Labour Dystocia and Abnormal Labour Patterns
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Direct answer
Labour dystocia is abnormal or slow progress of labour caused by a problem with the power of the contractions, the passage or the passenger. Its main patterns are a prolonged latent phase, protraction of active-phase dilatation, arrest of dilatation and arrest or delay of descent in the second stage. The power, passage and passenger framework sorts the causes and guides augmentation or caesarean section.
What you must remember
- Power: inadequate contractions in frequency, strength or duration cause hypotonic dysfunction, which is a different problem from hypertonic uterine action.
- Passage: a contracted bony pelvis or soft-tissue obstruction, such as fibroids or an abnormal cervix, can impede descent.
- Passenger: fetal size, presentation, position and anomalies, including macrosomia, malposition and hydrocephalus, can slow progress.
- Prolonged latent phase: classic textbook limits are about 20 hours in a nulliparous and 14 hours in a multiparous woman, although current guidance uses different thresholds.
- Protraction: a slow active phase, with dilatation running below the partograph line, is managed differently from a complete arrest.
- Arrest of dilatation: no cervical change for about four hours despite adequate contractions is a common working definition.
- Psyche: maternal anxiety and fear can slow labour, and it is sometimes recorded as the fourth P.
A structured approach to slowed labour
Most dystocia questions reduce to naming the pattern, locating the cause within the three Ps and choosing between augmentation and caesarean section. The table sets out the four main patterns together, since the time limits and first steps are easiest to compare side by side.
| Pattern | Stage | Typical working definition | Usual first step |
|---|---|---|---|
| Prolonged latent phase | First | Beyond about 20 h (nulliparous) or 14 h (multiparous) | Reassess, analgesia, consider augmentation |
| Protraction | First (active) | Dilatation below the partograph line | Assess passage and passenger, consider oxytocin |
| Arrest of dilatation | First (active) | No change over about 4 h with adequate contractions | Evaluate for disproportion and augment |
| Arrest of descent | Second | No descent despite pushing: about 2 h (nullipara) or 1 h (multipara), plus 1 h with epidural | Assess for operative delivery or caesarean |
The first question is always whether the contractions are adequate, because a strong and frequent pattern that still fails to progress points to passage or passenger causes. Time limits differ between textbooks and protocols, so the examination answer should name the definition used and the reason for the choice.
Where the exam tries to catch you
Dystocia questions test whether the candidate names the pattern correctly and checks the passage and passenger before augmenting.
- Trap: calling every slow labour a prolonged latent phase Correct: the latent phase is the early slow phase, while a slow active phase is protraction, which is managed differently.
- Trap: starting oxytocin without assessing for cephalopelvic disproportion Correct: augmentation is safe only when the passage and passenger are adequate, so an obstructed labour needs assessment first.
- Trap: assuming arrest of descent always needs caesarean section Correct: a head in an adequate pelvis may descend with more time or assisted delivery, so the cause is assessed first.
Frequently asked questions
What is the difference between protraction and arrest of labour?
Protraction is slower-than-expected dilatation in the active phase, while arrest is a complete stop in progress. Both are dystocia patterns, and both are managed by assessing power, passage and passenger. Arrest is the more serious finding and usually prompts a firmer decision.
Which of the three Ps is the commonest cause of labour dystocia?
Power, meaning inadequate uterine contraction, is one of the commonest causes of labour dystocia in clinical practice. Passage and passenger problems are assessed separately. Textbooks differ on the exact proportions, so the examination answer names all three factors.
What defines a prolonged latent phase?
A prolonged latent phase is a latent phase that runs beyond the classic limits of about 20 hours in a nulliparous woman or 14 hours in a multiparous woman. Current guidance uses different thresholds, so the local protocol should be stated. Management includes reassessment and, where appropriate, analgesia or augmentation.
How long is arrest of descent usually defined as in the second stage?
Arrest of descent in the second stage is usually defined as no further descent despite adequate expulsive efforts, classically after about two hours in a nulliparous and one hour in a multiparous woman, with an extra hour allowed under epidural analgesia. ACOG allows up to three hours and two hours respectively, so the time limits vary by source. The finding prompts assessment for operative delivery or caesarean section.
What is the fourth P in labour dystocia?
The fourth P is psyche, the maternal emotional state and anxiety, which can affect the contraction pattern and labour progress. It is an additional consideration beyond power, passage and passenger. Support, reassurance and pain relief are part of management.