Obstetrics Simplified - Diaa
Labour is the process by which a viable foetus i.e. at the end of 28
weeks or more is expelled or is going to be expelled from the uterus.
Delivery means actual birth of the foetus.
The following criteria should be present to call it normal labour:
- Spontaneous expulsion,
- of a single,
- mature foetus,
- presented by vertex,
- through the birth canal,
- within a reasonable time (not less than 3 hours or more than 18
- without complications to the mother,
- or the foetus.
Cause of Onset of Labour
It is unknown but the following theories were postulated:
- Oestrogen theory:
- During pregnancy, most of the oestrogens are present in a binding
form. During the last trimester, more free oestrogen appears increasing
the excitability of the myometrium and prostaglandins synthesis.
- Progesterone withdrawal theory:
- Before labour, there is a drop in progesterone synthesis leading
to predominance of the excitatory action of oestrogens.
- Prostaglandins theory:
- Prostaglandins E2 and F2α are powerful stimulators of uterine
muscle activity. PGF2α was found to be increased in maternal and
foetal blood as well as the amniotic fluid late in pregnancy and
- Oxytocin theory:
- Although oxytocin is a powerful stimulator of uterine contraction, its natural role in onset of labour is doubtful. The secretion
of oxytocinase enzyme from the placenta is decreased near term due
to placental ischaemia leading to predominance of oxytocin’s action.
- Foetal cortisol theory:
- Increased cortisol production from the foetal adrenal gland
before labour may influence its onset by increasing oestrogen production
from the placenta.
- Uterine distension theory:
- Like any hollow organ in the body, when the uterus in distended
to a certain limit, it starts to contract to evacuate its contents.
This explains the preterm labour in case of multiple pregnancy and
- Stretch of the lower uterine segment:
- by the presenting part near term.
CLINICAL PICTURE OF LABOUR
Prodromal (pre-labour) stage
The following clinical manifestations may occur in the last weeks of
- It is falling forwards of the uterine fundus making the upper
abdomen looks like a shelf during standing position. This is due
to engagement of the head which brings the foetus perpendicular
to the pelvic inlet in the direction of pelvic axis.
- It is the relief of upper abdominal pressure symptoms as dyspnoea,
dyspepsia and palpitation due to:
- descent in the fundal level after engagement of the head
- shelfing of the uterus.
- Pelvic pressure symptoms:
- With engagement of the presenting part the following symptoms
- Frequency of micturition,
- rectal tenesmus and
- difficulty in walking.
- Increased vaginal discharge.
- False labour pain:
These are differentiated from true labour pain as follow:
True Labour Pain
False Labour Pain
Increase progressively in frequency, duration and intensity.
Pain is felt in the abdomen and radiating to the back.
Pain is felt mainly in the abdomen.
Progressive dilatation and effacement of the cervix.
No effect on the cervix.
Membranes are bulging during contractions.
No bulging of the membranes.
Not relieved by antispasmodics or sedatives.
Can be relieved by antispasmodics and sedatives.
Onset of Labour
It is characterised by:
- True labour pain.
- The show:
- It is an expelled cervical mucus plug tinged with blood from
ruptured small vessels as a result of separation of the membranes
from the lower uterine segment. Labour is usually starts several
hours to few days after show.
- Dilatation of the cervix:
- A closed cervix is a reliable sign that labour has not begun.
In multigravidae the cervix may admit the tip of the finger before
onset of labour.
- Formation of the bag of fore-waters:
- It bulges through the cervix and becomes tense during uterine
STAGES OF LABOUR
Labour is divided into four stages:
It is the stage of cervical dilatation.
Starts with the onset of true labour pain and
ends with full dilatation of the cervix i.e. 10 cm in diameter.
It takes about 10-14 hours in primigravida and
about 6-8 hours in multipara.
It is the stage of expulsion of the foetus.
Begins with full cervical dilatation and ends
with the delivery of the foetus.
Its duration is about 1 hour in primigravida and
½ hour in multipara.
It is the stage of expulsion of the placenta and
Begins after delivery of the foetus and ends with
expulsion of the placenta and membranes.
Its duration is about 10-20 minutes in both primi
It is the stage of early recovery.
Begins immediately after expulsion of the placenta
and membranes and lasts for one hour.
During which careful observation for the patient,
particularly for signs of postpartum haemorrhage is essential. Routine
uterine massage is usually done every 15 minutes during this period.
Causes of cervical dilatation
- Contraction and retraction of uterine musculature.
- Mechanical pressure by the forebag of waters, if membranes still
intact, or the presenting part, if they had ruptured. This in turn will
release more prostaglandins which stimulate uterine contractions and
- Softness of the cervix which has occurred during pregnancy facilitates
dilatation and effacement of the cervix.
Mechanism of cervical dilatation
- In primigravidas, the cervical canal dilates from above downwards
i.e. from the internal os downwards to the external os. So its length
shorts gradually from more than 2 cm to a thin rim of few millimetres
continuous with the lower uterine segment. This process is called effacement
and expressed in percentage so when we say effacement is 70% it means
that 70% of the cervical canal has been taken up.
- Dilatation of the cervix (external os) starts after complete effacement
of the cervix.
- In multigravidas, effacement and dilatation occur simultaneously.
- In normal presentation and position, the head is applied well to
the lower uterine segment dividing the amniotic sac by the girdle of
contact into a hindwaters above it containing the foetus and a forewaters
below it. This reduces the pressure in the forewaters preventing early
rupture of membranes. After full dilatation of the cervix the hind and
forewaters become one sac with increased pressure in the bag of forewaters
leading to its rupture.
Phases of cervical dilatation
- Latent phase:
- This is the first 3 cm of cervical dilatation which is slow
takes about 8 hours in nulliparae and 4 hours in multiparae.
- Active phase:
- It has 3 components:
- acceleration phase,
- maximum slope, and
- deceleration phase.
The phase of maximum slope is the most detectable and the two other phases
are of shorter duration and can be detected only by frequent vaginal examination.
The normal rate of cervical dilatation in active phase is 1.2 cm/ hour
in primigravidae and 1.5 cm/hour in multiparae. If the rate is < 1cm / hour
it is considered prolonged.
Delivery of the head
- It is continuous throughout labour particularly during the second
stage and caused by:
- Uterine contractions and retractions.
- The auxiliary forces which is bearing down brought by contraction
of the diaphragm and abdominal muscles.
- The unfolding of the foetus i.e. straightening of its body
due to contractions of the circular muscles of the uterus.
- The head normally engages in the oblique or transverse diameter
of the inlet.
- Increased flexion:
- As the atlanto-occipital joint is nearer to the occiput than
the sinciput, increased flexion of the head occurs when it meets
the pelvic floor according to the lever theory.
- Increased flexion results in:
- The suboccipito-bregmatic diameter (9.5 cm) passes through
the birth canal instead of the suboccipito-frontal diameter
- The part of the foetal head applied to the maternal passages
is like a ball with equal longitudinal and transverse diameters
as the suboccipito-bregmatic = biparietal = 9.5 cm. The circumference
of this ball is 30 cm.
- The occiput will meet the pelvic floor.
- Internal rotation:
- The rule is that the part of foetus meets the pelvic floor first
will rotate anteriorly. So that its movement is in the direction
of levator ani muscles (the main muscle of the pelvic floor) i.e.
downwards, forwards and inwards.
- In normal labour, the occiput which meets the pelvic floor first
rotates anteriorly 1/8 circle.
- The suboccipital region lies under the symphysis then by head
extension the vertex, forehead and face come out successively.
- The head is acted upon by 2 forces:
- the uterine contractions acting downwards and forwards.
- the pelvic floor resistance acting upwards and forwards
so the net result is forward direction i.e. extension of the
- After delivery, the head rotates 1/8 of a circle in the opposite
direction of internal rotation to undo the twist produced by it.
- External rotation:
- The shoulders enter the pelvis in the opposite oblique diameter
to that previously passed by the head. When the anterior shoulder
meets the pelvic floor it rotates anteriorly 1/8 of a circle. This
movement is transmitted to the head so it rotates 1/8 of a circle
in the same direction of restitution.
Delivery of the shoulder and body
The anterior shoulder hinges below the symphysis pubis and with continuous
descent the posterior shoulder is delivered first by lateral flexion of
the spines followed by anterior shoulder then the body.
After delivery of the foetus, the uterus continues to contract and retract.
As the placenta is inelastic, it starts to separate through the spongiosa
layer by one of the following mechanisms:
Schultze’s mechanism (80%)
- The central area of the placenta separates first and placenta is
delivered like an inverted umbrella so the foetal surface appears first
followed by the membranes containing small retroplacental clot.
- There is less blood loss and less liability for retention of fragments.
Duncan’s mechanism (20%)
- The lower edge of the placenta separates first and placenta is delivered
- There is more liability of bleeding and retained fragments.
The 3rd stage is composed of 3 phases:
- Placental separation.
- Placental descent.
- Placental expulsion.
PHYSIOLOGICAL EFFECTS OF LABOUR
On the Mother
- First stage:
- Second stage:
- Temperature: slight rise to 37.5oC.
- Pulse: increases up to 100/min.
- Blood pressure: systolic blood pressure may rise slightly due
to pain, anxiety and stress.
- Oedema and congestion of the conjuctiva.
- Minor injuries: to the birth canal and perineum may occur particularly
- Third stage:
- Blood loss from the placental site is 100-200 ml and from laceration
or episiotomy is 100 ml so the total average blood loss in normal
labour is 250 ml.
On the Foetus
The physiological gradual overlapping of the vault bones as the skull
is compressed during its passage in the birth canal.
One parietal bone overlaps the other and both overlap the occipital and
frontal bones so fontanelles are no more detectable. It is of a good value
in reducing the skull diameters but severe and / or rapid moulding is dangerous
as it may cause intracranial haemorrhage.
Degree of Moulding
Suture lines closed but no overlap.
Overlap of the bones but reducible.
Overlap of the bones but irreducible.
- It is a soft swelling of the most dependent part of the foetal head
occurs in prolonged labour before full cervical dilatation and after
rupture of the membranes.
- It is due to obstruction of the venous return from the lower part
of the scalp by the cervical ring.
- Large caput may:
- obscure the sutures and fontanelles making identification of
the position difficult. This can be overcomed by palpation
of the ear,
- give an impression that the head is lower than its true level.
- Artificial caput succedaneum (chignon): is induced during vacuum
- Caput succedaneum disappears spontaneously within hours to days
- As it is a vital manifestation, so it is not detected in intrauterine
The presence of caput indicates that:
- the foetus was living during labour,
- labour was prolonged and difficult,
- the attitude of foetal head during labour can be expected as caput
is present in the most dependant part of it.
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Edited by Aldo Campana,