The term 'dystocia' means difficult labour (childbirth). During labour, there are numerous factors that could be responsible for dystocia including in-coordinate uterine activity, abnormal foetal lie or presentation or absolute or relative cephalopelvic disproportion.

Foetal lie is defined as the relationship between the long axis of the foetus and the long axis of the maternal spine; a longitudinal lie is the normal. Dystocia is associated with abnormal foetal lie such as a transverse lie. Cephalopelvic disproportion is said to occur when there is a large foetal head in the presence of a much smaller maternal pelvis.

There are two specific types of dystocia - cervical dystocia and shoulder dystocia. Cervical dystocia is defined as difficulty in labour resulting from failure of the cervix to dilate. In the remaining part of this article, we'll focus on shoulder dystocia - associated risk factors as well as complications.

According to the Royal College of Obstetricians and Gynecologists, the incidence of dystocia in the United Kingdom is around 0.5% or 1 in 200.

What is shoulder dystocia?

    Shoulder dystocia is a specific case of dystocia where there is a difficulty with delivery of the foetal shoulders. In passing through the pelvis, the foetal head and shoulders rotate to make use of the widest diameters of the maternal pelvis. After delivery of the head, restitution occurs and the shoulders rotate into the antero-posterior (AP) diameter of the pelvic outlet. However, if the shoulders have not entered the pelvic inlet, the anterior shoulder may become caught above the maternal pubic symphysis. Occasionally, both shoulders may remain above the pelvic brim. Shoulder dystocia is therefore, diagnosed during labour when the shoulder fails to be delivered shortly after the foetal head.

Risk factors associated with shoulder dystocia

    The following are some of the risk factors that have been associated with the development of shoulder dystocia during labour:

        • Large foetus - Even in the presence of a well sized maternal pelvis, shoulder dystocia can occur during delivery if the foetus is macrosomic. A macrosomic foetus is defined as one with a weight greater than 4.0kg.
        • Small maternal pelvis - Shoulder dystocia can occur if the dimensions of a woman's pelvis are smaller than those accepted as normal. Under these circumstances, delivering a normal foetus becomes difficult.
        • Maternal obesity (BMI greater than 35) - Maternal obesity is a known cause of foetal macrosomia or a large foetus described earlier.
        • Diabetes mellitus - Maternal diabetes mellitus is a leading cause of foetal macrosomia.
        • Post maturity.
        • Previous shoulder dystocia.
        • Prolongation of late first stage of labour.
        • Prolonged second stage of labour.
        • Assisted vaginal delivery.

Complications of shoulder dystocia

    Shoulder dystocia is a foetal emergency because if poorly managed, it could lead to foetal death. Complications that could result from shoulder dystocia include:

      • Foetal Complications

            • Brachial plexus injuries - in an effort to deliver the baby, inappropriate traction may be applied, causing stretching of the brachial plexus causing nerve damage. The most common form of brachial plexus injury associated with shoulder dystocia is Erb's palsy. Klumpke's palsy could also occur. Fortunately, most brachial plexus birth injuries are transient. Most of such injuries resolve between 2 weeks and 12 months but up to 15% of injuries result in permanent damage.
            • Fractures - including fractures of the clavicle and the humerus (long bone of the arm).
            • Birth asphyxia.
            • Cerebral damage - vessels of the foetal neck become occluded upon delivery of the head. Prolonged occlusion of these vessels for a few minutes is likely to cause varying degrees of cerebral damage.
            • Foetal death - the occlusion of the vessels may be prolonged long enough to cause foetal death.
      • Maternal Complications

            • Postpartum hemorrhage.
            • Rectovaginal fistula.
            • Symphyseal separation or diathesis, with or without transient femoral neuropathy.
            • Third or fourth degree episiotomy or tear.
            • Uterine rupture.

Figure: A representation of shoulder dystocia.

shoulder dystocia


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