Mechanism of Labour (Normal & Abnormal)

Mechanism of Labour (Normal & Abnormal)

MECHANISM OF LABOUR (NORMAL & ABNORMAL) Lie, presentation, attitude, &position FETAL LIE The relation of the long axis of the fetus to that of the mother Longitudinal lie is found in 99% of labours at term Predisposing factors for transverse lie/oblique lie multiparity, placenta previa, hydramnious, & uterine anomalies 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 Cx on vaginal examination Longitudinal lie cephalic presentation breech presentation Transvrse lie shoulder presentation Lie, presentation, attitude, &position CEPHALIC PRESENTATION Head is flexed sharply vertex / occiput presentation Head is extended sharply face presentation Partially flexed bregma presenting (sinciput presentation) Partially extended brow presentation BREECH PRESENTATION

Frank breech Complete breech Footling breech ATTITUDE 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 Face presentation extended concave contour of the vertebral column . '

" ' I ! 1\ 1 1 A B ii

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

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 occiput Face presentation mentum Breech presentation Sacrum Each presentation has two positions Rt or Lt

Each position has 3 varieties : Ant, transverse, post OA ROA LOA ROT LOT ROP OP


A. Right occiput posterior (ROP) Right occiput transverse (ROT) s A Longitudinal lie. Vertex presentation ~ S f

a ! w C c h t p ( f i t t

b f e w c a l t a Right occiput anterior (ROA).

FREQUENCY OF VARIOUS PRESENTATIONS & POSITIONS AT TERM Vertex 96% 2/3 Lt 1/3 Rt Breech 3.5% Face 0.3% Shoulder 0.4% Lt mento-ant Rt mento-ant

Rt mento-post Longitudinal lie. Face presentation. Left and right anterior and ri posterior positions. ~ 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 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 LABOUR Asynclitism 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 2nd 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 FLEXION-3 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 ftexion of the head; conversion from occipitofrontal to suboccipitobregmatic diameter typically reduces the anteroposterior diameter from nearly 12- to 9.5 cm. A c A

c D 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. INTERNAL ROTATION-4

Turning of the head from the OT position anteriorly towards the symphysis pubis ie. Occiput moves from transverse to ant 45 Less commonly OT posteriorly towards the sacrum 135 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 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)Restitution

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 Lt maternal thigh) The ant 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 Cardinal movements in the mechanism of labor and delivery, left occiput

anterior position. 3 0 2 2.Engagement;descent, flexion 3. Further descent, internal rotation 4. Complete rotation, beginning extension 6. Restitution (external rotation)

3 0 4 F t l v b a f

s 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 135 instead of 90 or 45 If rotation does not occur direct occiput post or

Partial rotation transverse arrest , . , 0 Mechanism of labor for right occiput posterior position, anterior rotation.

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