Chapter 66 Shoulder dystocia

After reading this chapter, you will be able to:

• identify risk factors for shoulder dystocia

• describe shoulder dystocia and be able to recognize the signs which suggest it

• demonstrate a series of manoeuvres that are likely to be effective in resolving shoulder dystocia

• identify which manoeuvres are not likely to be effective in this emergency situation

• state which manoeuvres are likely to cause harm if undertaken

• anticipate the consequences of shoulder dystocia for the mother and the infant

• perform or participate in a locally agreed drill or procedure for shoulder dystocia

• provide support and information to women and their families during and after a case of shoulder dystocia.

Introduction

Shoulder dystocia is an obstetric emergency with a potentially catastrophic outcome. It refers to deliveries where manoeuvres other than gentle downward traction are needed to complete the delivery of the anterior shoulder (Resnik 1980).

Mechanism

In a normal labour the shoulders enter the pelvic brim in the oblique or transverse diameter. (For a complete description of the normal mechanism of labour, see Ch. 37.) In shoulder dystocia there is an arrest of the normal mechanism of labour as the shoulders attempt to enter the pelvis in the anteroposterior diameter of the pelvic brim. The diameter of the fetal shoulders or bisacromial diameter is 12.4 cm and should fit comfortably through the widest diameter of the pelvic brim. Shoulders are sufficiently flexible to allow those of even a large baby to negotiate the pelvis.

There is no current agreement on a definition for shoulder dystocia. Smeltzer (1986) suggests that shoulder dystocia is a failure of the shoulders to spontaneously traverse the pelvis after the fetal head has been delivered.

Some or all of the following will alert midwives to suspect that shoulder dystocia has occurred:

• difficulty with delivery of the face and chin

• head remaining tightly applied to the vulva or even retracting (turtle sign)

• failure of restitution of the head

• failure of the shoulders to descend (RCOG 2005).

The turtle sign is caused by reverse traction from the shoulders. The anterior shoulder is wedged onto the symphysis pubis and the posterior shoulder may still be above the pelvic brim (Fig. 66.1). Pulling to deliver the anterior shoulder is likely to impede delivery by wedging the infant’s anterior shoulder more firmly onto the symphysis pubis and can cause damage to the brachial plexus (see Fig. 66.10).

Figure 66.1 Shoulder dystocia.

The midwife must recognize shoulder dystocia and summon help immediately from midwifery, obstetric, paediatric and anaesthetist colleagues, as the outcome for both mother and infant is potentially very serious.

The midwife’s anxiety is likely to be communicated to the mother even if little is said. The midwife should remain calm and in control of the situation, and maintain communication with the mother and her partner.

Incidence and risk

The incidence of shoulder dystocia is around 0.6% at term, but the risk increases to 1.3% by 42 weeks’ gestation (Johnstone & Meyerscough 1998, RCOG 2005). However, a lack of agreement over the definition affects the number of cases reported (Johnstone & Myerscough 1998).

The risk of shoulder dystocia rises with increasing birthweight and length of gestation, birth order and maternal age (Acker et al 1986, Gross et al 1987, Johnstone & Myerscough 1998). Johnstone & Myerscough (1998) point out that half of all babies with shoulder dystocia weigh less than 4 kg and are not considered to be large, and only 4% of large babies suffer shoulder dystocia.

Mortimore & McNabb (1998) suggested that some practitioners may use the term shoulder dystocia to describe any general difficulty with the delivery of the shoulders. If RCOG (2005) diagnostic criteria for shoulder dystocia cannot be fulfilled, then ‘difficulty with delivery of the shoulders’ should be recorded to avoid overdiagnosis (Mahran et al 2008).

Identification of risk factors

Ideally, all potential cases of shoulder dystocia would be identified antenatally; the associated maternal and neonatal morbidity and mortality could then be prevented. The sensitivity of single predictive risk factors is poor. At present, midwives and obstetricians can do no more than anticipate the problem by identifying those factors which give a strong index of suspicion.

Maternal obesity is a frequently occurring factor associated with shoulder dystocia (maternal BMI >30 at booking, or weight at delivery >90 kg) (RCOG 2005). The greater the maternal weight, the higher the risk (Athukorala et al 2007).

Maternal diabetes and gestational diabetes are associated with asymmetrical fetal growth. The body and particularly the shoulders are larger than in babies of mothers who are not diabetic (Acker et al 1985).

Spellacy et al (1985) studied the data from 33,545 deliveries and concluded that women with either insulin-dependent or gestational diabetes are more likely to deliver a macrosomic infant and are therefore at a higher risk of a delivery complicated by shoulder dystocia.

Fetal macrosomia is the strongest independent risk factor for shoulder dystocia (Athukorala et al 2007). Infants of non-diabetic mothers who have birthweights of 4000–4449 g have a 10% risk of shoulder dystocia, while infants of the same weight born to diabetic mothers have a 31% risk of developing shoulder dystocia, because of their asymmetrical growth (Acker et al 1985, Spellacy et al 1985).

A previous delivery complicated by shoulder dystocia is a predictive risk factor, with a recurrence rate of around 10% for subsequent deliveries (Olugbile & Mascarenhas 2000, Smith et al 1994).

Use of ultrasound to predict the macrosomic fetus

Ultrasonic estimation of fetal weight is widely used, as it is objective and can be reproduced (Combs et al 1993). However, Chauhan et al (1992) suggest that ultrasonic diagnosis of the large infant is generally no more accurate than clinical estimation and that if a woman has had a baby before, her own estimate is likely to be as good as an ultrasound measurement. Elective induction for infants diagnosed as macrosomic on ultrasound scan increases the risk of caesarean section and does not prevent shoulder dystocia (Hall 1996, RCOG 2005).

In spite of the inadequacy of ultrasound estimation of fetal weight, it is currently used along with clinical judgement to assess the safest method of delivery, especially for the postmature, large for gestational age or suspected macrosomic fetus.

Prediction of impending shoulder dystocia

Most labours preceding shoulder dystocia are normal (McFarland et al 1995). In some cases the first hint of trouble the midwife may experience during a delivery is the slow extension of the baby’s head and then the chin remaining tight against the mother’s perineum (Coates 1995). In spite of current technology, shoulder dystocia usually occurs unexpectedly (RCOG 2005).

Unfortunately, the absence of risk factors cannot be relied upon to exclude the possibility of shoulder dystocia. It is therefore important that the midwife has a sound knowledge of the interaction between the physiology and mechanism of labour and the manoeuvres that may be used to complete the delivery in the shortest time possible. This is to ensure the best outcome for the mother and her infant. All members of the labour ward team should be familiar with the agreed protocol, and ‘drills’ should be practised on a regular basis by all grades of staff (Draycott et al 2008, MCHRC 1998).

Manoeuvres for management of shoulder dystocia

The following descriptions of manoeuvres are arranged from the simple, requiring only movement of the mother, to the complex, where direct manipulation of the baby is required. These manoeuvres cannot really be learned or fully understood by reading alone and it is suggested that the reader works through the manoeuvres using a doll and pelvis or phantom.

McRoberts’ manoeuvre

This is the first choice of manoeuvre in most circumstances as it has been proven to be safe and effective. The manoeuvre (Fig. 66.2) requires the mother to lie flat on her back (or with a slight lateral tilt to prevent supine hypotension), then she is assisted into an exaggerated knee–chest position (Gonik et al 1983).

Figure 66.2 McRoberts’ manoeuvre.

Once the mother has adopted this position, the midwife should be able to proceed with a normal delivery of the shoulders. Smeltzer (1986) suggests that this manoeuvre:

1 rotates the symphysis pubis superiorly by approximately 8 cm

2 elevates the anterior shoulder

3 pushes the posterior shoulder over the sacrum

4 flexes the fetal spine

5 straightens maternal lordosis

6 opens the pelvic inlet to its maximum

7 brings the inlet perpendicular to the maximum expulsive force

8 removes weight-bearing forces from the sacrum, and

9 removes the sacral promontory as a point of obstruction (Figs 66.3 and 66.4).

Figure 66.3 Diagram to show brim of pelvis in dorsal position.

Figure 66.4 Diagram to show brim of pelvis in McRoberts’ position.

This was supported by later radiological studies (Gherman et al 2000).

Maternal and fetal models were used by Gonik et al (1989) to assess the forces used to extract the fetal shoulders. The McRoberts’ manoeuvre was compared with the lithotomy position and consistently required less force to remove the shoulders.

RCOG (2005) advocates the use of the McRoberts’ manoeuvre as a first step if shoulder dystocia is diagnosed, and, if the manoeuvre is unsuccessful at the first attempt, to try it a second time before attempting other manoeuvres.