MECHANISM OF LABOURMECHANISM OF LABOUR

Lateefa Al Dakhyel FRCSC, FACOGLateefa Al Dakhyel FRCSC, FACOGAssistant professor & consultantAssistant professor & consultantObstetric & gynecology departmentObstetric & gynecology departmentCollage of medicineCollage of medicineKing Saud UniversityKing Saud University

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 mother1-1-LongitudinalLongitudinal lie -99% of labors at termlie -99% of labors at term2-2-transversetransverse lie lie multiparty, placenta previa, hydramnious, & multiparty, placenta previa, hydramnious, &

uterine anomaliesuterine anomalies3-3-obliqueoblique lie -maternal & fetal axes cross @ 45 angle lie -maternal & fetal axes cross @ 45 angle -most unstable & become longitudinal Or -most unstable & become longitudinal Or

transverse at labor.transverse at labor.

ATTITUDE or postureATTITUDE or posture..In later months 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)Change from this flexed attitude can cause abnormal presentations

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A

B

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

Fetal positionFetal position

The relation of a chosen point of the fetal presenting part to The relation of a chosen point of the fetal presenting part to the Rt or Lt side of the maternal birth canalthe Rt or Lt side of the maternal birth canal

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, post

OA

OP

LOTROT

LOAROA

LOPROP

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 breech (incomplete breech)Footling breech (incomplete breech)

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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%

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

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

3-flexion3-flexion

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.

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 spines

The 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

55--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 (ant.fontanelle), forehead, nose, mouth & chin bregma (ant.fontanelle), forehead, nose, mouth & chin pass successively over the perineum pass successively over the perineum

66--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

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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.

OCCIPUT POSTERIOR POSITIONOCCIPUT POSTERIOR POSITION

Mechanism of labour is identical to OT & anterior varieties Mechanism of labour is identical to OT & anterior varieties Usually more longer.Usually more longer. 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 (5-10%)or direct occiput post (5-10%)or

Partial rotation Partial rotation transverse arresttransverse arrest

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

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Q.1-Commonest presentation during labor is 1-left occiput anterior position (LOA) 2-right occiput anterior (ROA) 3-occiput transverse (OT) 4-left occiput posterior (LOP) Q.2- about breach presentation which is correct 1-beech presentation is the more common in primeparous 2-incomlete breach can’t be delivered vaginally 3-breach presentation can’t be diagnosed clinically 4-all breach presentation should be delivered by C/S Q.3-during labor1-engagment occur when BPD reach the pelvic outlet 2-engagment always occur before onset of labor in prime. 3-if internal rotation to SP is 135 degree it will be OP 4-if the head is flexed it will be face presentation

Thank you