physiology labour.pptx

PHYSIOLOGY OF
LABOUR
Group 13
WAN SALWANE BT MEOR
KHORIDI
YONG KET MEE
ZAHIRAH BT NASTU
ZUHANA BT ALI

Learning Objective:
 At the end of the learning session, the
student should be able to :
Define first stage of labour
Explain the normal labour
Explain the physiological changes
during the first stage of labour
Explain the stage of labour

Defination of Normal Labour
 The World Health Organization (WHO)
defines normal birth as: "spontaneous
in onset, low-risk at the start of labour
and remaining so throughout labour
and delivery.
 The infant is born spontaneously in the
vertex position between 37 and 42
completed weeks of pregnancy.

Defination Of First Stage of
Labour
 The first stage begins with the onset of
contraction that cause progressive changes
in the cervix and ends when this cervix is fully
dilated.
Primi - 1cm /hour, < 12 hours
Multi - 1.5cm / hour, 8 hour
 This stage can divided into two phases:
1) Early ( Latent) labour
2) Active labour

The onset of spontaneous normal
labour
Hormonal factors:
 Oestrogen
- A woman will produce more oestrogen during
pregnancy .
- Increase in oestrogen during pregnancy
enables
the uterus and placenta to improve
vascularization, transfer nutrients, and

- Helping the fetus develop and mature.
- Oestrogen levels increase steadily
during pregnancy and reach their peak
in the third trimester.
- Oestrogen level will keep on increase
to enable the uterus contract while
near to birth.

- High level of oestrogen allow
myometrium to be more sensitive
towards oxytocin.
- Oestrogen will drop , enable prolaction
to stimulate the mammary gland to
produce milk after birth.

 Progesterone
- Progesterone levels also are high
during pregnancy.
- The changes in progesterone cause a
laxity or loosening of ligaments and
joints throughout the body.

- Progesterone plays an important role in
the development of the foetus;
stimulates the growth of maternal breast
tissue; prevents lactation; and
strengthens the pelvic wall muscles in
preparation for labour.
- The level of progesterone in the body
steadily rises throughout pregnancy
until labour occurs and the baby is born.
- Progesterone will fall rapidly and
significant to enable the uterus to

 High level of progesterone inhibit
constriction of myometrium.

 Oxytocin
- Oxytocin levels rise at the onset of
labour, causing regular contractions of
the womb and abdominal muscles.
- Oxytocin induced contractions become
stronger and more frequent without the
influence of progesterone and
oestrogen, which at high levels prevent
labour.

- Oxytocin, along with other hormones,
stimulates ripening of the cervix leading
to successive dilation during labour.
- Oxytocin, with the help of the high levels
of oestrogen, causes the release of a
group of hormones, known as
prostaglandins, which may play a role in
ripening of the cervix.

 Prostaglandins:
- Produced by almost all nucleated cells
and synthesized in the cell from the
essential fatty acids (EFAs).
- Prostaglandins E2 and F2a are powerful
stimulators of uterine muscle cavity.
- PGF2a was found to be increase in
maternal and foetal blood as well as the
amniotic fluid late in pregnancy and
during labour.

 Relaxin:
- Levels of relaxin also increase rapidly
during labour.
- This aids the lengthening and softening
of the cervix.
- Relax the muscles of the pelvis so that
the baby can pass through the mother's
hips

Featal Cortisol
.
 Increase cortisol production from the
fetal adrenal gland before labour may
influence its onset by increasing
oestrogen production from the placenta.

Mechanical changes
 Stretch of the uterine muscle
- Increases contractility
▫ Fetal movements
 Stretch of the cervix
- Increases contractility (reflex)
- Membrane sweeping & rupture
- Fetal head
- Positive feedback mechanism

Positive feedback
mechanism

Initiation of Labor
Baby moves
deeper into
mother’s birth
canal

Pressoreceptors in cervix
of uterus excited

Afferent impulses
to hypothalamus

Hypothalamus sends
efferent impulses to
posterior pituitary, where
oxytocin is stored

Posterior pituitary releases
oxytocin to blood; oxytocin
targets mother’s uterine
muscle

Uterus responds
by contracting
more vigorously
.
Positive feedback
mechanism continues
to cycle until interrupted
by birth of baby

 True Labour
 Regular
contraction
“ Show”
Progressive
dilatation and
effacement of
cervix.
 False Labour
Irregular
contraction
No “Show”
No progressive
dilatation or
effacement cervix.

Physiology of The First Stage
Labour
1. Uterine Action
2. Mechanical Factor

Fundal Dominance
 Each uterine contraction commences
in the fundus near one of the cornua
and spreads across and downwards.
 The contraction last longest in the
fundus,
it is also most intense.

 The peak is reached simultaneously
over the whole uterus and the
contraction fades from all part
together.
 Permit the cervix to dilate and the
strongly contracting fundus to
eventually expel the fetus at the end of
labour.

Polarity
 Polarity is the term used to described
the neuromuscular hormony that prevails
between the two poles or segment of the
uterus throughout labour.
 During each uterine contraction, these
two poles act harmoniously.

 The upper pole contracts strongly and
retracts to expel the fetus.
 The lower pole contract slightly and
dilates to allow expulsion to take place.
 If polarity is disorganized then the
progress of labour is inhibited.

Intensity and Resting Tone
 Before labour become established,
uterine contraction may occur every 15 -
20 minutes, lasting about 30 seconds.
The contraction usually occur with
rhythmic regularity.

 Gradually lessen while the length and
strength gradually intensifies through the
latent phase and into the active phase of
the first stage of labour.
The contraction may occur at 2-3 minute
interval, last for 50- 60 second.

Formation of Upper And Lower
Uterine Segment
 The upper uterine segment, having been
formed from the body of the fundus, is
mainly concerned with contraction and
retraction.
 It is thick and muscular.
 The lower uterine segment is formed of the
isthmus and the cervix, and is about 8-
10cm in length.

 The lower segment is prepare for
distension and dilatation.
 The muscle content reduces from the
fundus to the cervix, where it is thinner.
 When the labour begins, the retracted
longitudinal fibres in the lower segment pull
on the lower segment causing it to stretch.
 This aided by the force applied by the
descending presenting part.

The Retraction Ring
 The ridge develop between the upper and
lower uterine segments, known as the
retraction ring.
 The physiological ring gradually rises as
the upper uterine segment contracts and
retracts and the lower uterine segment
thins out to accommodate the descending
fetus.
 Once the cervix is fully dilated and the
fetus can leave the uterus, the retraction

Cervical Effacement
 Effacement refers to the inclusion (taking up)
of the cervical canal into the lower uterine
segment.
 It take place from above downward, that is
the muscle fibres surrounding the internal os
are drawn upwards by the retracted upper
segment and the cervix merges into the
lower uterine segment.
 The cervical canal widens at the level of the
internal os, where the condition of the
external os remains unchanged.

Cervical Dilatation
 Dilatation of cervix is the process of
enlargement of the os uterine from a
tightly closed aperture to an opening
large enough to permit the passage of
the fetal head.
 Dilatation is measured in centimeters
and full dilatation at term equates to
about 10 cm.

Show
 As a result of the dilatation of the cervix,
the operculum, which formed the cervical
plug during pregnancy, is released.
 The woman may observe a bloodstained
mucoid discharge a few hours before, or
within a few hours after, labour starts.
 The blood comes from the ruptured
capillaries in the parietal decidua where the
chorion has become detached from the
dilating cervix an should only be staining.

Formation of Forewater
 As the lower uterine segment forms and
stretches, the chorion becomes detached
from it and the increased intrauterine
pressure causes its loosened part of the
sac of fluid to bulge downwards into the
internal os, to the depth of 6-12 mm.
 The well flexes head fits snugly into the
cervix and cuts off the fluid in front of the
head from that which surrounds the body,
forming 2 separate pools of fluid.
 The former is known as forewaters and the
latter the hindwaters.

General Fluid Pressure
 While the membranes remain intact,
the pressure of the uterine contractions
is exerted on the fluid and, as fluid is
not compressible, the pressure is
equalized throughout the uterus and
over the fetal body; it is known as
general fluid pressure.

Rupture of The Membrane
 The optimal physiological time for the
membranes to rupture spontaneously is
at the end of the first stage of labour
after the cervix becomes fully dilated
and no longer supports the bag of
forewaters.
 The uterine contractions are also
applying increasing expulsive force at
this time.

Fetal Axis Pressure
 During each contraction the uterus rises
forward and the force of the fundal
contraction is transmitted to the upper
pole of the fetus, down the long axis of
the fetus and applied by the presenting
part to the cervix.
 This is known as fetal axis pressure.

Early Labour Phase ( Latent Phase)
 Approximately 8-12 hours.
 Cervix will efface and dilate to 4 cm
 Contractions will last about 30-45
seconds, giving you 5-30 minutes of
rest between contractions .
 Contractions are typically mild and
somewhat irregular, but become
progressively stronger and more

 Contractions can feel like aching in
your lower back, menstrual cramps, and
pressure/tightening in the pelvic area .
 Amniotic sac rupture and can happen
any time within the first stage of labour.

Active Labor Phase
 Active labour will last about 3-5 hours.
 Cervix will dilate from 4cm to 10cm.
 Contractions will last about 45-60 seconds
with 3-5 minutes rest in between.
 Contractions will feel stronger and longer.
 This is usually the time to head to the hospital
or birth center.

PHYSIOLOGY OF SECOND
STAGE OF LABOUR

OBJECTIVES SECOND STAGE
OF LABOUR
 Define the second stage of labour.
 State the duration of second stage of
labour.
 Explain the physiological changes during
the second stage of labour.
 State the external signs of second stage
of
labour.

DEFINITION OF SECOND STAGE
LABOUR
 The part of labour from the full
dilatation of the cervix prior to or in
the
absent of involuntary expulsive and
end
when the fetus is completely out of
the
birth canal.
 The second stage of labour is also

Duration of second stage of
labour
 Primid = 1 hour
 Multipara = 30 min – 45 min

Uterine action
 Contraction become stronger and longer
but may be less frequent, allowing both
mother and fetus regular recovery periods.
 The membrane often rupture
spontaneously towards the end of the first
stage or during transition to the second
stage.

 The consequent drainage of liquor allow
the hard, round fetal head or the
buttocks to be directly applied to the
vaginal tissues. This pressure aids
distension.
Fetal axis pressure increases flexion of
the head, which results in smaller
presenting diameters, more rapid
progress and less trauma to both mother
and fetus.

 The contraction becomes expulsive as the
fetus descends further into the vagina.
 Pressure from the presenting part
stimulates nerve receptors in the pelvic floor
“this is termed the “ Ferguson reflex “and
the woman experiences the need to push.
 The mother’s response is to employ her
secondary powers of expulsion by
contacting her abdominal muscles and
diaphragm.

 Soft tissue displacement.
 As the hard fetal descends, the soft
tissues of the pelvis becomes
displaced.
 Anterior - Bladder
 Posterior- Rectum
 The levator ani muscles
 Perineal body.

 The fetal head becomes visibles at the
vulva, advansing each contraction and
receding between contractions until
crowning take place.
 The head is then born.
 The shoulders and body follow with next
contraction, accompanied by a gush of
amniotic fluid and sometimes of blood.
 The second stage culminate in the birth
of the baby.

Expulsive Uterine Contraction
 Feel a strong desire to push before full
dilatation occurs.
 Early urge to push will lead to
maternal exhaustion and or cervical
oedema or trauma.

Rupture of The Forewaters
 May occur any time during labour.

Anus Poulting
 Deep engagement of the presenting
part may produce this sign during the
latter part of the first stage.

Blood Stain
 Loss of bloodstained mucus which
often accompanies rapid dilatation of
the cervical os towards the end of the
first stage of labour.
• It must be distinguished from frank
fresh blood loss cause by partial
saperation of the placenta or a rupture
vasa praevia.

Learning objectives:
1) State the definition of third stage of
labour.
2) Describe the physiology changes of
third stages of labour.
3) State the method of placenta
separation.

Definition:
 The third stage can be defined as the
period from the birth of the baby to
complete expulsion of the placenta and
membranes with control blood loss.
 Duration usually last between 5 to 15
minutes but any period up to 1 hour is
considered to be within normal limits.

Physiological changes or the
third stage of labour

Separation and descent of placenta.
Mechanical Factors
 As the baby is born, the uterus
spontaneously contracts around its
diminishing contents.
 The uterine fundus now lies just below the
level of the umbilicus.
 Thus, by the beginning or third stage, the
placental site has already diminished in
area.

 As this occurs the placenta becomes
compressed and the blood in the intervillous
spaces is forced back into the spongy layer of
the decidua basalis.
 Retraction of the obligue uterine muscle fibres
exerts pressure on the blood vessels so that
blood does not drain back into maternal system.
 The vessels during this process becomes tense
and congested .With the next contraction the
distended veins burst and small amount of blood
seeps in between the thin septa of the spongy
layer and the placental surface, stripping it from
its attachment.

 As the surface area of the placental
attachment reduces, the relatively non
elastic placenta begins to detach from
the uterine wall.

Separation of fetal membranes
 The greates decrease in uterine cavity
surface area simultaneously throws the
fetal membranes – the amnion , chorion
and placenta decidua into innumerable
folds.
 Membranes usually remain insitu until
placental separation is nearly completed.
 These are then peeled off the uterine wall,
partly by traction that is exerted by
separated placenta, which lies in the lower
segment or upper vagina.

Haemostasis
 The normal volume of blood flow
through the placental site is 500 to
800ml/min.
 Reduce once the baby is born and the
placental site on the uterine wall was
diminished.

 The interplay of four factors within the
normal physiological processes that
control bleeding are:
1. Retraction of the oblique uterine
muscle fibres in the upper uterine
segment through which the tortuous
blood vessels intertwine
- the resultant thickening of the muscle
exert pressure on the torn vessels,
acting as clamps, and preventing
haemorrhage.

2. Vigorous uterine contraction following
separation
- this bring the wall into apposition so
that further pressure is exerted on the
placental site.
3. There is transitory activation of the
coagulation and fibrinolytic systems
during and immediately following
placental separation.

4. Breast feeding
- The release of oxytocin from the
posterior pituitary in response to skin
to skin contact between mother and
baby.
- The baby’s nuzzling at the breast
cause uterine contraction.

Schultze Method
 Separation usually begins centrally so
that retroplacental clot is formed.
 Increased weight helps to strip the
adherent lateral borders and peel the
membranes off the uterine wall so that
the clot thus formed becomes enclosed
in a membranous bag as placenta
descents, fetal surface first.

 This process of separation is
associated with more complete
shearing of both placenta and
membranes and less fluid blood loss.

Matthew’s Duncan Method
 The placenta may begin to detach unevenly at
one of its lateral borders.
 The blood escapes so that separation is
unaided by the formation of the retroplacental
clot.
 The placenta descends , slipping sideways ,
maternal surface firsts.
 This process take longer and is associated with
ragged, incomplete expulsion of the
membranes and higher fluid blood loss.

 Once separation has occured the
uterus contracts strongly, forcing
placenta and membranes to fall into
the vagina.

Saperation of Placenta
 Uterine contract and retract, uterus
becomes round and firm
 Gushing of blood
 Lengthen of the umbilical cord

Conclusion
The first stage commences with the onset of labour and
terminates when the cervix has reached full dilatation and
is no
longer palpable. The hormone factor like oestrogen,
progesterone, oxytocin , foetal cortisone relaxin will take
place
during onset of labour.
The second stage or stage of expulsion begins at full
cervical
dilatation and ends with expulsion of the fetus. The
hormone
factor will continues from the first stage of labour until the
fetus is come out.
The third stage or placental stage begins with the
delivery of
the child and ends with the expulsion of the placenta. This

Reference:
 Jayne Marshall. Maureen Sixteenth
Edition (2014) Myles Textbook For
Midwives
 William’s Obstetrics Twenty-Second
Ed. Cunningham, F. Gary, et al, Ch.
17.
 Penny, P.T, et al, Ch. 9. Pregnancy,
Childbirth and the Newborn: The
Complete Guide. Simkin,

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