Normal and Abnormal Labour Progress: Active Labour Definition, Partograph Use, Dystocia, and Second-Stage Abnormalities

Definitions: Stages and Phases of Labour

First Stage

The first stage spans onset of labour to full cervical dilatation (10 cm).

Active first-stage labour is defined as cervical dilatation $\geq$6 cm in the presence of regular uterine contractions. The upward revision from 4 cm reflects evidence that dilatation before 6 cm is physiologically slower; applying the older threshold leads to premature diagnosis of dystocia and avoidable caesarean section. (Note: NICE 2020 defines the active phase as 4-5 cm to full dilatation; the WHO suggests 5 cm; the contemporary obstetric consensus used in RANZCOG-aligned practice is $\geq$6 cm.)

Second Stage

Third Stage

Delivery of placenta and membranes - normally $<$10 minutes; up to 30 minutes without excessive bleeding before escalating to active management.

The Partograph and Cervicogram

Purpose

A graphical, real-time record of labour progress enabling early identification of deviation from expected norms. Components include:

• Cervical dilatation and fetal descent plotted against time
• Fetal heart rate
• Uterine contraction frequency and duration
• Maternal observations: pulse (hourly), BP and temperature (4-hourly), urine ketones and protein (4-hourly)
• Medications including oxytocin dose and rate

Alert and Action Lines

Vaginal examination is offered every 4 hours in active labour (or earlier if clinical concern). Slow progress is identified when dilatation is $<$2 cm over 4 hours (plot crosses to the right of the action line).

Limitations

• Based on Friedman-era nulliparous norms; may not reflect contemporary diverse populations
• Does not account for epidural analgesia, maternal BMI, or parity-specific variation
• Women with BMI $>$30 kg/m² have a physiologically longer latent-to-active transition (particularly before 6-7 cm); the main delay point in overweight women is 4-6 cm and in obese women before 7 cm - modified thresholds before intervening are warranted
• WHO recommends partograph use in resource-limited settings; its routine utility in high-income settings is under revision

Diagnosis of Failure to Progress - First Stage

Diagnostic Criteria

Active-phase protraction (traditional Friedman criteria): $<$1.2 cm/hour (nullipara), $<$1.5 cm/hour (multipara). Contemporary Obstetric Care Consensus criteria specify that slow but progressive first-stage labour alone is not an indication for caesarean section; arrest criteria (no dilatation $\geq$2 hours with adequate contractions, or no progress after 4 hours of adequate contractions / 6 hours of inadequate contractions despite oxytocin) should guide the decision.

Up to 80% of women with active-phase arrest have inadequate contractions ($<$180 Montevideo units); the majority respond to oxytocin augmentation.

Causes of Dystocia - The Three Ps

Powers: Uterine Inertia (Most Common)

Disproportion is intimately related to dystocia - adequate uterine activity must be established before diagnosing mechanical obstruction.

Passenger: Malposition and Malpresentation

Persistent OP position occurs in ~25% of cases where OP is diagnosed in labour. Adequate uterine activity corrects malposition in ~75% of OP presentations (long rotation 135° to OA). The anthropoid pelvis (AP diameter widest) is associated with higher risk of persistent OP. Deflexion and asynclitism with OP create relative disproportion compounded by inadequate uterine activity.

Passage: Cephalopelvic Disproportion (CPD)

Caldwell-Moloy pelvic classification: gynaecoid (50%), anthropoid (25%), android (20%), platypelloid (3%). Clinical relevance is limited (see below).

True CPD is a tenuous diagnosis: 50-75% of women delivered by caesarean for CPD subsequently deliver larger infants vaginally - reflecting the predominance of relative over absolute disproportion.

Clinical Pelvimetry - Limitations

• Manual assessment of the diagonal conjugate, transverse outlet, subpubic angle, sacral curve, and ischial spine prominence has high inter- and intra-observer variability
• Clinical assessment of pelvic shape is acknowledged to be inaccurate and rarely influences management
• CT and MRI pelvimetry provide precise measurements but have not been shown to improve outcomes and are not recommended for routine vertex presentations
• The only reliable test of pelvic adequacy is a trial of labour
• Absolute disproportion due to a contracted pelvis is now rare; most CPD is relative
• Clinical pelvimetry retains a limited role in vaginal breech delivery planning, though even here its predictive value is poor

Management of First-Stage Dystocia

Structured Approach

Amniotomy alone does not reliably shorten labour or reduce operative delivery rates; amniotomy combined with oxytocin reduces caesarean section risk (RR ~0.87) and shortens labour (~1.3 hours).

Oxytocin Augmentation

• Start at low dose (1-4 mU/min); titrate upward every 30 minutes
• Target: 3-4 contractions per 10 minutes, each lasting 40-60 seconds
• Continuous CTG mandatory
• Myometrial sensitivity to oxytocin increases as labour advances - dose may need to be reduced in the active phase to avoid hyperstimulation
• Oxytocin augmentation in multiparous women must only be initiated by the most senior obstetrician available; uterine rupture is a serious risk and augmentation should be approached with extreme caution
• Women with a previous uterine scar: oxytocin requires senior review; threshold for caesarean section should be lower

Special Considerations

Abnormal Second Stage

Duration Thresholds

Overall second-stage limits (without regional analgesia, from full dilatation): - Nulliparous: birth within 3 hours - Multiparous: birth within 2 hours

With regional analgesia: passive descent of at least 1 hour (possibly longer if the woman wishes and CTG is reassuring) is recommended before encouraging active pushing. With regional analgesia and a normal FHR pattern, birth should occur within 4 hours of full dilatation regardless of parity.

Management of Prolonged Second Stage

Oxytocin in the second stage: May be commenced in nulliparous women during the passive phase if contractions are inadequate, particularly with persistent OP. In multiparous women, use only after senior obstetrician review; extreme caution - uterine rupture risk. Do not augment multiparous women with confirmed brow or abnormal presentations without senior review.

Instrumental vaginal delivery: Consider when presenting part is at or below the ischial spines and other criteria are met. Delivery from mid-cavity (0 to +2 station) in OP position requires critical senior assessment of vaginal versus abdominal delivery.

Complications of Failure to Progress and Its Management

Counselling Points

• Explain diagnosis of slow progress in plain language with likely causative "P"
• Amniotomy and oxytocin: balanced explanation of benefits (shorter labour, reduced dystocia-related CS) and risks (increased contraction frequency, continuous monitoring requirement, possible FHR changes)
• Oxytocin does not guarantee vaginal birth - caesarean may still be required
• Upright positioning and mobility support progress where clinically safe
• Epidural analgesia may slow progress and alter pushing sensation; second-stage implications should be discussed
• Multiparous women: document specific counselling regarding uterine rupture risk with oxytocin
• Previous caesarean: individualised counselling regarding scar rupture risk with augmentation

Medicolegal and Documentation Considerations

• Accurate contemporaneous partograph documentation is essential; deviations from normal progress and clinical decisions (including who was consulted and when) must be recorded
• Oxytocin augmentation in multiparous women and those with uterine scars mandates involvement of a senior obstetrician - failure to escalate is a recognised source of adverse outcomes
• Amniotomy and oxytocin require documented informed consent including discussion of alternatives
• Both under-intervention (prolonged obstructed labour) and over-intervention (premature CS before adequate trial of augmentation) carry medicolegal risk
• Any CTG deterioration during oxytocin infusion must prompt prompt action; failure to respond to FHR changes during augmentation is a recurring theme in adverse outcome reviews
• Clear verbal and written handover at shift changes during prolonged labour is a patient safety imperative

Summary Table: Key Diagnostic Thresholds