Dystocia describes difficulty during labour.

Epidemiology

Dystocia occurs in 1% of vaginal deliveries.¹

Aetiology

These are easily remembered as 'The Powers' (uterus), 'The Passenger' (fetus) and 'The Parts' (pelvis).

• Uterine factors:
  Good contractions start at the fundus and move down towards the pelvis. If uterine activity is unco-ordinated or contractions short or infrequent then labour will be difficult and prolonged. Primigravid mothers may be more at risk of dystocia as they have a degree of uterine unco-ordination which is why their labours tend to be longer. Oxytocin can enhance and co-ordinate uterine contractions.
• Fetal factors:
  Position or lie - e.g. transverse or breech, macrosomia, shoulder dystocia (this results as a combination of fetal factors and pelvic passage factors).
• Pelvic passage factors:
  A pelvis with a round brim is very favourable in labour; however, some women have a long and oval brim. A small pelvic brim should be suspected if the fetal head has not engaged into the pelvis by 37 weeks' gestation. Other factors that can lead to cephalopelvic disproportion are scoliosis, kyphosis and, historically, rickets. Shoulder dystocia in part results from a small or abnormal pelvic inlet.

Risk factors for dystocia

• Diabetes mellitus.
• Fetal macrosomia.
• Maternal obesity.
• Induction of labour.
• Prolonged labour.
• Oxytocin - too much can lead to hyperstimulation of the uterus.²

It is important to note that diabetes mellitus and macrosomia are associated. It is routine for mothers with diabetes to have an ultrasound scan near term to estimate fetal weight and thus anticipate difficulties.

Two specific types of dystocia

Shoulder dystocia

During the peripartum period the infant's head usually lies to the left and then rotates to the occipito-anterior position and the head is delivered first. Following this, the shoulders lie in the anteroposterior position and then pass the pelvic brim. However, if the shoulders become stuck at this position, the infant can inhale, as the mouth and nose are out of vagina, but the chest cannot expand as it is stuck in the pelvic brim.³ This will rapidly lead to hypoxia and death of the fetus if not delivered quickly.⁴

The incidence in the UK is thought to be 0.6%.¹

Management of shoulder dystocia is discussed under 'For shoulder dystocia', below.

Cervical dystocia

This is where the cervix fails to dilate during labour.

Failure of cervical dilatation can be due to previous cone biopsy or cauterisation for cervical dysplasia. Other reasons for failure to dilate include trauma. Sometimes if there are unco-ordinated uterine contractions then the failure of cervical dilation may be secondary to this and this should respond to oxytocin. If dystocia continues despite this then the infant will need to be delivered by Caesarean section.

Management of all cases of dystocia

• All cases of dystocia are an obstetric emergency.
• This group of mothers need to be in a labour unit and obstetricians should be present.
• The anaesthetist and paediatrician should be informed.
• Oxytocin can be used if abnormal uterine contractions are the cause of dystocia.
• Episiotomy may help but is not necessary.
• Assisted delivery may be required, e.g. forceps or ventouse and, if this fails, the mother may need an urgent Caesarean section.

However, elective Caesarean section or routine assisted deliveries are not recommended for high-risk mothers.

For shoulder dystocia

Also see the Royal College of Obstetricians and Gynaecologists (RCOG) guidelines for shoulder dystocia.¹

• Stop the mother pushing - get help.
• McRoberts' manoeuvre - the patient hyperflexes her hips so they are against her abdomen. Mothers in labour may not have enough energy to do this by themselves and may need the assistance of others in the room - which is usually the case. Posterolateral pressure is applied suprapubically with traction on the fetal head. This is the most effective procedure and should be performed first (success rates are up to 90%).¹
• If this fails, an episiotomy may be needed - but the need for a Caesarean should be considered.⁵
• Rubin's manoeuvre - press on the posterior fetal shoulder, thereby creating more space to allow the anterior shoulder to be delivered.
• Wood's screw manoeuvre - turning the anterior shoulder to the posterior position.
• If these fail then delivery of the posterior shoulder may help.⁵
• However, at all times the need of a Caesarean section should be considered and should not be delayed.

Complications

• Perinatal morbidity and mortality - from hypoxia and acidosis.
• Brachial plexus injury.⁶
• Postpartum haemorrhage.
• Perineal tears.

Document references

1. Shoulder dystocia, Royal College of Obstetricians and Gynaecologists (2005)
2. Stubbs TM; Oxytocin for labor induction.; Clin Obstet Gynecol. 2000 Sep;43(3):489-94. [abstract]
3. Chamberlain G, Steer P; ABC of labour care: unusual presentations and positions and multiple pregnancy. BMJ. 1999 May 1;318(7192):1192-4.
4. Neilson JP, Lavender T, Quenby S, et al; Obstructed labour.; Br Med Bull. 2003;67:191-204. [abstract]
5. Morrison EH; Common peripartum emergencies.; Am Fam Physician. 1998 Nov 1;58(7):1593-604. [abstract]
6. Doumouchtsis SK, Arulkumaran S; Are all brachial plexus injuries caused by shoulder dystocia? Obstet Gynecol Surv. 2009 Sep;64(9):615-23. [abstract]

Internet and further reading

• Breeze AC, Lees CC; Managing shoulder dystocia. Lancet. 2004 Dec 18-31;364(9452):2160-1.

Acknowledgements