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Ch. 11. Parturition

부산백병원 산부인과부산백병원 산부인과

R1 R1 손영실손영실

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# Clinical Course of Labor

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INDEX

1. The Myometrium1. The Myometrium

2. The Cervix2. The Cervix

3. Labor Patterns3. Labor Patterns

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• • Labor : thunderous uterine contractions that effectLabor : thunderous uterine contractions that effect

dilatation of the cervix and force the fetusdilatation of the cervix and force the fetus

through the birth canalthrough the birth canal

• • False labor : myometrial contractions that do notFalse labor : myometrial contractions that do not

cause cervical dilatationcause cervical dilatation 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

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The Myometrium1. Anatomical and Physiological 1. Anatomical and Physiological

ConsiderationsConsiderations

• • Characteristics – advantage in the efficiency of Characteristics – advantage in the efficiency of uterineuterine

contractions & the delivery of contractions & the delivery of the fetusthe fetus

① ① degree of shortening of smooth muscle cells degree of shortening of smooth muscle cells withwith

contractioncontraction : magnitude greater than in striated : magnitude greater than in striated

muscle cellsmuscle cells ② ② forces can be exerted in smooth muscle forces can be exerted in smooth muscle

cells incells in any directionany direction ③ ③ not organized in the same manner as not organized in the same manner as

skeletal muscleskeletal muscle - thick & thin filaments in long, random - thick & thin filaments in long, random

bundlesbundles → → greater shortening & force-generating greater shortening & force-generating

capacitycapacity

④ ④ multidirectional force generationmultidirectional force generation

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2. Biochemistry of Smooth Muscle Contractions2. Biochemistry of Smooth Muscle Contractions

The Myometrium

ContractiContractionon Myosin light chain

Myosin light chain kinaseCa2+ activated

PhosphorylatedMyosin light chain

Actin

Actin-Phosphorylated MyowinATPase

ATP ADP

RelaxatiRelaxationon

1) Decreased intracellular Ca2+; Ca2+ sequestration

2) Dephosphorylation of myosin light chain

3) Inactivation of myosin light chain kinase (e.g., by cyclic AMP- dependent phosphorylation)

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3. The Three Stages of Labor3. The Three Stages of Labor

• • First stage of laborFirst stage of labor

: begins when uterine contraction of sufficient: begins when uterine contraction of sufficient

frequency, intensity & duration are attainedfrequency, intensity & duration are attained

→ → ends when cervix is fully dilatated (10cm)ends when cervix is fully dilatated (10cm)

: : stage of cervical effacement & dilatationstage of cervical effacement & dilatation

The Myometrium

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• • Second stage of laborSecond stage of labor

: begins when complete dilatation of cervix: begins when complete dilatation of cervix

→ → ends with delivery of the fetusends with delivery of the fetus

: : stage of expulsion of the fetusstage of expulsion of the fetus

• • Third stage of laborThird stage of labor

: begins after delivery of the fetus: begins after delivery of the fetus

→ → ends with the delivery of the placentaends with the delivery of the placenta

: : stage of separation & expulsion of stage of separation & expulsion of placentaplacenta

The Myometrium

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4. Clinical Onset of Labor4. Clinical Onset of Labor

• • Show (bloody show)Show (bloody show)

- sign of the impending onset of active - sign of the impending onset of active laborlabor

- extrusion of mucus plug of the cervical - extrusion of mucus plug of the cervical canalcanal

→ → discharge of small amount of blood-discharge of small amount of blood-tingedtinged

mucus from vaginamucus from vagina

The Myometrium

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5. Uterine Contractions Characteristic of Labor5. Uterine Contractions Characteristic of Labor

; muscular contractions, those of uterine smooth; muscular contractions, those of uterine smooth

muscle of labor are painfulmuscle of labor are painful

• • cause of pain (not known definitely)cause of pain (not known definitely)

① ① hypoxia of contracted myometriumhypoxia of contracted myometrium

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

uterus by the tightly interlocking muscle bundlesuterus by the tightly interlocking muscle bundles

③ ③ stretching of cervix during dilatationstretching of cervix during dilatation

④ ④ stretching of peritoneum overlying the fundusstretching of peritoneum overlying the fundus

The Myometrium

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• • Ferguson reflexFerguson reflex

: mechanical stretching of cervix enhances : mechanical stretching of cervix enhances uterineuterine

activityactivity : manipulation of the cervix and stripping : manipulation of the cervix and stripping

the fetalthe fetal membranes is associated with an increase membranes is associated with an increase

in PGFin PGF2α2α

metabolite in bloodmetabolite in blood

: exact mechanism : not clear: exact mechanism : not clear

• • Interval between contractionsInterval between contractions

: 10 minutes at the onset of the first stage: 10 minutes at the onset of the first stage → → diminishes graduallydiminishes gradually → → 1 minute or less in the second stage1 minute or less in the second stage

The Myometrium

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• • Periods of relaxation between contractionsPeriods of relaxation between contractions

- essential to welfare of the fetus- essential to welfare of the fetus

- unremitting contraction of uterus compromises- unremitting contraction of uterus compromises

uteroplacental blood flow, cause fetal hypoxiauteroplacental blood flow, cause fetal 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)

Pressure 20-60 mmHg (average 40 mmHg)Pressure 20-60 mmHg (average 40 mmHg)

The Myometrium

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6. Differentiation of Uterine Activity6. Differentiation of Uterine Activity : During active labor, uterus is transformed : During active labor, uterus is transformed

intointo 2 distinct parts2 distinct parts

(1) Upper segment(1) Upper segment ① ① 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 segment(2) Lower segment ① ① relatively passiverelatively passive ② ② develops into a much thinly walled develops into a much thinly walled

passagepassage for the fetusfor the fetus ③ ③ much less firmmuch less firm

The Myometrium

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• • Physiologic retraction ringPhysiologic retraction ring

- As a result of the thinning of the lower uterine- As a result of the thinning of the lower uterine

segment and the concomitant thickening of thesegment and the concomitant thickening of the

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

by a ridge on the inner uterine surfaceby a ridge on the inner uterine surface

• • Pathologic retraction ring (the ring of Bandle)Pathologic retraction ring (the ring of Bandle)

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

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

prominentprominent

The Myometrium

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The Myometrium

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7. Change in Uterine Shape7. Change in Uterine Shape : each contraction produces elongation of : each contraction produces elongation of

uterus withuterus 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

② ② lengthening of uteruslengthening of uterus → → longitudinal fibers are drawn tautlongitudinal fibers are drawn taut → → pulled upward the lower segment & pulled upward the lower segment &

cervixcervix → → important factor in cervical dilatationimportant factor in cervical dilatation

The Myometrium

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8. Ancillary Forces in Labor8. Ancillary Forces in Labor : After the cervix is dilated fully, the most important: After the cervix is dilated fully, the most important force in the expulsion of the fetus is that producedforce in the expulsion of the fetus is that produced by increased maternal intrabdominal pressureby increased maternal intrabdominal pressure

““Pushing”Pushing” - increased intrabdominal pressure by contraction of- increased intrabdominal pressure by contraction of abdominal muscles, simultaneously with forcedabdominal muscles, simultaneously with forced respiratory efforts with glottis closedrespiratory efforts with glottis closed - important force in the expulsion of fetus- important force in the expulsion of fetus - similar to that involved in defecation- similar to that involved in defecation

The Myometrium

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1. Changes Induced in the Cervix with Labor1. Changes Induced in the Cervix with Labor

• • Effective force of the 1st stage of labor is Effective force of the 1st stage of labor is uterineuterine

contractioncontraction

• • As the result of the action of these forces, As the result of the action of these forces, twotwo

fundamental changes take place in the fundamental changes take place in the alreadyalready

ripened cervixripened cervix

““effacement & dilatation”effacement & dilatation”

• • The cervix is said to be completely (fully)The cervix is said to be completely (fully)

dilated : 10 cmdilated : 10 cm

The Cervix

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2. Cervical Effacement2. Cervical Effacement

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

• • shortening of the cervical canal (2cm → mere circularshortening of the cervical canal (2cm → mere circular

orifice with almost paper thin edge)orifice with almost paper thin edge)

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

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

segmentsegment

• • external os remains temporarily unchangedexternal os remains temporarily unchanged

The Cervix

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The Cervix

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The Cervix

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3. Cervical Dilatation3. Cervical Dilatation : as the uterine contraction cause pressure on the: as the uterine contraction cause pressure on the membranes → the hydrostatic action of the amnionicmembranes → the hydrostatic action of the amnionic sac in turn dilates the cervical canalsac in turn dilates the cervical canal

The Cervix

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1. Pattern of Cervical Dilatation1. Pattern of Cervical Dilatation

• • FriedmanFriedman

“ “Except for Except for cervical dilatation & fetal cervical dilatation & fetal descentdescent,,

none of the clinical features of parturient none of the clinical features of parturient appearsappears

to be useful in assessing labor to be useful in assessing labor progression”progression”

• • pattern of cervical dilatation during normal pattern of cervical dilatation during normal laborlabor

course : sigmoid curvecourse : sigmoid curve

Labor Patterns

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- 2 phases of cervical dilatation- 2 phases of cervical dilatation (1) Latent phase(1) Latent phase : more variable: more variable : subject to sensitive changes by extraneous factors: subject to sensitive changes by extraneous factors and by sedation (prolongation) and myometrialand by sedation (prolongation) and myometrial stimulation (shortening)stimulation (shortening)

(2) Active phase(2) Active phase ① ① Acceleration phaseAcceleration phase usually predictive of the outcome of a particular laborusually predictive of the outcome of a particular labor ② ② Phase of maximum slopePhase of maximum slope good measure of the overall efficiency of the machinegood measure of the overall efficiency of the machine ③ ③ Deceleration phaseDeceleration phase more reflective fetopelvic relationshipmore reflective fetopelvic relationship

Labor Patterns

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- 2nd stage of labor commences after complete - 2nd stage of labor commences after complete cervicalcervical

dilatation→ only progressive descent of fetal dilatation→ only progressive descent of fetal presentingpresenting

part is available to assess the progress of part is available to assess the progress of laborlabor

Labor Patterns

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2. Pattern of Descent2. Pattern of Descent - In many nulliparas,- In many nulliparas, ① ① engagement is accomplished before labor beginsengagement is accomplished before labor begins ② ② further descent does not occur until late in laborfurther descent does not occur until late in labor ③ ③ increased rates of descent are ordinarily observedincreased rates of descent are ordinarily observed during the phase of maximum slopeduring the phase of maximum slope

Labor Patterns

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3. Criteria of Normal Labor3. Criteria of Normal Labor • • FriedmanFriedman : Concept of 3 functional divisions of labor: Concept of 3 functional divisions of labor

① ① Preparatory divisionPreparatory division - latent & acceleration phases- latent & acceleration phases - sensitive to sedation & conduction analgesia- sensitive to sedation & conduction analgesia - little cervical dilatation occurs, considerable- little cervical dilatation occurs, considerable changes take place in the extracellular matrix ofchanges take place in the extracellular matrix of cervix (collagen & other connective tissuecervix (collagen & other connective tissue component)component)

Labor Patterns

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② ② Dilatational divisionDilatational division

- phase of maximum slope of cervical - phase of maximum slope of cervical dilatationdilatation

- most rapid rate of dilatation occur- most rapid rate of dilatation occur

- unaffected by sedation or conduction - unaffected by sedation or conduction analgesiaanalgesia

③ ③ Pelvic divisionPelvic division

- deceleration phase & second stage- deceleration phase & second stage

- involve the cardinal movement of the - involve the cardinal movement of the fetusfetus

Labor Patterns

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4. Rupture of the Fetal Membranes4. Rupture of the Fetal Membranes

- spontaneous rupture of membrane most - spontaneous rupture of membrane most often(+)often(+)

sometime during the course of active laborsometime during the course of active labor

- premature rupture of the membrane- premature rupture of the membrane

: rupture of membranes before the onset : rupture of membranes before the onset of laborof labor

at any stage of gestationat any stage of gestation

Labor Patterns

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5. Placental Separation5. Placental Separation

““3rd stage of labor”3rd stage of labor”

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

involve the separation & expulsion of the involve the separation & expulsion of the placentaplacenta

• • after delivery of placenta & fetal after delivery of placenta & fetal membranes,membranes,

active labor is completedactive labor is completed

• • occurs within a very few minutes after occurs within a very few minutes after deliverydelivery

Labor Patterns

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6. Separation of Amniochorion6. Separation of Amniochorion

: great decrease in the surface area of uterine cavity: great decrease in the surface area of uterine cavity → → fetal membranes (amniochorion) & parietalfetal membranes (amniochorion) & parietal decidua to be thrown into innumerable foldsdecidua to be thrown into innumerable folds → → increase thickness of the layer from less thanincrease thickness of the layer from less than 1 mm to 3-4 mm1 mm to 3-4 mm

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

Labor Patterns

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Labor Patterns

7. Placental Extrusion7. Placental Extrusion

: women in recumbent position frequently cannot expel: women in recumbent position frequently cannot expel

placenta spontaneouslyplacenta spontaneously

→ → artificial means of completing the 3rd stage isartificial means of completing the 3rd stage is

generally requiredgenerally required

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

minimal traction on umbilical cordminimal traction on umbilical cord

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Labor Patterns

8. Mechanisms of Placental Extrusion8. Mechanisms of Placental Extrusion

(1) Schultze mechanism(1) Schultze mechanism • • placental separation occurs first at central areasplacental separation occurs first at central areas → → retroplacental hematomaretroplacental hematoma → → push the placenta toward uterine cavitypush the placenta toward uterine cavity

(2) Duncan mechanism(2) Duncan mechanism ① ① placental separation occurs first at the peripheryplacental separation occurs first at the periphery ② ② blood collects between the membranesblood collects between the membranes & uterine wall& uterine wall → → escapes from the vaginaescapes from the vagina

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