Lecture 5
PHASES OF PARTURITION
STAGES OF LABOR
MECHANISM OF NORMAL LABOR IN
OCCIPUT PRESENTATION
Prof. Vlad TICA, MD, PhD
PHASES OF PARTURITION
 Labor : uterine contractions that effect dilatation of
cervix and force fetus through birth canal
 Parturition: bringing forth of young, encompass all
physiological processes involved in birthing
 Phase 0: Prelude to Parturition
 Phase 1: Preparation for Labor
 Phase 2: Process of Labor
 Phase 3: Parturition Recovery
PHASES OF PARTURITION &
ONSET OF LABOR
 Divide 4 uterine phases: correspond to major
physiological transient of myometrium and cervix
during pregnancy
PHASE 0: UT QUIESCENCE
 Uterine smooth m tranquility with maintenance of
cervical structural integrity
 Unresponsive to natural stimuli, contractile paralysis
 Myometrium : quiescent state
 Cervix : firm unyielding
 Successful anatomical structural integrity :essential for
successful parturition
 Some myometrial contraction occur not cause cervix
dilation  Braxton-Hicks contraction / false labor
PHASE 0: UT QUIESCENCE
 Braxton – Hicks contraction or false labor
•
myometrial contractions that do not cause
cervical dilatation
•
unpredictability in occurrence
•
lack of intensity
•
brevity of duration
•
discomfort – confined to low abdomen & groin
PHASE 1: PREPARATION FOR LABOR
 Uterine awakening or activation
 Progression of change in uterus during last 6-8 weeks
of pregnancy
 Cervical change
 Myometrial change
PHASE 1: PREPARATION FOR LABOR
CERVICAL CHANGE
 Initiation of parturition: Cx soften, yield, more readily
dilatable
 Fundus transformed to produce effective contraction
that drive fetus through Cx & birth canal
 Failure of coordinated interaction  unfavorable preg
outcome
PHASE 1: PREPARATION FOR LABOR
CERVICAL CHANGE

Change of state of bundles of collagen fiber



Collagen breakdown & rearrangement of collagen fiber
bundles (number & size)
Chages in relative amount of glycosaminoglycans
(hyaluronic acid, capacity of Cx to retain water)

Dermatan sulfate (need for collagen fiber cross linking)

Production of cytokine  degrade collgen
Cx thinning, softening relaxation Cx initiate
diatation
PHASE 1: PREPARATION FOR LABOR
CERVICAL CHANGE
 PG E2 & F2a : modification of collagen & alteration in
relative amount of glycosaminoglycans
 Cx softening or ripenning to facilitate induction of
labor
PHASE 1: PREPARATION FOR LABOR
MYOMETRIAL CHANGE
 Increase Ut irritability & responsiveness to uterotonins
 Alterations in expression of key enzyme CAP
(contraction-associated proteins) - control myometrium
contractility
 Myometrial oxytocin R
 Myometrial cell gap junction protein (ex connexin -43)
 Formation lower Ut segment
PHASE 2 : PROCESS OF LABOR
 Active labor : Ut contrations bring about progressive
cervical dilatation & delivery
 3 stage of labor
PHASE 2: PROCESS OF LABOR
1st STAGE OF LABOR
 begins when uterine contraction of sufficient
frequency, intensity & duration
 ends when Cx is fully dilatated (10cm)
 stage of cervical effacement & dilatation
2nd STAGE OF LABOR
 begins when complete dilatation of Cx
 ends with delivery of fetus
 stage of expulsion of fetus
PHASE 2: PROCESS OF LABOR
3rd STAGE OF LABOR
 begins after delivery of fetus
 ends with delivery of placenta and fetal membranes
 stage of separation & expulsion of placenta
4th STAGE OF LABOR
 begins after placenta and fetal membranes
 ends after 2 hours
 stage of immediate puerperium
PHASE 2: PROCESS OF LABOR
PHASE 2: PROCESS OF LABOR
st
1
STAGE OF LABOR:
CLINICAL ONSET OF LABOR
 Formation of distinct lower & upper Ut segment:
•
2 distinct parts (anatomically & physiologically)
1. UPPER SEGMENT
 actively contracting
 becomes thicker as labor advances
 quite firm or hard
2. LOWER SEGMENT
 relatively passive
 develops into a much thinly walled passage for the fetus
 much less firm
SEQUENCE OF DEVELOPMENT OF
SEGMENT & RING IN UTERUS
IN PREGNANT WOMEN AT TERM & IN LABOR
Cx near end of pregnacy
before labor
Beginning effacement of
Cx
Further effacement of
Cx
Cervical canal obliterated
CERVICAL CHANGE INDUCED DURING
1st STAGE OF LABOR
CERVICAL CHANGE INDUCED DURING
st
1 STAGE OF LABOR
2 phases of cervical dilatation:
1. LATENT PHASE
• more variable
• subject to sensitive changes by extraneous factors &
by sedation (prolongation) & myometrial stimulation
(shortening)
2. ACTIVE PHASE
• acceleration phase - usually predictive of outcome
• phase of maximum slope
• deceleration phase
2nd STAGE OF LABOR:
FETAL DESCENT
•
In many nulliparas
•
engagement accomplished before labor begins
•
further descent not occur until late in labor
• increased rates of descent are ordinarily observed
during the phase of maximum slope
2nd STAGE OF LABOR: FETAL DESCENT
nd
2
STAGE OF LABOR:
FETAL DESCENT
Labor course divided fuctionally on basis of expected
evolution of dilatation & descent curves into 3 divisions:
PREPARATORY DIVISION
- latent & acceleration phases
DILATATIONAL DIVISION
- phase of maximum slope of cervical dilatation
- most rapid rate of dilatation occur
PELVIC DIVISION
- deceleration phase & second stage while concurrent
with phase of maximum slope of fetal descent
rd
3
STAGE OF LABOR:
DELIVERY OF PLACENTA & MEMBRANES
th
4
STAGE OF LABOR:
IMMEDIATE PUERPERIUM
PHASE 3 OF PARTURITION:
PROCESS OF LABOR
 Immediately after delivery & for 2 hours or so
thereafter, myometrium in state of rigid & persistent
contraction & retraction
 effect compression of large Ut vessels
 Severe PPH prevented
 Involution of Ut & reinstitution of ovulation
 Complete Ut involution : 4~6 wks
 Infertility persist as long as breast feeding is continued
( lactation  anovulation & amenorrhea)
LIE, PRESENTATION, ATTITUDE &
POSITION
FETAL LIE
 The relation of the long axis of the fetus to that of the
mother
 Longitudinal lie - found in 99% of labours at term
 Transverse lie - multiparity, placenta praevia, hydramnios,
uterine anomalies
 Oblique lie: unstable (become logitudinal or transversal)
 By abdominal palpation, vaginal examination, and
auscultation, or by technical means (USG, X-ray)
LIE, PRESENTATION, ATTITUDE &
POSITION
FETAL PRESENTATION
 The presenting part is the portion of the body of the fetus
that is foremost in the birth canal
 The presenting part can be felt through the cervix on
vaginal examination
 Longitudinal lie  cephalic presentation
 breech presentation
 Transverse lie  shoulder presentation
LIE, PRESENTATION, ATTITUDE &
POSITION
CEPHALIC PRESENTATION
 Head is flexed sharply  vertex / occiput presentation
 Head is extended sharply  face presentation
 Partially flexed  bregma presenting (sinciput
presentation)
 Partially extended  brow presentation
LIE, PRESENTATION, ATTITUDE &
POSITION
BREECH PRESENTATION
 Frank breech
 Complete breech
 Footling breech
LIE, PRESENTATION, ATTITUDE &
POSITION
ATTITUDE
 Posture of the fetus  folded on itself to accommodate the
shape of the uterus
 Flexed head, thighs, knees &feet
 The arms crossed over the chest
 Face presentation  extended concave contour of the
vertebral column
.
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A
B
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c
D
(A) vertex
(B) sinciput
(C) brow
(D) face
Longitudinal lie. Cephalic presentation. Differences in attitude of fetal
body,
Note changes in fetal attitude in relation to fetal vertex as the fetal head
becomes less flexed
I
I
Longitudinal lie. Frank breech
presentation.
Longitudinal lie. Complete breech
presentation.
Longitudinal lie. Incomplete, or footling, breech presentation
POSITION
The relation of an arbitrary chosen point of the fetal
presenting part to the Rt or Lt side of the maternal birth
canal
The chosen point:
 Vertex presentation  occiput
 Face presentation  mentum
 Breech presentation  sacrum
Each presentation has 2 positions: Rt or Lt
Each position has 3 varieties : anterior, transverse,
posterior
OA
ROA
LOA
ROT
LOT
LOP
ROP
OP
LONGITUDINAL LIE VERTEX PRESENTATION
LOA
~
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LOP
Right occiput posterior (ROP)
Right occiput transverse (ROT)
s
A
Longitudinal lie. Vertex presentation
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Right occiput anterior (ROA)
FREQUENCY OF VARIOUS
PRESENTATIONS & POSITIONS
AT TERM
 Vertex  96%
2/3 Lt
1/3 Rt
 Breech  3.5%
 Face 0.3%
 Shoulder 0.4%
Left mento-anterior
Right mento-anterior
Right mento-posterior
Longitudinal lie. Face presentation.
Left and right anterior and posterior positions.
~
Longitudinal lie. Breech presentation LSP
Transverse lie. Right acromio-dorso-posterior position (RADP). The
shoulder of the fetus is to the mother's right, and the back is posterior
MECHANISM OF LABOUR WITH
OCCIPUT PRESENTATIONS
THE CARDINAL MOVEMENTS OF
LABOUR
1 - ENGAGEMENT
The greatest transverse diameter BPD passes through the pelvic
inlet
It may occur in the last few weeks of pregnancy or only in labour
especially in multipara
The fetus enters the pelvis in transverse or oblique diameter
 LOT  40%
 ROT  20%
 OP  20% ROP > LOP
 ROA / LOA  20%
THE CARDINAL MOVEMENTS OF
LABOUR
 Asynclitism
The sagittal sutures of the head deflects ant towards the
symphysis pubis or post towards the sacrum
2 - DESCENT
 In nullipara engagement takes place before the onset of
labour & further descent may not occur till the 2nd stage
 In multipara descent begins with engagement
 It is gradually progressive till the fetus is delivered
 It is affected by the uterine contractions & thinning of the
lower segment
Anterior asynclitism
Naegele's obliquity
Normal synclitism
Posterior asynclitism
Litzmann's obliquity
Ear presentation
3-FLEXION
 The descending head meets resistance of pelvic floor, Cx
& walls of the pelvis  flexion
 The shorter suboccipito-begmatic is substituted for the
longer occipito-frontal
Lever action producing flexion of the head; conversion from
occipito-frontal to suboccipito-bregmatic diameter typically reduces
the anteroposterior diameter from nearly 12 to 9.5 cm
4 degrees of head flexion
A
c
Indicated by the solid line the
occipitomental diameter; the
broken line connects the center
of the anterior fontanel with
posterior fontanel:
A. Flexion poor
B. Flexion moderate
C. Flexion advanced
D. Flexion complete
Note that with flexion complete
the chin is on the chest, and the
suboccipitobregmatic diameter,
the shortest anteroposterior
A diameter of the fetal head, is
c
passing through the pelvic inlet
D
4-INTERNAL ROTATION
 Turning of the head from the OT position  anteriorly
towards the symphysis pubis ie. Occiput moves from
transverse to anterior 45º
 Less commonly OT  posteriorly towards the sacrum
135º
 It is not accomplished till the head has reached the
spines
The levator ani muscles form a V shaped sling that tend
to rotate the vertex anteriorly
 It is completed by the time the head reaches the pelvic
floor 2/3 or shortly after ¼
EXTENSION
 When the flexed head reaches the vulva it undergoes
extension  the base of the occiput will be in direct
contact with the inferior margin of the symphysis pubis
 Crowning  the largest diameter of the fetal head is
encircled by the vulvar ring
 The head is born by further extension as the occiput,
bregma, forehead, nose, mouth & chin pass successively
over the perineum
EXTERNAL ROTATION RESTITUTION
 After delivery of the head it returns to the position it
occupied at engagement, the natural position relative to
the shoulders (oblique position)
 Then the fetal body will rotate to bring one shoulder
anterior behind the symphysis pubis (biacromial
diameter into the APD of the pelvic outlet)
 Restitution is followed by complete external rotation to
transverse position (occiput lies to next to left maternal
thigh)
 The anterior shoulder slips under the pubis
 By lateral flexion of the fetal body the post shoulder will
be delivered & the rest of the body will follow
3
0
2
2.Engagement;descent, flexion
6. Restitution (external rotation)
3. Further descent, internal rotation
4. Complete rotation, beginning extension
Cardinal movements in
the mechanism of labor
and delivery, left
occiput anterior
position
3
0
4
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Mechanism of labor for the left occiput transverse position, lateral view.
Posterior asynclitism (A) at the pelvic brim followed by lateral flexion,
resulting in anterior asynclitism (B) after engagement, further descent
(C), rotation, and extension (D)
OCCIPUT POSTERIOR POSITION
 Mechanism of labour is identical to OT & anterior
varieties
 The occiput rotate to the symphysis pubis through 135º
instead of 90º or 45º
 If rotation does not occur  direct occiput posterior or
partial rotation  transverse arrest
,
.
,
0
Mechanism of labor for right occiput
posterior position, anterior rotation