Explain labour steps

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stages of labour obstetrics clinical steps mechanism 2024

Here is a complete, clinically structured explanation of the stages and mechanism of labour:

Stages of Labour

Labour is the process by which the uterus expels the fetus and placenta through a series of progressive, coordinated physiological events. It is divided into 4 stages (some classical texts describe 3 stages, with stage 1 subdivided).

Stage 0 - Prelabour / Prodromal Phase

Before true labour begins, several preparatory changes occur:

Cervical ripening: the cervix softens, shortens (effaces), and begins to dilate due to prostaglandins (PGE2, PGF2α) and relaxin
Braxton Hicks contractions (irregular, painless) become more frequent
The fetal presenting part descends (engages) into the pelvis - this is called lightening
Show: a blood-tinged mucus plug is expelled from the cervix

True labour is defined as regular, painful uterine contractions causing progressive cervical effacement and dilatation.

First Stage - Cervical Dilatation (Onset of labour to full dilatation at 10 cm)

The first stage is the longest and is subdivided into two phases:

Latent Phase

From onset of labour to approximately 6 cm dilatation
Contractions: irregular to regular, 2-3 per 10 minutes, mild-moderate intensity
Cervix effaces completely and dilates slowly
Normal duration: up to 20 hours in nulliparas, up to 14 hours in multiparas
Prolonged latent phase: >20 hours in nulliparas, >14 hours in multiparas

Active Phase

From 6 cm to full dilatation (10 cm)
Contractions: strong, 3-5 per 10 minutes, lasting 45-60 seconds
Expected rate of dilatation: at least 1 cm/hour (historical Friedman curve); current ACOG CPG No. 8 (2024) recognizes that normal progress may be slower in contemporary populations
Transition: the last 2-3 cm (8-10 cm) - the most intense part; may be accompanied by nausea, shaking, pressure

Monitoring during first stage:

Partograph (WHO) to plot cervical dilatation vs. time
Fetal heart rate auscultation or CTG
Vaginal examination every 4 hours (or sooner if indicated)
Assessment of descent, station, position of the presenting part

Second Stage - Expulsion (Full dilatation to delivery of the baby)

Begins when the cervix is fully dilated (10 cm) and ends with delivery of the fetus.

Passive phase (Passive descent):

Fetal head descends with contractions before the urge to push
Duration varies; epidural analgesia prolongs this phase

Active phase (Active pushing):

Mother begins pushing with contractions (bearing down / Valsalva)
Descent, rotation, and delivery occur

Normal duration:

Nulliparas: up to 3 hours (4 hours with epidural)
Multiparas: up to 2 hours (3 hours with epidural)

Cardinal Movements (Mechanism of Labour)

These 7 movements describe how the fetal head navigates the maternal pelvis - they overlap and are part of a continuous process:

#	Movement	What Happens
1	Engagement	Biparietal diameter (BPD) passes through the pelvic inlet; station 0
2	Descent	Continuous downward movement of the presenting part throughout labour
3	Flexion	Chin flexes onto chest - smaller suboccipitobregmatic diameter presents (9.5 cm)
4	Internal rotation	Occiput rotates anteriorly to face the pubic symphysis (OA position) to pass through the midpelvis
5	Extension	Head extends as it passes under the pubic arch; delivers by extension - face, brow, then occiput
6	Restitution & External rotation	Head realigns with shoulders; external rotation as shoulders rotate to AP diameter of outlet
7	Expulsion	Anterior shoulder delivers under pubis, posterior shoulder sweeps over perineum; trunk and legs follow

Third Stage - Delivery of the Placenta (From delivery of baby to delivery of placenta)

Active management (preferred): oxytocin 10 IU IM immediately after birth, controlled cord traction (Brandt-Andrews manoeuvre), uterine massage
Signs of placental separation: Brandt's signs
- Gush of blood
- Lengthening of the umbilical cord
- Uterus rises and becomes globular (Calkin's sign)
Normal duration: ≤30 minutes; >30 minutes = retained placenta
Deliver placenta by controlled cord traction; examine for completeness

Active Management of Third Stage of Labour (AMTSL) reduces the risk of postpartum haemorrhage (PPH) by ~66%.

Fourth Stage - Recovery (First 1-2 hours postpartum)

Close monitoring for PPH (most common complication)
Uterine fundal massage and assessment of tone every 15 minutes
Vital signs monitoring
Perineal repair if laceration or episiotomy occurred
Skin-to-skin contact and initiation of breastfeeding

Degrees of perineal tears:

1st degree: skin/mucosa only
2nd degree: perineal muscles (not sphincter)
3rd degree: extends into external anal sphincter
4th degree: through anal sphincter into rectal mucosa

Summary Table

Stage	Start	End	Normal Duration (Nullipara)
1st (latent)	True labour onset	6 cm dilatation	Up to 20 hours
1st (active)	6 cm	10 cm (full)	Variable; ~1 cm/hr
2nd	Full dilatation	Delivery of baby	Up to 3 hours
3rd	Delivery of baby	Delivery of placenta	Up to 30 minutes
4th	Delivery of placenta	2 hours postpartum	1-2 hours monitoring

Key references:

ACOG Clinical Practice Guideline No. 8 (2024) - First and Second Stage Labour Management
Medscape: Normal Labour and Delivery - Cardinal movements and stages
Park's Textbook of Preventive and Social Medicine - Care during labour and childbirth

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