Lecture 5Lecture 5PHASES OF PARTURITIONPHASES OF PARTURITION

STAGES OF LABORSTAGES OF LABOR

MECHANISM OF NORMAL LABOR IN MECHANISM OF NORMAL LABOR IN OCCIPUT PRESENTATIONOCCIPUT PRESENTATION

Prof. Vlad TICA, MD, PhDProf. Vlad TICA, MD, PhD

PHASES OF PARTURITIONLabor : 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 QUIESCENCEUterine 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

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 0: UT QUIESCENCE

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

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 1: PREPARATION FOR LABOR

PHASE 2 : PROCESS OF LABORActive labor : Ut contrations bring about

progressive cervical dilatation & delivery3 stage of labor

1st STAGE OF LABORbegins when uterine contraction of sufficient

frequency, intensity & durationends when Cx is fully dilatated (10cm)stage of cervical effacement & dilatation

2nd STAGE OF LABORbegins when complete dilatation of Cxends with delivery of fetusstage 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

PHASE 2: PROCESS 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

1st STAGE OF LABOR: CLINICAL ONSET OF LABOR

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

Cervical canal obliteratedFurther effacement of Cx

CERVICAL CHANGE INDUCED DURING 1st 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

CERVICAL CHANGE INDUCED DURING 1st STAGE OF LABOR

• 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

2nd 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

2nd STAGE OF LABOR: FETAL DESCENT

3rd STAGE OF LABOR: DELIVERY OF PLACENTA & MEMBRANES

4th 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)

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

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

.'" '

I! 1\

11

A

B

ii

F

cD

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

((AA ) )vertexvertex ((BB ) )sinciputsinciput ((CC ) )browbrow ((DD ) )faceface

Longitudinal lie. Frank breech presentation.

I I

Longitudinal lie. Complete breech presentation.

Longitudinal lie. Incomplete, or footling, breech presentation

POSITIONThe 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 occiputFace presentation mentumBreech presentation sacrum

Each presentation has 2 positions: Rt or Lt

Each position has 3 varieties : anterior, transverse, posteriorOA

OP

LOTROT

LOAROA

LOPROP

~

'tJ

LONGITUDINAL LIE VERTEX PRESENTATIONLOALOA LOPLOP

s

A

Longitudinal lie. Vertex presentation

Right occiput posterior (ROP)Right occiput posterior (ROP) Right occiput transverse (ROT)Right occiput transverse (ROT)

(1 bJ 3~Sf a!w Ccht p(fit tb fe

w

c

al ta tb oj

Right occiput anterior (ROA)

FREQUENCY OF VARIOUS PRESENTATIONS & POSITIONS

AT TERMVertex 96% 2/3 Lt 1/3 Rt

Breech 3.5%

Face 0.3%

Shoulder 0.4%

Longitudinal lie. Face presentation. Left and right anterior and posterior positions.

Right mento-posteriorRight mento-posteriorRight mento-anteriorRight mento-anteriorLeft mento-anteriorLeft mento-anterior

~

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 LABOUR1 - 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 LABOURAsynclitism

The sagittal sutures of the head deflects ant towards the symphysis pubis or post towards the sacrum

2 - DESCENTIn 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

A

c

4 degrees of head flexion

Indicated by the solid line the occipitomental diameter; the broken line connects the center of the anterior fontanel with posterior fontanel:

A. Flexion poorB. Flexion moderateC. Flexion advancedD. Flexion complete

Note that with flexion complete the chin is on the chest, and the suboccipitobregmatic diameter, the shortest anteroposterior diameter of the fetal head, is passing through the pelvic inlet

A

c

D

4-INTERNAL ROTATIONTurning 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

EXTENSIONWhen 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 RESTITUTIONAfter 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

302

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

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)

304

F

tl

v

ba f s

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 orpartial rotation transverse arrest

Mechanism of labor for right occiput posterior position, anterior rotation

,.

,0