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Labour, Stages and
its Physiology
Shrooti Shah
M.Sc.Nursing
Batch 2011
Contents
 Definitions
 Normal and abnormal labour
 Causes of onset of labour
 False labour pain and true labour pain
 Stages of labour
 Physiology of first stage of labour
 Physiology of second stage of labour
 Mechanism of normal labour
 Physiology of third stage of labour
Definition
 Series of events that takes place in the
genital organ in an effort to expel the viable
products of conception out of the womb
through the vagina into the outer world is
called labour.
 It may occur prior to 37 completed weeks,
when it is called preterm labour.
 Delivery is the expulsion or extraction of
viable fetus out of the womb.
Normal labour (Eutocia)
Labour is called normal if it fulfills the
following criteria:
 Spontaneous in onset and at term.
 With vertex presentation
 Without undue prolongation
 Natural termination with minimal aids
 Without having any complications affecting
the health of mother and/or baby.
Abnormal labour (Dystocia)
Any deviation from the definition of
normal labour is called abnormal
labour.
Date of onset of labour
 It is unpredictable to foretell precisely the
exact date of onset of labour.
 Calculation from Naegele‘s formula is only a
rough guide.
 Based on the formula, labour starts approx.
on the expected date in 4%, one week on
either side in 50%, 2 weeks earlier and 1
week later in 80%, at 42 weeks in 10% and at
43 weeks plus in 4%.
Causes of Onset of labour
1. Uterine distension
2. Feto-placental contribution
3. Oestrogen
4. Progesterone
5. Prostaglandins
6. Oxytocin
7. Neurological factors
Oestrogen
 Increase the release of oxytocin from maternal
pituitary.
 Promotes the synthesis of receptors for oxytocin in
the myometrium and decidua.
 Accelerates lysosomal disintegration in amnion cells
resulting in amnion cells resulting in increased
prostaglandin synthesis.
 Stimulates the synthesis of myometrial contractile
protein ---actinomyosin through cAMP.
 Increases the excitability of the myometrial cell
membranes.
Progesterone
 Increased fetal production of dehydroepiandrosterone
sulphate (DHEA-S) and cortisol inhibits the
conversion of fetal pregnenolone to progesterone.
Progesterone levels therefore fall before labour.
 It is the alteration in the oestrogen:progesterone ratio
rather than the fall in the absolute concentration of
progesterone which is linked with the prostaglandin
synthesis.
Prostaglandins
 Prostaglandins are the important factor which
initiate and maintain labour.
 The major sites of synthesis of prostaglandins are ---
amnion, chorion, decidual cells and myometrium.
 Synthesis is triggered by –rise in oestrogen level,
glucocorticoids, mechanical stretching in the late
pregnancy, increase in cytokines, infection, vaginal
examination, separation or rupture of membranes
Oxytocin
 Oxytocin receptors are increased in the uterus with
the onset of labour.
 Oxytocin promotes the release of prostaglandins from
the decidua.
 Oxytocin synthesis is increased in the decidua and in
the placenta.
 Vaginal examination and amniotomy cause rise in
maternal plasma oxytocin level (Ferguson reflex).
Neurological factor
 Both α and β adrenergic receptors are present in the
myometrium; oestrogen causing the α receptors and
progesterone the β receptoors to function
predominantly.
 The contractile response is initiated through the α
receptors of the post ganglionic nerve fibres in and
around the cervix and the lower part of the uterus.
False labour pain
Features
1. Dull in nature and usually confined to the
lower abdomen and groin.
2. Continuous and unrelated with hardening of
the uterus
3. Without any effect on dilatation of the cervix.
4. Usually relieved by medications.
Pre labour (premonitory stage)
Begins:
 Primigravida: 2 or 3 weeks before the onset
of true labour.
 Multigravida: few days prior.
Features of prelabour
 Lightening
 Cervical changes
 Appearance of false pain
True labour pain
Features of true labour pain:
 Painful uterine contractions (labour pain) at
regular intervals
 Contraction with increasing intensity and
duration
 Show
 Progressive effacement and dilatation of the
cervix
 Formation of the ―bag of waters‖.
Stages of labour
First stage of labour
Second stage of labour
Third stage of labour
Fourth stage of labour
First stage of labour
 This starts from the onset of true labour pain
and ends with full dilatation of cervix. It is in
other words, the ―cervical stage‖ of labour.
 Its average duration is 12 hours in
primigravida and 6 hours in multigravida.
 There are two phases of first stage of labour:
 Latent phase
 Active phase
Phases of first stage of labour
 The latent phase: is the time between the
onset of labour and 3- 4 cm dilatation and
cervix becomes fully effaced. It usually lasts
between 3 and 8 hours, being shorter in
multiparous women.
 The second phase: is the active stage and
describes the time between the end of latent
phase (3-4 cm dilatation) and full dilatation
(10cm). It is also variable in length, usually
lasting between 2 and 6 hours. Again it is
shorter in multiparous women.
During active phase
Cervical dilatation during the active
phase usually occurs at 1cm/hour or
more in a normal labour.
Second stage of labour
 It starts from the full dilation of the cervix and ends
with expulsion of fetus from the birth canal.
 It has got two phases
1. Propulsive phase-starts from full dilatation upto the
descent of the presenting part to the pelvic floor
2. Expulsive phase- is distinguished by maternal
bearing down efforts and ends with delivery of the
baby.
 Average duration is 2 hours in primigravida and 1
hour in multipara.
Third stage of labour
 The third stage begins after the expulsion of
fetus and ends with expulsion of placenta and
membranes; it also involves the control of
bleeding.
 A third stage lasting more than 30 minutes
should be considered abnormal.
Fourth stage of labour
 The fourth stage begins with the delivery of
the placenta and ends two hours later.
Physiology of first stage of labour
Uterine action
Fundal dominance:
 Each uterine contraction starts in the fundus
near one of the cornua and spreads across
and downwards.
 The contraction lasts longest in the fundus
where it is also most intense, but the peak is
reached simultaneously over the whole uterus
and the contraction fades from all parts
together.
Polarity
 Polarity is the term used to describe the
neuromuscular harmony that prevails
between the two poles or segments 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
contracts slightly and dilates to allow
expulsion to take place. If polarity is
disorganized then the progress of labour is
inhibited.
Contraction and retraction
Formation of upper and lower uterine
segments
 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 8-10 cm
in length. The lower segment is prepared for
distention and dilatation.
 The muscle content reduces from the fundus
to the cervix, where it is thinner.
Formation of upper and lower uterine
segments cont…
 When the labour begins, the retracted
longitudinal fibres in the upper segment pull
on the lower segment causing it to stretch;
this is aided by the descending presenting
part.
The Retraction ring
 The ridge forms between the upper and lower
uterine segments; this is 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 ring rises no
further.
Cervical effacement
 Effacement refers to the inclusion of the
cervical canal into the lower uterine segment.
 It takes 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 effacement cont…
Cervical dilatation
 Dilatation of cervix is the process of
enlargement of the os uteri 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.
Cervical dilatation
Show
 As a result of the dilatation of the cervix, the
operculum, which formed the cervical plug
during pregnancy, is lost. The woman may
see a blood stained 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.
Formation of fore water
 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.
 The former is known as ‗forewaters‘ and the
latter the ‗hindwaters‘.
Formation of forewater
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
the fetal body; it is known
as ‗general fluid pressure‘.
Rupture of 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.
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.
Physiology of second stage
of labour
Uterine action
 Contractions 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 allows the hard,
round fetal head 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.
Uterine action continued
 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 contracting
her abdominal muscles and diaphragm.
Soft tissue displacement
 As the hard fetal head descends, the soft
tissues of the pelvis becomes displaced.
 Anteriorly-Bladder
 Posteriorly- Rectum
 The levator ani muscles
 Perineal body
Soft tissue displacement cont…
 The fetal head becomes visible at the vulva,
advancing each contraction and receding
between contractions until crowning takes
place.
 The head is then born.
 The shoulders and body follow with next
contraction, accompanied by gush of amniotic
fluid and sometimes of blood.
 The second stage culminates in the birth of
the baby.
Presumptive signs of second stage of
labour
 Expulsive uterine contraction
 Rupture of forewaters
 Dilatation and gaping of the anus
 Appearance of the rhomboid of Michaelas
 Show
 Appearance of presenting part
Mechanism of normal
labour
Landmarks of pelvis
Diameter of Pelvis
Fetal skull
Lie
 It refers to the relationship of the long axis of
the fetus to the long axis of the centralized
uterus or maternal spine.
Presentation
Presenting part
 Is defined as the part of the presentation which
overlies the internal os and is felt by the
examining finger through the cervical opening.
Attitude
 The relation of the different parts of the fetus
to one another is called attitude of the fetus.
The universal attitude is that of flexion.
Denominator
 It is an arbitrary bony fixed point on the
presenting part which comes in relation with
the various quadrants of the maternal pelvis.
 The following are denominators of the
different presentations- occiput in vertex,
mentum in face, frontal eminence in brow,
sacrum in breech and acromion in shoulder
Position
Mechanism of labour
 As the fetus descends, soft tissue and bony
structures exert pressures which lead to
descent through the birth canal by a series of
movements. Collectively, these movements
are called the mechanism of labour.
Principles common to all mechanism
 Descent takes place
 Whichever part leads and first meets the
resistance of the pelvic floor will rotate
forwards until it comes under the symphysis
pubis.
 Whatever emerges from the pelvis will pivot
around the pubic bone.
Six considerations for normal labour
 The lie is longitudinal
 The presentation is cephalic
 The position is right or left occipitoanterior
 The attitude is one of the good flexion
 The denominator is the occiput
 The presenting part is the posterior part of the
anterior parietal bone.
Cardinal movement
 Engagement
 Descent
 Flexion
 Internal rotation of the head
 Extension of the head
 External Rotation/Restitution
 Internal rotation of the shoulders
 Lateral flexion
Engagement
 The mechanism by which the biparietal
diameter—the greatest transverse diameter in
an occiput presentation—passes through the
pelvic inlet is designated engagement.
Descent
 This movement is the first requisite for birth of the
newborn.
 Different in nulliparous and multigravid women.
 Throughout the first stage of labour the contraction
and retraction of the uterine muscles allow less
room in the uterus, exerting pressure on the fetus
to descend.
 Following rupture of the forewaters and the
exertion of maternal effort, progress speed up.
Flexion
 As soon as the descending head meets
resistance, whether from the cervix, walls of
the pelvis, or pelvic floor, then flexion of the
head normally results.
 Suboccipitobregmatic diameter (9.5 cm) is
substituted for the longer occipitofrontal
diameter (10 cm). The occiput becomes the
leading part.
Internal rotation of the head
 During contraction, the leading part is pushed
downwards onto the pelvic floor. The resistance of
this muscular diaphragm brings about rotation.
 Occiput gradually moves toward the symphysis pubis
anteriorly.
 Whichever part of the fetus meets the lateral half of
this slope will be directed forwards and towards the
center in a well flexed vertex presentation the occiput
leads, and rotates anteriorly through 1/8th of a circle
when it meets the pelvic floor. This causes a slight
twist in the neck as the head is no longer in direct
alignment with the shoulders.
Internal rotation cont…
 The anteroposterior diameter of the head now
lies in the widest (anteroposterior) diameter of
the pelvic outlet.
 The occiput slips beneath the sub-pubic arch
and crowning occurs when the head no
longer recedes between contraction and the
widest transverse diameter is born.
 Of flexion is maintained, the suboccipito
bregmatic diameter, usually distends the
vaginal orifice.
Extension of the head
 Once crowning has occurred the fetal head
can extend, pivoting on the suboccipital
region around the pubic bone.
 This releases the sinciput, face and chin,
which sweep the perineum and are born by a
movement of extension.
Restitution
 The twist in the neck of the fetus that resulted
from internal rotation is now corrected by a
slight untwisting movement.
 The occiput moves one-eight of a circle
towards the side from which it started
Internal rotation of the shoulders
 The shoulders undergo a similar rotation to
that of the head to lie in the widest diameter
of the pelvic outlet, namely anteroposterior.
 The anterior shoulder is first to reach the
levator ani muscle and is therefore rotates
anteriorly to lie under the symhysis pubis.
 It occurs in the same direction as restitution,
and the occiput of the fetal head now lies
laterally.
Lateral flexion
 Almost immediately after external rotation, the
anterior shoulder slips beneath the subpubic
arch and the posterior shoulder passes over
the perineum.
 After delivery of the shoulders, the rest of the
body is born by lateral flexion as the spine
bends sideways through the curved birth
canal.
v
v
Second stage ends with delivery of
baby.
Physiology of third stage of
labour
Physiology of third stage of
labour
Third stage of labour
 This stage begins immediately after delivery
of the fetus and involves the separation and
expulsion of the placenta and membranes,
involving the separation, descent and
expulsion of placenta and membranes and
control of hemorrhage from the placenta site.
 The third stage usually lasts between 5 and
15 minutes, but any period upto 30 minutes is
considered to be within normal limits.
Mechanical factors
 As the neonate 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 of the third stage, the
placental site has already diminished in area by
about 75%.
 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.
Mechanical factors
 Retraction of the oblique uterine muscle fibres exerts
pressure on the blood vessels so that blood does not
drain back into the maternal system.
 The vessels during this process become 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.
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
the placenta descends, fetal surface first.
 This process of separation is associated with
more shearing of both placenta and
membranes and less fluid blood loss.
Matthews Duncan method
 The placenta may begin to separate unevenly at
one of its lateral borders.
 The blood escapes so that separation is unaided
by the formation of a retroplacental clot.
 The placenta descends, slipping sideways,
maternal surface first.
 This process takes longer and is associated with
ragged, incomplete expulsion of the membranes
and a higher fluid blood loss.
Separation of fetal membranes
 The great decrease in uterine cavity surface area
simultaneously throws the fetal membranes—the
amnion, chorion and the parietal decidua—into
innumerable folds.
 Membranes usually remain in situ until placental
separation is nearly completed.
 These are then peeled off the uterine wall, partly
by further contraction of the myometrium and
partly by traction that is exerted by the separated
placenta, which lies in the lower segment or
upper vagina.
Homeostasis
 Retraction of the oblique uterine muscle fibres in
the upper uterine segment through which the
tortuous blood vessels interwine- the resultant
thickening of the muscles exert pressure on the
torn vessels, acting as clamps, so securing a
ligature action.
Homeostasis cont…
 Vigorous uterine contraction following
separation-this brings the walls into
apposition so that further pressure is exerted
on the placental site.
 There is transitory activation of the
coagulation and fibrinolytic systems during,
and immediately following placental
separation
Labour and its stages

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Labour and its stages

  • 1. Labour, Stages and its Physiology Shrooti Shah M.Sc.Nursing Batch 2011
  • 2. Contents  Definitions  Normal and abnormal labour  Causes of onset of labour  False labour pain and true labour pain  Stages of labour  Physiology of first stage of labour  Physiology of second stage of labour  Mechanism of normal labour  Physiology of third stage of labour
  • 3. Definition  Series of events that takes place in the genital organ in an effort to expel the viable products of conception out of the womb through the vagina into the outer world is called labour.  It may occur prior to 37 completed weeks, when it is called preterm labour.  Delivery is the expulsion or extraction of viable fetus out of the womb.
  • 4. Normal labour (Eutocia) Labour is called normal if it fulfills the following criteria:  Spontaneous in onset and at term.  With vertex presentation  Without undue prolongation  Natural termination with minimal aids  Without having any complications affecting the health of mother and/or baby.
  • 5. Abnormal labour (Dystocia) Any deviation from the definition of normal labour is called abnormal labour.
  • 6. Date of onset of labour  It is unpredictable to foretell precisely the exact date of onset of labour.  Calculation from Naegele‘s formula is only a rough guide.  Based on the formula, labour starts approx. on the expected date in 4%, one week on either side in 50%, 2 weeks earlier and 1 week later in 80%, at 42 weeks in 10% and at 43 weeks plus in 4%.
  • 7. Causes of Onset of labour 1. Uterine distension 2. Feto-placental contribution 3. Oestrogen 4. Progesterone 5. Prostaglandins 6. Oxytocin 7. Neurological factors
  • 8.
  • 9. Oestrogen  Increase the release of oxytocin from maternal pituitary.  Promotes the synthesis of receptors for oxytocin in the myometrium and decidua.  Accelerates lysosomal disintegration in amnion cells resulting in amnion cells resulting in increased prostaglandin synthesis.  Stimulates the synthesis of myometrial contractile protein ---actinomyosin through cAMP.  Increases the excitability of the myometrial cell membranes.
  • 10. Progesterone  Increased fetal production of dehydroepiandrosterone sulphate (DHEA-S) and cortisol inhibits the conversion of fetal pregnenolone to progesterone. Progesterone levels therefore fall before labour.  It is the alteration in the oestrogen:progesterone ratio rather than the fall in the absolute concentration of progesterone which is linked with the prostaglandin synthesis.
  • 11. Prostaglandins  Prostaglandins are the important factor which initiate and maintain labour.  The major sites of synthesis of prostaglandins are --- amnion, chorion, decidual cells and myometrium.  Synthesis is triggered by –rise in oestrogen level, glucocorticoids, mechanical stretching in the late pregnancy, increase in cytokines, infection, vaginal examination, separation or rupture of membranes
  • 12. Oxytocin  Oxytocin receptors are increased in the uterus with the onset of labour.  Oxytocin promotes the release of prostaglandins from the decidua.  Oxytocin synthesis is increased in the decidua and in the placenta.  Vaginal examination and amniotomy cause rise in maternal plasma oxytocin level (Ferguson reflex).
  • 13. Neurological factor  Both α and β adrenergic receptors are present in the myometrium; oestrogen causing the α receptors and progesterone the β receptoors to function predominantly.  The contractile response is initiated through the α receptors of the post ganglionic nerve fibres in and around the cervix and the lower part of the uterus.
  • 14. False labour pain Features 1. Dull in nature and usually confined to the lower abdomen and groin. 2. Continuous and unrelated with hardening of the uterus 3. Without any effect on dilatation of the cervix. 4. Usually relieved by medications.
  • 15. Pre labour (premonitory stage) Begins:  Primigravida: 2 or 3 weeks before the onset of true labour.  Multigravida: few days prior.
  • 16. Features of prelabour  Lightening  Cervical changes  Appearance of false pain
  • 17. True labour pain Features of true labour pain:  Painful uterine contractions (labour pain) at regular intervals  Contraction with increasing intensity and duration  Show  Progressive effacement and dilatation of the cervix  Formation of the ―bag of waters‖.
  • 18. Stages of labour First stage of labour Second stage of labour Third stage of labour Fourth stage of labour
  • 19. First stage of labour  This starts from the onset of true labour pain and ends with full dilatation of cervix. It is in other words, the ―cervical stage‖ of labour.  Its average duration is 12 hours in primigravida and 6 hours in multigravida.  There are two phases of first stage of labour:  Latent phase  Active phase
  • 20. Phases of first stage of labour  The latent phase: is the time between the onset of labour and 3- 4 cm dilatation and cervix becomes fully effaced. It usually lasts between 3 and 8 hours, being shorter in multiparous women.  The second phase: is the active stage and describes the time between the end of latent phase (3-4 cm dilatation) and full dilatation (10cm). It is also variable in length, usually lasting between 2 and 6 hours. Again it is shorter in multiparous women.
  • 21. During active phase Cervical dilatation during the active phase usually occurs at 1cm/hour or more in a normal labour.
  • 22. Second stage of labour  It starts from the full dilation of the cervix and ends with expulsion of fetus from the birth canal.  It has got two phases 1. Propulsive phase-starts from full dilatation upto the descent of the presenting part to the pelvic floor 2. Expulsive phase- is distinguished by maternal bearing down efforts and ends with delivery of the baby.  Average duration is 2 hours in primigravida and 1 hour in multipara.
  • 23. Third stage of labour  The third stage begins after the expulsion of fetus and ends with expulsion of placenta and membranes; it also involves the control of bleeding.  A third stage lasting more than 30 minutes should be considered abnormal.
  • 24. Fourth stage of labour  The fourth stage begins with the delivery of the placenta and ends two hours later.
  • 25. Physiology of first stage of labour Uterine action Fundal dominance:  Each uterine contraction starts in the fundus near one of the cornua and spreads across and downwards.  The contraction lasts longest in the fundus where it is also most intense, but the peak is reached simultaneously over the whole uterus and the contraction fades from all parts together.
  • 26. Polarity  Polarity is the term used to describe the neuromuscular harmony that prevails between the two poles or segments 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 contracts slightly and dilates to allow expulsion to take place. If polarity is disorganized then the progress of labour is inhibited.
  • 28. Formation of upper and lower uterine segments  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 8-10 cm in length. The lower segment is prepared for distention and dilatation.  The muscle content reduces from the fundus to the cervix, where it is thinner.
  • 29. Formation of upper and lower uterine segments cont…  When the labour begins, the retracted longitudinal fibres in the upper segment pull on the lower segment causing it to stretch; this is aided by the descending presenting part.
  • 30. The Retraction ring  The ridge forms between the upper and lower uterine segments; this is 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 ring rises no further.
  • 31. Cervical effacement  Effacement refers to the inclusion of the cervical canal into the lower uterine segment.  It takes 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.
  • 33. Cervical dilatation  Dilatation of cervix is the process of enlargement of the os uteri 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.
  • 35. Show  As a result of the dilatation of the cervix, the operculum, which formed the cervical plug during pregnancy, is lost. The woman may see a blood stained 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.
  • 36. Formation of fore water  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.  The former is known as ‗forewaters‘ and the latter the ‗hindwaters‘.
  • 38. 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 the fetal body; it is known as ‗general fluid pressure‘.
  • 39. Rupture of 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.
  • 40. 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.
  • 41. Physiology of second stage of labour
  • 42. Uterine action  Contractions 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 allows the hard, round fetal head 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.
  • 43. Uterine action continued  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 contracting her abdominal muscles and diaphragm.
  • 44. Soft tissue displacement  As the hard fetal head descends, the soft tissues of the pelvis becomes displaced.  Anteriorly-Bladder  Posteriorly- Rectum  The levator ani muscles  Perineal body
  • 45. Soft tissue displacement cont…  The fetal head becomes visible at the vulva, advancing each contraction and receding between contractions until crowning takes place.  The head is then born.  The shoulders and body follow with next contraction, accompanied by gush of amniotic fluid and sometimes of blood.  The second stage culminates in the birth of the baby.
  • 46. Presumptive signs of second stage of labour  Expulsive uterine contraction  Rupture of forewaters  Dilatation and gaping of the anus  Appearance of the rhomboid of Michaelas  Show  Appearance of presenting part
  • 51. Lie  It refers to the relationship of the long axis of the fetus to the long axis of the centralized uterus or maternal spine.
  • 53. Presenting part  Is defined as the part of the presentation which overlies the internal os and is felt by the examining finger through the cervical opening.
  • 54. Attitude  The relation of the different parts of the fetus to one another is called attitude of the fetus. The universal attitude is that of flexion.
  • 55. Denominator  It is an arbitrary bony fixed point on the presenting part which comes in relation with the various quadrants of the maternal pelvis.  The following are denominators of the different presentations- occiput in vertex, mentum in face, frontal eminence in brow, sacrum in breech and acromion in shoulder
  • 57. Mechanism of labour  As the fetus descends, soft tissue and bony structures exert pressures which lead to descent through the birth canal by a series of movements. Collectively, these movements are called the mechanism of labour.
  • 58. Principles common to all mechanism  Descent takes place  Whichever part leads and first meets the resistance of the pelvic floor will rotate forwards until it comes under the symphysis pubis.  Whatever emerges from the pelvis will pivot around the pubic bone.
  • 59. Six considerations for normal labour  The lie is longitudinal  The presentation is cephalic  The position is right or left occipitoanterior  The attitude is one of the good flexion  The denominator is the occiput  The presenting part is the posterior part of the anterior parietal bone.
  • 60. Cardinal movement  Engagement  Descent  Flexion  Internal rotation of the head  Extension of the head  External Rotation/Restitution  Internal rotation of the shoulders  Lateral flexion
  • 61.
  • 62. Engagement  The mechanism by which the biparietal diameter—the greatest transverse diameter in an occiput presentation—passes through the pelvic inlet is designated engagement.
  • 63. Descent  This movement is the first requisite for birth of the newborn.  Different in nulliparous and multigravid women.  Throughout the first stage of labour the contraction and retraction of the uterine muscles allow less room in the uterus, exerting pressure on the fetus to descend.  Following rupture of the forewaters and the exertion of maternal effort, progress speed up.
  • 64.
  • 65. Flexion  As soon as the descending head meets resistance, whether from the cervix, walls of the pelvis, or pelvic floor, then flexion of the head normally results.  Suboccipitobregmatic diameter (9.5 cm) is substituted for the longer occipitofrontal diameter (10 cm). The occiput becomes the leading part.
  • 66. Internal rotation of the head  During contraction, the leading part is pushed downwards onto the pelvic floor. The resistance of this muscular diaphragm brings about rotation.  Occiput gradually moves toward the symphysis pubis anteriorly.  Whichever part of the fetus meets the lateral half of this slope will be directed forwards and towards the center in a well flexed vertex presentation the occiput leads, and rotates anteriorly through 1/8th of a circle when it meets the pelvic floor. This causes a slight twist in the neck as the head is no longer in direct alignment with the shoulders.
  • 67. Internal rotation cont…  The anteroposterior diameter of the head now lies in the widest (anteroposterior) diameter of the pelvic outlet.  The occiput slips beneath the sub-pubic arch and crowning occurs when the head no longer recedes between contraction and the widest transverse diameter is born.  Of flexion is maintained, the suboccipito bregmatic diameter, usually distends the vaginal orifice.
  • 68.
  • 69.
  • 70. Extension of the head  Once crowning has occurred the fetal head can extend, pivoting on the suboccipital region around the pubic bone.  This releases the sinciput, face and chin, which sweep the perineum and are born by a movement of extension.
  • 71.
  • 72. Restitution  The twist in the neck of the fetus that resulted from internal rotation is now corrected by a slight untwisting movement.  The occiput moves one-eight of a circle towards the side from which it started
  • 73.
  • 74. Internal rotation of the shoulders  The shoulders undergo a similar rotation to that of the head to lie in the widest diameter of the pelvic outlet, namely anteroposterior.  The anterior shoulder is first to reach the levator ani muscle and is therefore rotates anteriorly to lie under the symhysis pubis.  It occurs in the same direction as restitution, and the occiput of the fetal head now lies laterally.
  • 75. Lateral flexion  Almost immediately after external rotation, the anterior shoulder slips beneath the subpubic arch and the posterior shoulder passes over the perineum.  After delivery of the shoulders, the rest of the body is born by lateral flexion as the spine bends sideways through the curved birth canal.
  • 76. v
  • 77. v
  • 78. Second stage ends with delivery of baby.
  • 79. Physiology of third stage of labour
  • 80. Physiology of third stage of labour
  • 81. Third stage of labour  This stage begins immediately after delivery of the fetus and involves the separation and expulsion of the placenta and membranes, involving the separation, descent and expulsion of placenta and membranes and control of hemorrhage from the placenta site.  The third stage usually lasts between 5 and 15 minutes, but any period upto 30 minutes is considered to be within normal limits.
  • 82. Mechanical factors  As the neonate 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 of the third stage, the placental site has already diminished in area by about 75%.  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.
  • 83.
  • 84. Mechanical factors  Retraction of the oblique uterine muscle fibres exerts pressure on the blood vessels so that blood does not drain back into the maternal system.  The vessels during this process become 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.
  • 85. 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 the placenta descends, fetal surface first.  This process of separation is associated with more shearing of both placenta and membranes and less fluid blood loss.
  • 86. Matthews Duncan method  The placenta may begin to separate unevenly at one of its lateral borders.  The blood escapes so that separation is unaided by the formation of a retroplacental clot.  The placenta descends, slipping sideways, maternal surface first.  This process takes longer and is associated with ragged, incomplete expulsion of the membranes and a higher fluid blood loss.
  • 87.
  • 88. Separation of fetal membranes  The great decrease in uterine cavity surface area simultaneously throws the fetal membranes—the amnion, chorion and the parietal decidua—into innumerable folds.  Membranes usually remain in situ until placental separation is nearly completed.  These are then peeled off the uterine wall, partly by further contraction of the myometrium and partly by traction that is exerted by the separated placenta, which lies in the lower segment or upper vagina.
  • 89. Homeostasis  Retraction of the oblique uterine muscle fibres in the upper uterine segment through which the tortuous blood vessels interwine- the resultant thickening of the muscles exert pressure on the torn vessels, acting as clamps, so securing a ligature action.
  • 90. Homeostasis cont…  Vigorous uterine contraction following separation-this brings the walls into apposition so that further pressure is exerted on the placental site.  There is transitory activation of the coagulation and fibrinolytic systems during, and immediately following placental separation