1

Ch11. Parturition

부산백병원 산부인과R2 정은정

Williams Obstetrics p151~181

2

Phases of parturition Labor : uterine contractions that effect Labor : uterine contractions that effect

dilatation of cervix and force fetus through dilatation of cervix and force fetus through birth canalbirth 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

3

Fig 6-1 Phases of parturition & onset of labor

Divide four uterine phase : correspond to major physiological transient of myometrium and cervix during pregnancy

4

Phase 0 of parturition : Ut Quiescence

Uterine smooth m tranquility with maintenance of cervical structural intergrity

Unresponsive to natural stimuli, contractile paralysis Myometrium : quiescent state Cx : firm unyielding Succesful anatomical structural integrity :essential for

successful parturition Some myometrial contraction occur not cause Cx dilat

ion Braxton – Hicks contraction or false labor

5

• • Braxton – Hicks contraction or false labor : :

Myometrial contractions that do not cause cervical dilatMyometrial contractions that do not cause cervical dilatationation

unpredictability in occurrenceunpredictability in occurrence lack of intensitylack of intensity

brevity of durationbrevity of duration discomfort – confined to low abdomen & groindiscomfort – confined to low abdomen & groin

Phase 0 of parturition : Ut Quiescence

6

Phase 1 of parturition : preparation for labor

Uterine awakening or activation Progression of change in Ut during last 6~8 w

k of pregnancy.

Cervial change Myometrial change

7

Phase 1 of parturition : Cervial 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

8

Phase 1 of parturition : Cervial change Change of state of bundles of collagen fiber

• Collagen breakdown ↑ & rearrangement of collagen fiber bundles (No & 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

9

PG E2 & F2a : modification of collagen & alteration in relative amount of glycosaminoglycans

Cx softening or ripenning to facilitate induction of labor

Cervical change

10

Increase Ut irritability & responsiveness to uterotonins

Alterations in expression of key enzyme. CAP(contraction-associated proteins)-control myometrum contractility

Myometrial oxytocin R ↑ Myometrial cell gap junction protein (ex connexin -

43)

Formation lower Ut segment

Myometrial change

11

Phase2 of parturition :process of labor

Active labor : Ut contrations bring about progressive cervical dilatation & delivery

3 stage of labor

12

• Three Stages of LaborThree Stages of Labor

• First stage of laborFirst stage of labor•

• begins when uterine contraction of sufficient frequencbegins when uterine contraction of sufficient frequency, intensity & durationy, intensity & duration

• ends when Cx is fully dilatated (10cm)ends when Cx is fully dilatated (10cm)

• Stage of cervical effacement & dilatationStage of cervical effacement & dilatation

Phase2 of parturition :process of labor

13

Phase2 of parturition :process of labor

Second stage of laborSecond stage of labor begins when complete dilatation of Cxbegins when complete dilatation of Cx ends with delivery of fetusends with delivery of fetus stage of expulsion of fetusstage of expulsion of fetus

Third stage of laborThird stage of labor begins after delivery of fetusbegins after delivery of fetus ends with delivery of placenta and fetal membends with delivery of placenta and fetal memb

rnaernae stage of separation & expulsion of placentastage of separation & expulsion of placenta

14

• Show (bloody show)Show (bloody show)

- sign of initiation of labor- sign of initiation of labor

- spontaneous discharge of small amount of - spontaneous discharge of small amount of blood-tinged mucus from vaginablood-tinged mucus from vagina

-labor already in progress or ensue during next -labor already in progress or ensue during next several hours to daysseveral hours to days

1st stage of Labor : 1st stage of Labor : Clinical Onset of LaborClinical Onset of Labor

15

★★Uterine Contractions Characteristic of LaborUterine Contractions Characteristic of Labor• Contraction of Ut smooth m during labor : painfulContraction of Ut smooth m during labor : painful• Involuntary, independent of extraut. controlInvoluntary, independent of extraut. control

• • Cause of painCause of pain (not known definitely) (not known definitely) ① ① hypoxia of contracted myometriumhypoxia of contracted myometrium

② ② compression of nerve ganglia in Cx & lowercompression of nerve ganglia in Cx & lower

uterus by interlocking muscle bundlesuterus by interlocking muscle bundles

③ ③ stretching of Cx during dilatationstretching of Cx during dilatation

④ ④ stretching of peritoneum overlying fundusstretching of peritoneum overlying fundus

1st stage of Labor : 1st stage of Labor : Clinical Onset of LaborClinical Onset of Labor

16

• • Ferguson reflexFerguson reflex : mechanical stretching of Cx enhances uterine: mechanical stretching of Cx enhances uterine activity activity exact mechanism : not clearexact mechanism : not clear

: manipulation of Cx and stripping fetal: manipulation of Cx and stripping fetal membranes is associated with increase inmembranes is associated with increase in PGFPGF2α2αmetabolite (PGFM) in bloodmetabolite (PGFM) in bloodcontractioncontraction • • Interval between contractionsInterval between contractions : 10 minutes at onset of 1st stage: 10 minutes at onset of 1st stage → → diminishes graduallydiminishes gradually 1 minute or less in 2nd stage1 minute or less in 2nd stage

1.1.1st stage of Labor : 1st stage of Labor : Clinical Onset of LaborClinical Onset of Labor

17

• • Periods of relaxation between contractionsPeriods of relaxation between contractions - essential to welfare of fetus- essential to welfare of fetus

- unremitting contraction of uterus - unremitting contraction of uterus

compromises uteroplacental blood flowcompromises uteroplacental blood flow

fetal hypoxiafetal hypoxia

• • Duration of contractionDuration of contraction : in active phase: in active phase

Duration 30-90 seconds (average 60 sec)Duration 30-90 seconds (average 60 sec)

AF Pr 20-60 mmHg (average 40 mmHg)AF Pr 20-60 mmHg (average 40 mmHg)

1.1.1st stage of Labor : 1st stage of Labor : Clinical Onset of LaborClinical Onset of Labor

18

★★ Formation of distinct lower & upper UtFormation of distinct lower & upper Ut segmentsegment : : 2 distinct parts (anatomically & 2 distinct parts (anatomically & physiologically)physiologically) 1) Upper segment1) Upper segment

①① actively contractingactively contracting ② ② becomes thicker as labor advancesbecomes thicker as labor advances ③ ③ quite firm or hardquite firm or hard 2) Lower segment2) Lower segment ① ① relatively passiverelatively passive ② ② develops into a much thinly walled passagedevelops into a much thinly walled passage for the fetusfor the fetus ③ ③ much less firmmuch less firm

1.1.1st stage of Labor : 1st stage of Labor : Clinical Onset of LaborClinical Onset of Labor

19

1)Upper segment1)Upper segment• Contract, retract, expel fetus Myometrium of upper segment not relax to original lengh aft

er contraction fixed at shorter Myometrial tension remains constant Upper part of Ut cavity smaller with each successive contrac

tion Successive shortening of muscular fibers with contractions Upper Active Ut segment : progressively thickend throughosegment : progressively thickend througho

ut 1st & 2ut 1st & 2ndnd stage of labor stage of labor

1st stage of Labor : Clinical 1st stage of Labor : Clinical Onset of LaborOnset of Labor

20

2) Lower segment2) Lower segment

• Fibers become stretched with each contraction Fibers become stretched with each contraction • of upper segment of upper segment • Lower segment not returned to previous Lower segment not returned to previous • length but remain fixed at longer lengthlength but remain fixed at longer length• Tension remain same as beforeTension remain same as before• Successive lengthening of fibers in lower Successive lengthening of fibers in lower segment,as labor progresssegment,as labor progress thinning normally to only a few mm inthinnestthinning normally to only a few mm inthinnest partpart

1st stage of Labor : Clinical 1st stage of Labor : Clinical Onset of LaborOnset of Labor

21

• • Physiologic retraction ringPhysiologic retraction ring

- As result of thinning of lower uterine- As result of thinning of lower uterine

segment and concomitant thickening of thesegment and concomitant thickening of the

upper, boundary between the two is markedupper, boundary between the two is marked

by ridge on inner uterine surfaceby ridge on inner uterine surface

• • Pathologic retraction ring (Bandl ring)Pathologic retraction ring (Bandl ring)

- When thinning of lower uterine segment is- When thinning of lower uterine segment is

extreme, as in obstructed labor, ring is veryextreme, as in obstructed labor, ring is very

prominentprominent

1st stage of Labor : 1st stage of Labor : Clinical Onset of LaborClinical Onset of Labor

22

Sequence of development of segment & ring in ut in preg women at term & in labor

23

★★ Change in Uterine ShapeChange in Uterine Shape : each contraction produces elongation of uterus with: each contraction produces elongation of uterus with decrease in horizontal diameterdecrease in horizontal diameter → → important effect on labor processimportant effect on labor process

① ① decrease in horizontal diameterdecrease in horizontal diameter → → straightening of fetal vertebral columnstraightening of fetal vertebral column

press upper pole of fetus firmly aganst funduspress upper pole of fetus firmly aganst fundus

② ② lengthening of uteruslengthening of uterus → → longitudinal fibers are drawn taut → lower segment &longitudinal fibers are drawn taut → lower segment & cervix are pulled upward over lower pole of fetuscervix are pulled upward over lower pole of fetus → → important factor in cervical dilatationimportant factor in cervical dilatation

1st stage of labor : clinical onset of Labor

24

★★ Ancillary Forces in LaborAncillary Forces in Labor : : After Cx is dilated fully, most importantAfter Cx is dilated fully, most important force in expulsion of fetus force in expulsion of fetus increased maternal increased maternal intrabdominal pressureintrabdominal pressure

““Pushing”Pushing” - increased intrabdominal pressure by- increased intrabdominal pressure by contraction of abdominal m, simultaneously withcontraction of abdominal m, simultaneously with forced respiratory efforts with glottis closedforced respiratory efforts with glottis closed - important force in expulsion of fetus- important force in expulsion of fetus - similar to defecation- similar to defecation

1st stage of labor : clinical onset of Labor

25

1. 1. Changes Induced in the Cervix with LaborChanges Induced in the Cervix with Labor

• • Effective force of 1st stage of labor is uterineEffective force of 1st stage of labor is uterine

contractioncontraction

• • As result of action of these forces, twoAs result of action of these forces, two

fundamental changes take place in the alreadyfundamental changes take place in the already

ripened cervixripened cervix

““effacement & dilatation”effacement & dilatation” • • Cx completely (fully) dilated : 10 cmCx completely (fully) dilated : 10 cm

Cervical change induced during 1st stage of lobor

26

2. Cervical Effacement2. Cervical Effacement

• • obliteration or taking up of cervixobliteration or taking up of cervix

• • shortening of the cervical canal (2cm → shortening of the cervical canal (2cm →

mere circular orifice with almost paper thin edge)mere circular orifice with almost paper thin edge)

• • muscular fibers at about level of internal osmuscular fibers at about level of internal os

are pulled upward or “taken up” lower uterineare pulled upward or “taken up” lower uterine

segmentsegment

• • external os remains temporarily unchangedexternal os remains temporarily unchanged

Cervical change induced during 1st stage of lobor

27

Figure6-5Cx near end of preg before labor

Figure6-6Beginning effacement of Cx

28

Figure6-6 Cervical canal obliterated

Figure6-6Further effacement of Cx

29

3.3.Cervical DilatationCervical Dilatation

• During contraction centrifugal pull is exerted on During contraction centrifugal pull is exerted on Cx leading to distention, process of Cx DilatationCx leading to distention, process of Cx Dilatation• As uterine contraction cause pressure on theAs uterine contraction cause pressure on the membranes →hydrostatic action of amnionicmembranes →hydrostatic action of amnionic sac (pressure of presenting part) in turn dilates sac (pressure of presenting part) in turn dilates the cervical canalthe cervical canal

Cervical change induced during 1st stage of lobor

30

그림

Cervical change induced during 1st stage of lobor

31

2 2 phases of cervical dilatationphases of cervical dilatation 11) Latent phase) Latent phase : more variable: more variable : subject to sensitive changes by extraneous : subject to sensitive changes by extraneous factors & by sedation (prolongation) &factors & by sedation (prolongation) & myometrial stimulation (shortening)myometrial stimulation (shortening)

2) Active phase2) Active phase ① ① Acceleration phaseAcceleration phase usually predictive of outcome usually predictive of outcome ② ② Phase of maximum slopePhase of maximum slope ③ ③ Deceleration phaseDeceleration phase

Cervical change induced during 1st stage of lobor

32

- In many nulliparasIn many nulliparas

① ① engagement accomplished before labor engagement accomplished before labor begins begins ② ② further descent not occur until late in further descent not occur until late in laborlabor

③ ③ increased rates of descent are ordinarily increased rates of descent are ordinarily observed during the phase of maximum slopeobserved during the phase of maximum slope

2nd stage of labor : fetal descentnd stage of labor : fetal descent

33

2nd stage of labor : fetal descentnd stage of labor : fetal descent

34

Fig 6-12 : Labor course divided fuctionally on basis of expected evolution of dilatati: Labor course divided fuctionally on basis of expected evolution of dilatati

on & desecnt curves into 3 divisions on & desecnt curves into 3 divisions

① ① Preparatory divisionPreparatory division - latent & acceleration phases - latent & acceleration phases

② ② Dilatational divisionDilatational division - phase of maximum slope of cervical dilatation- phase of maximum slope of cervical dilatation - most rapid rate of dilatation occur- most rapid rate of dilatation occur ③ ③ Pelvic divisionPelvic division - deceleration phase & second stage while concurrent with phase of - deceleration phase & second stage while concurrent with phase of

maximum slope of fetal descent maximum slope of fetal descent

2nd stage of labor : fetal descentnd stage of labor : fetal descent

35

Change in pelvic floor during labor

Most important structure : levator ani m & fascia During pregnancy: hypertrophy, forming thick band that extend ba

ckward from pubis & encircles vagina about 2cm above plane of hymen

On contraction, levator ani draw both Rectum & vagina forward & upward in direction of symphysis pubis acts to close vagina

Stretching of fibers of levator ani m & thinning of central portion of perineum transformed from 5cm in thickness to thin trasparent mebranous structure less than 1cm thick

anus markedly dilated, present opening 2~3 cm diameter and through which ant wall of rectum bulges

36

★★ Placental SeparationPlacental Separation

• • begins immediately after delivery of fetus,begins immediately after delivery of fetus,

involve separation & expulsion of placentainvolve separation & expulsion of placenta

••Diminution in Ut sizeDiminution in Ut size PL implantation site areaPL implantation site area ↓ ↓ PL acPL accommodate to reduced area commodate to reduced area thickness because of limi thickness because of limited PL elasiticity ted PL elasiticity forced to buckle forced to buckle

- Resulting tension Resulting tension weakest layer of decidua (D. spongio weakest layer of decidua (D. spongiosa) cleavage take place at that sitesa) cleavage take place at that site

- As separation proceed As separation proceed hematoma forms between sep hematoma forms between separtating PL & remaining Decidua artating PL & remaining Decidua result of separation result of separation

3rd stage of labor : deliver y of 3rd stage of labor : deliver y of PL & membrianePL & membriane

37

Fig 6-13 Diminution in size of Placental site after birth of infant

38

::great decrease in surface area of uterine cavitygreat decrease in surface area of uterine cavity → → fetal membranes (amniochorion) & parietalfetal membranes (amniochorion) & parietal decidua to thrown into innumerable foldsdecidua to thrown into innumerable folds → → increase thickness of layer 1mm increase thickness of layer 1mm 3~4 mm3~4 mm

: membranes usually remain in situ until placental: membranes usually remain in situ until placental separation is nearly completedseparation is nearly completed

33rdrd stage of Labor : Delivery stage of Labor : Delivery of Placenta & membraneof Placenta & membrane

★★ Separation of AmniochorionSeparation of Amniochorion

39

- some casesome case abdominal pr↑ PL be expelled abdominal pr↑ PL be expelled - women in recumbent position frequently women in recumbent position frequently

cannot expel placenta spontaneouslycannot expel placenta spontaneously

→ → artificial means generally requiredartificial means generally required

→ → compress & elevate fundus while exerting compress & elevate fundus while exerting

minimal traction on umbilical cordminimal traction on umbilical cord

3rd stage of Labor : Delivery of 3rd stage of Labor : Delivery of Placenta & membranePlacenta & membrane

★★ Placental ExtrusionPlacental Extrusion

40

★★ Mechanisms of Placental ExtrusionMechanisms of Placental Extrusion (1) Schultze mechanism(1) Schultze mechanism • • PL separation occurs 1st at central areasPL separation occurs 1st at central areas → → retroplacental hematomaretroplacental hematoma → → push placenta toward uterine cavitypush placenta toward uterine cavity (2) Duncan mechanism(2) Duncan mechanism ① ① placental separation occurs first at peripheryplacental separation occurs first at periphery ② ② blood collects between membranes &blood collects between membranes & uterine wall → escapes from vaginauterine wall → escapes from vagina Maternal surface first to appear at vulvaMaternal surface first to appear at vulva

3rd stage of Labor : Delivery of 3rd stage of Labor : Delivery of Placenta & membranePlacenta & membrane

41

Ph3 of parturition : process of labor

Immediately after delivry & for 1hr 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 ( lactatio

n anovulation & amenorrhea)