Give a descriptiptive answer on normal labour, stages of labour and obstructed labour

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normal labour stages of labour obstructed labour clinical management 2024

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Normal Labour, Stages of Labour, and Obstructed Labour

1. Normal Labour - Definition and Prerequisites

Normal (physiological) labour is defined as the process by which regular, spontaneous uterine contractions cause progressive cervical effacement and dilatation, ultimately resulting in the expulsion of the fetus and placenta through the birth canal.

WHO criteria for normal labour:

Spontaneous onset between 37-42 completed weeks of gestation
Single fetus in cephalic (vertex) presentation
No complications before or during labour
Spontaneous vaginal delivery
Healthy mother and baby at the end

The "Three Ps" Framework

Labour progress depends on the interaction of three key factors:

Factor	Components
Powers	Uterine contractions + maternal bearing-down efforts (secondary powers)
Passage	Bony pelvis (inlet, midpelvis, outlet) + soft tissues (cervix, vagina, perineum)
Passenger	Fetus - size, presentation, position, lie, and attitude

2. Physiology of Uterine Contractions

Contractions originate from the pacemaker region at the cornual junction of the uterus. They have:

Fundal dominance: the contraction starts at the fundus and sweeps down
Triple descending gradient: the contraction is strongest and longest at the fundus, progressively weakening downward
Polarity: the upper uterine segment (UUS) contracts and retracts; the lower uterine segment (LUS) dilates and thins passively

As labour progresses, the retraction ring (physiological retraction ring / Bandl's ring in pathology) forms at the junction of the UUS and LUS.

3. Stages of Labour

Labour is classically divided into three stages (some include a fourth).

Stage 1 - Cervical Effacement and Dilatation

Definition: From the onset of true labour to full cervical dilatation (10 cm).

Divided into two phases:

a) Latent Phase

Cervix effaces and dilates from 0 to 4 cm (Friedman) or 0-6 cm (newer ACOG 2014 criteria)
Irregular, mild contractions that gradually become more regular
Duration: up to 20 hours in nulliparae, up to 14 hours in multiparae
Prolonged latent phase: >20 hours (nullipara) or >14 hours (multipara)

b) Active Phase

Cervical dilatation from 4-6 cm (or 6 cm by ACOG) to 10 cm
Regular, strong contractions: typically 3-5 per 10 minutes, lasting 45-60 seconds, intensity 50-75 mmHg
Friedman's curve - expected dilatation rate: ≥1.2 cm/hour (nullipara) and ≥1.5 cm/hour (multipara)
More recent WHO/ACOG data shows: ≥1 cm/hour after 6 cm dilatation
Fetal descent begins in this phase, particularly in multiparae

Physiological changes in Stage 1:

Cervix effaces (shortens) before dilating (especially in nulliparae)
Forewaters (bag of membranes) may rupture spontaneously ("show")
Bloody show (pink-stained mucus) from displacement of cervical mucus plug
Engagement of fetal head typically precedes labour onset in nulliparae

Stage 2 - Delivery of the Fetus

Definition: From full cervical dilatation (10 cm) to complete delivery of the baby.

Duration:

Nullipara: up to 2 hours (3 hours with epidural)
Multipara: up to 1 hour (2 hours with epidural)
Prolonged Stage 2: exceeding these limits

Mechanism of Normal Labour (Cardinal Movements)

In a well-flexed cephalic vertex presentation in a gynecoid pelvis, the fetus undergoes a series of movements:

Movement	Description
1. Engagement	Biparietal diameter (BPD) passes through the pelvic inlet; head enters at the transverse or oblique diameter
2. Descent	Progressive downward movement of the fetal presenting part throughout all stages
3. Flexion	Head flexes so chin approaches chest; suboccipito-bregmatic (9.5 cm) replaces larger diameters
4. Internal Rotation	Head rotates from transverse/oblique to anteroposterior in the midpelvis; occiput comes to lie under the symphysis pubis (OA position)
5. Extension	Head extends under the pubic symphysis; occiput, bregma, face, and chin successively sweep over the perineum
6. Restitution	After delivery of head, it rotates back to its natural alignment with the shoulders
7. External Rotation	Shoulders rotate internally in the pelvis; the head (externally) rotates further to the transverse
8. Expulsion	Anterior shoulder delivers first under the symphysis, then posterior shoulder, then body by lateral flexion

Monitoring in Stage 2:

Fetal heart rate (FHR) monitoring - auscultate after every contraction, or CTG continuously for high-risk
Maternal vital signs, progress of descent (station)
Perineal management - controlled delivery of head, episiotomy if indicated

Stage 3 - Delivery of the Placenta

Definition: From delivery of the baby to expulsion of the placenta and membranes.

Duration: Normally within 30 minutes; prolonged if >30 minutes without active management.

Phases of placental separation:

Contraction of uterus after fetal delivery - uterus becomes globular and hard
Gush of blood as retroplacental hematoma forms
Lengthening of cord as placenta descends
Expulsion of placenta - Schultze mechanism (central separation, shiny fetal surface first, ~80%) or Matthews-Duncan mechanism (marginal separation, maternal surface first, ~20%)

Active Management of Third Stage (AMTSL):

Oxytocin 10 IU IM/IV within 1 minute of birth (first-line agent)
Controlled cord traction (Brandt-Andrews manoeuvre) after signs of separation
Uterine massage after placenta delivery
Reduces postpartum haemorrhage (PPH) risk by ~60%

Signs of placental separation:

Uterus rises and becomes globular (Calkin's sign)
Sudden gush of blood
Cord lengthens at vulva
Fundus rises in the abdomen

Stage 4 (Immediate Postpartum Period)

Not universally classified as a formal stage, but clinically important
The first 1-2 hours following placental delivery
Monitored for primary PPH, uterine atony, perineal lacerations, vital signs
Uterus should remain firmly contracted (size of a grapefruit at umbilicus level)

4. Monitoring Labour - The Partograph

The partograph (WHO partograph) is the standard tool for monitoring labour:

Records: cervical dilatation, fetal descent, fetal heart rate, uterine contractions, maternal vitals, medications
Alert line: expected normal progress (1 cm/hr) from active phase onset
Action line: 4 hours to the right of the alert line
Crossing the action line signals the need for intervention

5. Obstructed Labour

Definition

Obstructed labour occurs when, despite strong uterine contractions, the fetus cannot descend through the birth canal due to a mechanical obstruction. The presenting part fails to advance despite adequate (or seemingly adequate) uterine powers.

It is distinct from "prolonged labour" (which is time-based) - obstruction is a mechanical failure of the passenger/passage relationship.

Causes of Obstruction

Fetal causes (Passenger):

Malpresentation: brow presentation (commonest malpresentation causing obstruction), face presentation (mentoposterior), shoulder presentation (transverse lie, completely obstructs)
Malposition: persistent occipito-posterior (OP), deep transverse arrest
Large baby (absolute or relative macrosomia)
Hydrocephalus, fetal anomalies
Locked twins

Maternal causes (Passage):

Contracted pelvis (pelvic inlet, midpelvis, or outlet contraction)
- Causes: rickets, malnutrition, pelvic fractures
Cephalopelvic disproportion (CPD)
Cervical fibroid, ovarian cyst in the pelvis
Previous pelvic surgery/scar
Atresia or stenosis of the vagina/cervix

Clinical Features of Obstructed Labour

General signs:

Exhausted, anxious, dehydrated mother
Fever, tachycardia
Ketonuria, oliguria
Prolonged duration of labour

Abdominal signs:

Uterus tightly moulded over the fetus (loss of fetal parts palpability)
Bandl's pathological retraction ring: a palpable transverse groove/band across the lower abdomen at the junction of the UUS and LUS, indicating impending uterine rupture. The UUS becomes thick and short while the LUS becomes thin and stretched. This is a danger sign.
Round ligaments tense and tender (appearing as visible cords)
LUS tender on palpation, may show "hourglass" shape

Vaginal signs:

Presenting part deeply impacted, immovable
Excessive caput succedaneum (scalp oedema) and moulding (overlapping of skull bones) - Grade 3 moulding (bones overriding and not reducible) is ominous
Oedematous, congested cervix and vagina
Foetid liquor if membranes ruptured for >18 hours (risk of chorioamnionitis)

Bladder signs:

Urinary retention or haematuria (from bladder compression between fetal head and symphysis pubis) - indicates impending vesicovaginal fistula (VVF)

Grades of Moulding

Grade	Finding
+	Bones touching but not overlapping
++	Bones overlapping but easily reducible
+++	Bones overlapping and not reducible - OBSTRUCTED

Complications of Obstructed Labour

Maternal complications:

Complication	Mechanism
Uterine rupture	UUS/LUS tears, catastrophic haemorrhage, life-threatening
Vesicovaginal fistula (VVF)	Bladder compressed between fetal head and symphysis; ischaemic necrosis
Rectovaginal fistula (RVF)	Less common, posterior compartment compression
Postpartum haemorrhage	Uterine atony, tears, ruptured uterus
Sepsis/puerperal infection	Prolonged labour, ruptured membranes, multiple VEs
Maternal death	From rupture, haemorrhage, or sepsis

Fetal complications:

Fresh stillbirth (the most common outcome in neglected cases)
Birth asphyxia - hypoxic ischaemic encephalopathy (HIE)
Tentorial tears, intracranial haemorrhage from moulding
Severe caput and moulding

Management of Obstructed Labour

Immediate resuscitation:

IV access - two large-bore cannulae
IV fluids (Ringer's lactate/crystalloid) for hydration and to correct dehydration/shock
Catheterize bladder (relieves compression, monitors urine output)
Broad-spectrum antibiotics (ampicillin + gentamicin + metronidazole)
Blood grouping and cross-matching

Definitive management (depends on cause, stage, and fetal viability):

Situation	Management
Live fetus, vaginal delivery not feasible	Emergency caesarean section (most common intervention)
Dead fetus, vaginal delivery possible	Destructive/instrumental operations (craniotomy, decapitation) - in resource-limited settings
Brow presentation	C-section (brow cannot deliver vaginally unless it converts)
Face - mentoanterior	Vaginal delivery possible; mentoposterior requires C-section
Shoulder presentation / transverse lie	C-section
Deep transverse arrest	Vacuum/forceps if criteria met; otherwise C-section

Note on Bandl's Ring: Once a pathological retraction ring is identified, caesarean section must be performed immediately. Attempting further vaginal manoeuvres risks complete uterine rupture.

Prevention of Obstructed Labour

Skilled birth attendance
Antenatal care with pelvic assessment
Use of the partograph with early recognition of poor progress
Timely referral from community/primary care
Addressing CPD early (elective C-section if trial of labour unsafe)
Management of malpresentation before/early in labour (ECV for breech)

Summary Table - Stages at a Glance

Stage	Definition	Normal Duration (Nullipara / Multipara)	Key Events
Stage 1 (Latent)	Onset of labour to 4-6 cm dilatation	Up to 20 hrs / 14 hrs	Effacement, slow dilatation
Stage 1 (Active)	4-6 cm to full dilatation (10 cm)	6-12 hrs / 4-6 hrs	Rapid dilatation, descent begins
Stage 2	Full dilatation to birth of baby	Up to 2 hrs / up to 1 hr	Cardinal movements, delivery
Stage 3	Birth of baby to placental delivery	Up to 30 min	Placental separation, expulsion
Stage 4	First 1-2 hrs postpartum	1-2 hours	Monitoring for PPH, involution

Sources: Merck Manual - Management of Normal Labor | NCBI - Normal Labor Physiology | NCBI - Abnormal Labor

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