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  outcome unfavorable preg

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  diatation Cx initiate

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

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PHASE 2 : PROCESS OF LABOR

Active labor : Ut contrations bring about progressive cervical dilatation & delivery  3 stage of labor

PHASE 2: PROCESS OF LABOR

1 st STAGE OF LABOR  begins when uterine contraction of sufficient frequency, intensity & duration  ends when Cx is fully dilatated (10cm)  stage of cervical effacement & dilatation 2 nd STAGE OF LABOR  begins when complete dilatation of Cx  ends with delivery of fetus  stage of expulsion of fetus

PHASE 2: PROCESS OF LABOR

3 rd STAGE OF LABOR  begins after delivery of fetus  ends with delivery of placenta and fetal membranes  stage of separation & expulsion of placenta 4 th 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

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1

st

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 1 st STAGE OF LABOR

CERVICAL CHANGE INDUCED DURING 1

st

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

2

nd

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

2

nd

STAGE OF LABOR: FETAL DESCENT

2

nd

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

3

rd

STAGE OF LABOR:

DELIVERY OF PLACENTA & MEMBRANES

4

th

STAGE OF LABOR: IMMEDIATE PUERPERIUM

PHASE 3 OF PARTURITION:

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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  presentation) bregma presenting (sinciput  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  shape of the uterus folded on itself to accommodate the  Flexed head, thighs, knees &feet  The arms crossed over the chest  Face presentation  extended concave contour of the vertebral column

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' I ! 1 \ i i B 1 1 A F 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  Face presentation  occiput mentum  Breech presentation  sacrum Each presentation has 2 positions: Rt or Lt Each position has 3 varieties : anterior, transverse, posterior OA ROA LOA ROT ROP OP LOP LOT

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' t J

LONGITUDINAL LIE VERTEX PRESENTATION

LOA LOP

s A

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

Longitudinal lie. Vertex presentation

w

c a l t a t ~ h t p ( f i t t b f e

w

C c !

S f a Right occiput anterior (ROA)

FREQUENCY OF VARIOUS PRESENTATIONS & POSITIONS AT TERM

 Vertex  2/3 96%  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

 Asynclitism

LABOUR

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 2 nd 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

c A 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 A c D suboccipitobregmatic diameter, the shortest anteroposterior diameter of the fetal head, is passing through the pelvic inlet

4-INTERNAL ROTATION

 Turning of the head from the OT position towards the symphysis pubis ie. Occiput moves from transverse to anterior 45º  anteriorly  Less commonly OT  135º posteriorly towards the sacrum  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 3. Further descent, internal rotation 6. Restitution (external rotation)

Cardinal movements in the mechanism of labor and delivery, left occiput anterior position

4. Complete rotation, beginning extension

a f s

3 0 4

F t l v b 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

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, , 0 Mechanism of labor for right occiput posterior position, anterior rotation