Labour is the process by which regular painful contractions bring about effacement, ie shortening or thinning of tissue, and dilatation of the cervix and decent of the presenting part.
This ultimately leads to expulsion of the fetus and the placenta from the mother.
The onset of labour is brought about by regular contractions, which result in progressive cervical change.

Pathophysiology of Labour

Progesterone maintains uterine quiescence (suppress PGs, prevent Oxytocin release)
Oestrogen opposes the action of progesterone.
Fetally produced cortisol may also contribute to the conversion of progesterone to oestrogen

Myometrial activity: 4 phases
Phase 0 inhibitors active
Phase 1 myometrial activation
Phase 2 stimulating- E2, Pg, Oxytocin
Phase 3 involution (after expulsion of placenta)

Mechanism of Labour

7 cardinal movements of labour:

Think of the following according to the 3 altered shapes of the pelvic canal:

1 Engagement- when the widest part of the presenting part has passed successfully through the inlet. Occurs in vast majority prior labour. If more than 2 fifths of the fetal head if palpable abdominally, the head is not yet engaged.

2 Descent- this is secondary to uterine action, helped by voluntary use of abdominal musculature and the Valsalva manoeuvre (pushing) in the active phase of the second stage of labour.
3 Flexion- happens as head descends into the narrower mid-cavity. Important in minimizing the presenting diameter of the fetal head and happens due to the surrounding structures.

4 Internal rotation- so that the sagittal suture lies in the AP diameter of the pelvic outlet (the widest diameter) on reaching the sloping gutter of the levator ani muscles. OP position persistence is associated with extension of the fetal head and possibly obstructed labour or need for Caesarean section.
5 Extension- the well-flexed head now extends and the occiput escapes from underneath the symphysis pubis and distends the vulva- ‘crowning’ of the head. The symphysis pubis acts as a fulcrum point as the bregma, face and chin appear in succession over the posterior vaginal opening and perineal body. This extension and movement minimize soft-tissue trauma by utilizing the smallest diameters of the head for the birth. This extension and movement minimize soft-tissue trauma by utilizin ghte smallest diameters of the head for the birth.

6 Restitution/External rotation- when the head is delivering, the occiput is directly anterior. The slight rotation of the occiput through one-eighth of a circle is called restitution.
External rotation- shoulders rotate into the direct AP plane.
7 Expulsion

The 3Ps:
Powers- uterine contractions, 3-5/10min
Passenger- size, lie, presentation, attitude (flexion etc), position, station, fetal abn

The Three Stages of Labour

  • Onset - full dilatation of the cervix (10cm)
Latent phase (time between onset of labour and 3-4cm dilatation; may come and go; slow cervical dilatation).
Cervix becomes ‘fully effaced’. Effacement is a process by which the cervix shortens in length as it becomes included into the lower segment of the uterus.
Active phase (time between end of the latent phase and full dilatation; rapid dilatation, minimum cervical dilatation should be 1cm/h- normally 2-3cm/hour)
Lasting between 2-6 hours (shorter in multiparous women).

Transition: between stages 1 and 2; change in maternal behaviour
  • Full dilatation of the cervix - delivery of the fetus or foetuses.
Passive phase (no maternal urge to push and fetal head is still relatively high in the pelvis.)
Active second stage (maternal urge to push because fetal head is low, causing a reflex need to ‘bear down’.
Should last no longer than 2 hours. Head descends on pelvic floor, maintain flexion; crowning, control delivery of head is important at this stage
Epidural anaesthetia may influence length and management of this stage of labour

  • Time from delivery of fetus until delivery of the placenta.
The placenta is usually delivered within a few minutes of the birth of the baby.
A third stage lasting more than 30minutes should be considered abnormal.
Given syntocin
clamp and cut cord

Monitoring in Labour

Vaginal Exam in Labour
  • Effacement
  • Dilatation*
  • Station +/- ischial spine
  • Position (fetal)
  • Presenting part (diamond vs triangle)**
[+] regular exam
[+] FHR monitor/CTG

*Assessing cervical dilatation: The Bishop Score (3 pts x 5 criteria)
    • Dilatation of cervix
    • Consistency of cervix
    • Length of cervical canal
    • Position of cervix
    • Station of presenting part

    • Assessing presenting part

Induction of Labour (IOL)

Syntocin (oxytocin)
if cervix not favourable, use Pgs
CTG to monitor
Normal CTG:
1) baseline fetal heart rate betwteen 110-160bpm
2) normal baseline variability
3) accelerations: a minimum of 2 accelerations within a 20 min period is required)
4) no decelerations

Pain Relief in labour

1. NO gas
2. pethidine IM injection
3. epidural

Mx of Labour

Normal labour
1. education, support, prep
2. review, antenatal Hx
3. evaluation, BP, HR, FHR, urinalysis

Stage 1 FHR/15min
Stage 2 FHR/contraction
[+] CTG if indicated

1. education, support, prep
2. review, antenatal Hx
3. evaluation, BP, HR, FHR, urinalysis

Abnormal Labour
Stage 1 FHR/15min
Rx: Amniotomy
Syntocin (in primigravida; caution in multigravida as uterus may not stand strong contractions)

Stage 2
Arrest of descent >3 hours
arrest of descent without epidural > 2 hours
Rx: fluid resuscitation, reposition, forceps delivery (if presenting part lower than ischial spine)

Stage 3
should be less than 30min-1hour
N.B. The empty contracted uterus will NOT bleed
N.B. Routine active Mx of 3rd stage reduces maternal morbidity (syntocin to contract uterus and expel placenta)

Neonatal Assessment

APGAR score is recorded at 1 and 5 minutes
appearance, pulse/RR, grimace, Active, Resp.

Major causes of death in Labour


The Placenta

cytotorphoblast and syncial trophoblast
Day 5 implantation

Immune: prevent rejection of the fetal allograft
Oxygen/nutrition/waste product transfer
Endocrine (produce betaHCG, steroid homrones)

Placental praevia
Placental abruption

Antepartum Haemorrhage
= bleeding after 20 weeks until end of 2nd stage
Causes of antepartum haemorrhage include plaenta praevia (30%), placenta abruption (20%), other (50%)

painless (praevia) vs painful (abruption)
tender-less (praevia) vs tender (abruption)

U/S, Hb, Group and hold
Kleihauer Test

Rescuscitate and deliver (only if maternal or fetal compliance)
Anti-D if woman is Rhesus negative

Placental Praevia
underlying/prominent to itnernal cervical os

4:1,000 RF: