What are the stages of labour, their per‑vaginal examination findings, and the fetal head station in each stage?

Stages of Labour with Per Vaginum Findings and Station of Head

First Stage of Labour

The first stage of labour extends from the onset of regular contractions to complete cervical dilatation (10 cm) and is divided into latent and active phases, with the active phase beginning when cervical dilatation accelerates regardless of specific centimeter measurement. 1

Latent Phase

• Cervical findings: Progressive effacement and slow dilatation from 0 cm to the point where dilatation rate accelerates (typically 3-5 cm, but variable) 1
• Station: Fetal head typically remains high, often at -3 to -2 station (3-2 cm above ischial spines) 2
• Duration: Highly variable; can last hours to days 1
• Key diagnostic point: Identified by flat, slow cervical dilatation rate on serial examinations 1

Active Phase

The active phase is diagnosed solely by an accelerating cervical dilatation rate detected through serial vaginal examinations performed at least every 2 hours, not by reaching any specific centimeter of dilatation. 1

Acceleration Phase

• Cervical findings: Rapid increase in dilatation rate, steepest between 5-6 cm 1
• Normal dilatation rates: ≥1.2 cm/hour for nulliparous women; ≥1.5 cm/hour for multiparous women 1
• Station: Progressive descent begins; head typically moves from -2 to 0 station (at ischial spines level) 2
• Fetal head position: Most commonly occipital transverse in early active phase 3

Maximum Slope (Phase of Maximum Dilatation)

• Cervical findings: Linear, steady dilatation at maximum rate (≥1.2 cm/h nulliparous, ≥1.5 cm/h multiparous) 1
• Station: Continued descent from 0 to +1 station 2
• Cervical retraction: Occurs along the transverse plane of the fetal head 4

Deceleration Phase

• Cervical findings: Apparent slowing of dilatation from approximately 8-9 cm to complete dilatation (10 cm) 4
• Station: Significant descent must occur; head typically at +1 to +2 station 4
• Clinical significance: Terminal cervical dilatation will not occur unless fetal descent also takes place 4
• Mechanism: Cervical retraction "turns the corner" as it retracts cephalad along the fetal head, creating apparent slowing despite continuous linear retraction 4
• Duration: Normal duration ≤2-3 hours in nulliparous women, ≤1 hour in multiparous women 1
• Warning sign: Prolonged deceleration phase strongly suggests cephalopelvic disproportion and predicts second-stage abnormalities and shoulder dystocia risk 4

Critical pitfall: A dilatation rate of 0.6 cm/hour is too slow to represent true active labour and most likely indicates the patient remains in latent phase, not a protracted active phase. 1

Second Stage of Labour

The second stage extends from complete cervical dilatation (10 cm) to delivery of the fetus. 5

Per Vaginum Findings

• Cervical findings: Complete dilatation at 10 cm (or diameter matching fetal head size—smaller in preterm births, larger with macrosomia or hydrocephalus) 4
• Station progression: Descent from +2 through +3 to crowning 5
• Fetal head rotation: 37.1% of occipital transverse positions rotate to anterior during active phase; 28.6% rotate during second stage 3
• Average rotation: 62.6° from occipital transverse to anterior position 3

Normal Descent Patterns

• Assessment method: Progress measured by change in fetal station as a function of time, not just duration 5
• Ultrasound correlation: When angle of progression (AOP) <95°, 100% are occipital transverse; when AOP ≥125°, 66.7% are occipital anterior 3

Abnormal Patterns to Recognize

• Protracted descent: Slower than expected descent rate 5
• Arrest of descent: No change in station despite adequate time and contractions 5
• Failure of descent: Inadequate descent from the outset 5
• All three patterns: Strongly associated with cephalopelvic disproportion, maternal obesity, uterine infection, excessive sedation, and fetal malpositions 5

Duration Guidelines

• WHO recommendation: Allow 2-3 hours for second stage 1

Third Stage of Labour

The third stage extends from delivery of the fetus to expulsion of the placenta. 1

Per Vaginum Findings

• Cervical findings: Cervix begins to contract after fetal delivery 1
• Station: Not applicable (fetus delivered) 1
• Signs of placental separation: Cord lengthening, gush of blood, uterine fundus rises and becomes firm 1

Management

• Active management: Uterotonic prophylaxis (oxytocin + ergometrine, oxytocin + misoprostol, or carbetocin), delayed cord clamping (~3 minutes), controlled cord traction 1
• Duration: Up to 1 hour if not actively managed 1

Station Assessment Throughout Labour

Station describes the relationship of the fetal skull's distal part to the maternal ischial spines, measured in centimeters above (-) or below (+) this landmark. 5, 6

Station Scale

• -5 to -3: Fetal head floating, not engaged (typical latent phase) 2
• -2 to 0: Progressive engagement and descent (typical active phase) 2
• 0 (at spines): Engagement confirmed 2
• +1 to +2: Active descent (late first stage/deceleration phase) 2
• +3 to crowning: Second stage descent to delivery 5

Key Clinical Correlation

• Linear relationship: Station increases progressively with cervical dilatation during first stage 2
• Range: At any given dilatation, the 5th-95th percentile range of station spans approximately 3-4 cm 2
• Ultrasound advantage: Objective measurement via head-perineum distance, angle of progression, and progression distance provides more accurate assessment than digital examination alone 7, 6