonatal brachial plexus injury.
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