MECHANISM OF LABOUR MECHANISM OF LABOUR (NORMAL & ABNORMAL)(NORMAL & ABNORMAL)

DR. SALWA NEYAZI

CONSULTANT OBSTETRICIAN GYNECOLOGIST

PEDIATRIC & ADOLESCENT GYNECOLOGIST

Lie, presentation, attitude, &positionLie, presentation, attitude, &position

FETAL LIEFETAL LIE The relation of the long axis of the fetus to that of the motherThe relation of the long axis of the fetus to that of the mother Longitudinal lie is found in 99% of labours at termLongitudinal lie is found in 99% of labours at term Predisposing factors for transverse lie/oblique lie Predisposing factors for transverse lie/oblique lie

multiparity, placenta previa, hydramnious, & uterine multiparity, placenta previa, hydramnious, & uterine anomaliesanomalies

FETAL PRESENTATIONFETAL PRESENTATION The presenting part is the portion of the body of the fetus The presenting part is the portion of the body of the fetus

that is foremost in the birth canalthat is foremost in the birth canal The presenting part can be felt through the Cx on vaginal The presenting part can be felt through the Cx on vaginal

examinationexamination Longitudinal lie Longitudinal lie cephalic presentation cephalic presentation breech presentationbreech presentation Transvrse lie Transvrse lie shoulder presentation shoulder presentation

Lie, presentation, attitude, &positionLie, presentation, attitude, &positionCEPHALIC PRESENTATIONCEPHALIC PRESENTATION Head is flexed sharply Head is flexed sharply vertex / occiput presentation vertex / occiput presentation Head is extended sharply Head is extended sharply face presentation face presentation Partially flexed Partially flexed bregma presenting (sinciput presentation) bregma presenting (sinciput presentation) Partially extended Partially extended brow presentation brow presentation

BREECH PRESENTATIONBREECH PRESENTATION Frank breechFrank breech Complete breechComplete breech Footling breechFootling breech

ATTITUDEATTITUDE Posture of the fetus Posture of the fetus folded on itself to accommodate the shape of folded on itself to accommodate the shape of

the uterusthe uterus Flexed head, thighs, knees &feetFlexed head, thighs, knees &feet The arms crossed over the chestThe arms crossed over the chest Face presentation Face presentation extended concave contour of the vertebral extended concave contour of the vertebral

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A

B

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Longitudinal lie. Ce phalic presentation. Differences in attitude of fetal body,

Note changes in fetal attitude in relation to fetal vertex as the fetal head becomes less flexed.

)A (vertex )B (sinciput )C (brow )D (face

Longitudinal lie. Frank breech presentation.

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Longitudinal lie. Complete breech presentation.

Longitudinal lie. Incomplete, or footling, breech presentation.

POSITIONPOSITION

The relation of an arbitrary chosen point of the fetal The relation of an arbitrary chosen point of the fetal presenting part to the Rt or Lt side of the maternal birth presenting part to the Rt or Lt side of the maternal birth canalcanal

The chosen point The chosen point Vertex presentation Vertex presentation occiput occiput Face presentation Face presentation mentum mentum Breech presentation Breech presentation SacrumSacrum

Each presentation has two positions Rt or LtEach presentation has two positions Rt or Lt

Each position has 3 varieties : Ant, transverse, postEach position has 3 varieties : Ant, transverse, postOA

OP

LOTROT

LOAROA

LOPROP

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LONGITUDINAL LIE VERTEX PRESENTATION

LOA LOP

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Longitudinal lie. Vertex presentation

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

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Right occiput anterior (ROA).

FREQUENCY OF VARIOUS PRESENTATIONS & FREQUENCY OF VARIOUS PRESENTATIONS & POSITIONS AT TERMPOSITIONS AT TERM

Vertex Vertex 96% 96%

2/3 2/3 LtLt

1/3 1/3 RtRt

Breech Breech 3.5% 3.5%

Face Face 0.3%0.3%

Shoulder Shoulder 0.4%0.4%

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

Rt mento-postRt mento-antLt mento-ant

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Longitudinal lie Breech presentation LSP

Transverse lie. Right acromiodorsoposterior position (RADP). The shoulder of the fetus is to the mother's right, and the back is posterior.

MECHANISM OF LABOUR WITH OCCIPUT MECHANISM OF LABOUR WITH OCCIPUT PRESENTATIONSPRESENTATIONS

THE CARDINAL MOVEMENTS OF LABOURTHE CARDINAL MOVEMENTS OF LABOUR

1-ENGAGEMENT1-ENGAGEMENT

The greatest transverse diameter BPD passes through the The greatest transverse diameter BPD passes through the pelvic inletpelvic inlet

It may occur in the last few weeks of pregnancy or only in It may occur in the last few weeks of pregnancy or only in labour especially in multiparalabour especially in multipara

The fetus enters the pelvis in transverse or oblique diameterThe fetus enters the pelvis in transverse or oblique diameter LOT LOT 40% 40% ROT ROT 20%20% OP OP 20% ROP >LOP 20% ROP >LOP ROA / LOAROA / LOA 20%20%

THE CARDINAL MOVEMENTS OF LABOURTHE CARDINAL MOVEMENTS OF LABOUR AsynclitismAsynclitism

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

2-DESCENT2-DESCENT In nullipara engagement takes place before the onset of In nullipara engagement takes place before the onset of

labour & further descent may not occur till the 2labour & further descent may not occur till the 2ndnd stage stage In multipara descent begins with engagement In multipara descent begins with engagement It is gradually progressive till the fetus is deliveredIt is gradually progressive till the fetus is delivered It is affected by the uterine contractions & thinning of the It is affected by the uterine contractions & thinning of the

lower segmentlower segment

Anterior asynclitism Naegele's obliquity

Normal synclitism Posterior asynclitism Litzmann's obliquity Ear presentation

33--FLEXIONFLEXION

The descending head meets resistance of pelvic floor, Cx The descending head meets resistance of pelvic floor, Cx & walls of the pelvis & walls of the pelvis flexion flexion

The shorter suboccipito-begmatic is substituted for the The shorter suboccipito-begmatic is substituted for the longer occipito-frontallonger occipito-frontal

Lever action producing ftexion of the head; conversion from occipitofrontal to suboccipitobregmatic diameter

typically reduces the anteroposterior diameter from nearly 12- to 9.5 cm.

A

c

Four 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 poor.B. Flexion moderate. C. Flexion advanced. D. Flexion complete.

Note that with flexion com plete 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

44--INTERNAL ROTATIONINTERNAL ROTATION

Turning of the head from the OT position Turning of the head from the OT position anteriorly anteriorly towards the symphysis pubis ie. Occiput moves from towards the symphysis pubis ie. Occiput moves from transverse to ant 45ºtransverse to ant 45º

Less commonly OT Less commonly OT posteriorly towards the sacrum posteriorly towards the sacrum 135º135º

It is not accomplished till the head has reached the spinesIt is not accomplished till the head has reached the spinesThe levator ani muscles form a V shaped sling that tend to The levator ani muscles form a V shaped sling that tend to

rotate the vertex anteriorlyrotate the vertex anteriorly

It is completed by the time the head reaches the pelvic It is completed by the time the head reaches the pelvic floor 2/3 or shortly after ¼floor 2/3 or shortly after ¼

EXTENSIONEXTENSION

When the flexed head reaches the vulva it undergoes When the flexed head reaches the vulva it undergoes extension extension the base of the occiput will be in direct contact the base of the occiput will be in direct contact with the inferior margin of the symphysis pubiswith the inferior margin of the symphysis pubis

Crowning Crowning the largest diameter of the fetal head is the largest diameter of the fetal head is encircled by the vulvar ringencircled by the vulvar ring

The head is born by further extension as the occiput, The head is born by further extension as the occiput, bregma, forehead, nose, mouth & chin pass successively bregma, forehead, nose, mouth & chin pass successively over the perineum over the perineum

EXTERNAL ROTATIONEXTERNAL ROTATIONRESTITUTIONRESTITUTION

After delivery of the head it returns to the position it After delivery of the head it returns to the position it occupied at engagement , the natural position relative to occupied at engagement , the natural position relative to the shoulders (oblique position)Restitutionthe shoulders (oblique position)Restitution

Then the fetal body will rotate to bring one shoulder Then the fetal body will rotate to bring one shoulder anterior behind the symphysis pubis ( biacromial diameter anterior behind the symphysis pubis ( biacromial diameter into the APD of the pelvic outlet)into the APD of the pelvic outlet)

Restitution is followed by complete external rotation to Restitution is followed by complete external rotation to transverse position (occiput lies to next to Lt maternal transverse position (occiput lies to next to Lt maternal thigh)thigh)

The ant shoulder slips under the pubis The ant shoulder slips under the pubis By lateral flexion of the fetal body the post shoulder will be By lateral flexion of the fetal body the post shoulder will be

delivered & the rest of the body will follow 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

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 exten sion (D).

304

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OCCIPUT POSTERIOR POSITIONOCCIPUT POSTERIOR POSITION Mechanism of labour is identical to OT & anterior varieties Mechanism of labour is identical to OT & anterior varieties The occiput rotate to the symphysis pubis through 135º The occiput rotate to the symphysis pubis through 135º

instead of 90º or 45ºinstead of 90º or 45º If rotation does not occurIf rotation does not occur direct occiput post or direct occiput post or

Partial rotation Partial rotation transverse arresttransverse arrest

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

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