Dystocia

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management | References

Definition

Dystocia refers to difficult or obstructed labour, where the fetus does not progress through the birth canal despite strong uterine contractions. One of the most severe forms of dystocia is shoulder dystocia, where the fetal shoulders become lodged behind the maternal pubic symphysis after the head has been delivered.

Aetiology

Dystocia can arise due to a variety of factors, including:

• Fetal Macrosomia: Large fetal size (often over 4,000 grams) increases the risk of shoulder dystocia.
• Maternal Pelvic Abnormalities: A small or abnormally shaped pelvis may impede the passage of the fetus.
• Abnormal Fetal Position: Malpresentation, such as occiput posterior, can lead to obstructed labour.
• Prolonged Second Stage of Labour: Extended duration of pushing can increase the risk of dystocia.
• Maternal Obesity: Increased maternal body mass index (BMI) is associated with a higher incidence of dystocia.

Pathophysiology

Shoulder dystocia occurs when the fetal shoulders become trapped behind the maternal pelvis after the fetal head has been delivered. The anterior shoulder typically becomes impacted behind the pubic symphysis, while the posterior shoulder may be obstructed by the sacral promontory. The condition requires immediate intervention to avoid significant fetal morbidity or mortality due to hypoxia.

Risk Factors

• Fetal macrosomia (birth weight >4,000 grams).
• Maternal obesity.
• Diabetes mellitus (gestational or pre-existing).
• Prolonged second stage of labour.
• Instrumental delivery (e.g., forceps or vacuum).
• Previous shoulder dystocia in a prior pregnancy.

Signs and Symptoms

• Turtle Sign: A key indicator of shoulder dystocia where the fetal head retracts against the perineum after delivery, resembling a turtle pulling its head back into its shell. This is due to the shoulders being stuck.
• Failure of the fetal shoulders to deliver spontaneously after the head has emerged.
• Difficulty in delivering the face and chin over the perineum.

Investigations

Shoulder dystocia is typically diagnosed clinically during delivery, and no specific investigations are required at the time. However, assessing fetal size and position during prenatal visits can help anticipate potential complications:

• Ultrasound: May be used to estimate fetal weight and position.
• Pelvimetry: Occasionally used to assess maternal pelvic dimensions, although not routinely performed.

Management

Shoulder dystocia is an obstetric emergency requiring prompt management to prevent fetal hypoxia and injury:

• Initial Maneuvers:
  • McRoberts Maneuver: A widely used technique where the mother's legs are hyperflexed tightly to her abdomen, which flattens the sacrum and changes the angle of the pelvis, helping to release the fetal shoulder.
  • Suprapubic Pressure: Applied by an assistant to dislodge the anterior shoulder from behind the pubic symphysis. This pressure should be applied from the side, not directly on the uterus.
• Additional Maneuvers:
  • Woods Corkscrew Maneuver: The clinician rotates the fetal shoulders by applying pressure to the posterior shoulder to facilitate delivery. This rotation can help free the impacted shoulder.
  • Rubin Maneuver: Involves applying pressure on the accessible shoulder in the direction of the fetal chest to reduce the shoulder width and assist with delivery.
• Advanced Techniques:
  • Delivery of the Posterior Arm: The posterior arm is grasped and delivered first, reducing the shoulder diameter and facilitating delivery.
  • Zavanelli Maneuver: This involves pushing the fetal head back into the birth canal followed by an emergency caesarean section. This is a last resort due to the risks involved.
  • Symphysiotomy: A surgical procedure to partially divide the pubic symphysis. This is rarely performed and is generally considered a last resort.
• Post-Delivery Care:
  • Neonatal Assessment: Immediate assessment and resuscitation if needed. Check for brachial plexus injury, clavicle fractures, and other birth-related injuries.
  • Maternal Care: Monitor for postpartum haemorrhage and any trauma to the birth canal.

References

1. NHS (2024) Shoulder Dystocia. Available at: https://www.nhs.uk/conditions/shoulder-dystocia/ (Accessed: 24 June 2024).
2. National Institute for Health and Care Excellence (2024) Intrapartum Care: Management of Shoulder Dystocia. Available at: https://www.nice.org.uk/guidance/ng121 (Accessed: 24 June 2024).
3. Royal College of Obstetricians and Gynaecologists (2024) Green-top Guideline No. 42: Shoulder Dystocia. Available at: https://www.rcog.org.uk/en/guidelines-research-services/guidelines/gtg42/ (Accessed: 24 June 2024).
4. British Medical Journal (2024) Shoulder Dystocia: Diagnosis and Management. Available at: https://www.bmj.com/content/350/bmj.h679 (Accessed: 24 June 2024).

Back to Top